Improving fan system performance 1989-doe-92pp

T OF EN
ERGY
DEPA
RTMEN
U
E
NITED
STAT S OFA
ERICA
M
Improving
Fan System
Performance
a sourcebook for industry
U.S. Department of Energy
Energy Efficiency and Renewable Energy
One of a
series of
industrial
energy
efficiency
sourcebooks
a sourcebook for industry
Bringing you a prosperous future where energy is clean,
abundant, reliable, and affordable
Improving
Fan System
Performance

Acknowledgments
Improving Fan System Performance: A Sourcebook for Industry has been developed by the U.S. Department
of Energy’s (DOE) Industrial Technologies Program and the Air Movement and Control Association
International, Inc. (AMCA), a DOE Allied Partner. Industrial Technologies and AMCA International
undertook this project as part of a series of sourcebook publications on motor-driven equipment under the
BestPractices effort. Other topics in this series include compressed air systems, pumping systems, and motors
and drives. For more information about the Industrial Technologies’ BestPractices effort and AMCA
International, see Section 3.
AMCA International is a not-for-profit association of the world’s manufacturers of related air system
equipment—primarily, but not limited to fans, louvers, dampers, air curtains, airflow measurement stations,
acoustic attenuators, and other air system components—for industrial, commercial, and residential markets.
The association’s mission is to promote the health and growth of industries covered by its scope and the
members of the association consistent with the interests of the public.
DOE, AMCA International, Lawrence Berkeley National Laboratory, and Resource Dynamics Corporation thank
the staff at the many organizations that so generously assisted in the collection of data for this sourcebook.
The contributions of the following participants are appreciated for their review and input to this sourcebook:
Gary Benson, The New York Blower Company
Frank Breining, Airmaster Fan Company
Don Casada, Diagnostic Solutions, LLC
Brad Gustafson, U.S. Department of Energy
Tom Gustafson, Hartzell Fan, Inc.
Tony Quinn, American Fan Company & Woods USA Division
Paul Saxon, Air Movement and Control Association International, Inc.
Bill Smiley, The Trane Company
Sastry Varanasi, ABB Fan Group North America
Dick Williamson, Twin City Fan Companies, Ltd.
Ron Wroblewski, Productive Energy Solutions
Prepared for: The United States Department of Energy
Air Movement and Control Association International, Inc.
Prepared by: Lawrence Berkeley National Laboratory
Washington, DC
Resource Dynamics Corporation
Vienna, VA
Cover photo credit: Copyright© CML Northern Blower Inc., 1989. All rights reserved. This image may not be reproduced,
stored, or transmitted in any form or means without the prior written consent of the copyright holder.

Quick Start Guide
Section 1: Introduction to Fan Systems
Fans 3
Fan Performance Curves 6
Fan System Components 9
Section 2: Performance Improvement Opportunity Roadmap
1—Assessing Fan System Needs 17
2—Fan Types 19
3—Basic Maintenance 25
4—Common Fan Systems Problems 29
5—Indications of Oversized Fans 33
6—System Leaks 37
7—Configurations to Improve Fan System Efficiency 39
8—Controlling Fans with Variable Loads 43
9—Fan Drive Options 47
10–Multiple-Fan Arrangements 51
11–Fan System Economics 55
Section 3: Programs, Contacts, and Resources
Industrial Technologies Program and BestPractices 59
Air Movement and Control Association International, Inc. (AMCA International) 63
Directory of Contacts 65
Resources and Tools 67
Appendices
Appendix A: Fan System Terminology 75
Appendix B: The Fan System Marketplace 83
iA Sourcebook for Industry
Contents
1
3
15
59
75

Improving Fan System Performanceii

1A Sourcebook for Industry
This sourcebook is designed to provide fan system
users with a reference outlining opportunities to
improve system performance. It is not intended to
be a comprehensive technical text on improving
fan systems, but rather a document that makes users
aware of potential performance improvements,
provides some practical guidelines, and details where
the user can find more help. The sourcebook is
divided into three main sections and appendices.
◆ Section 1: Introduction to Fan Systems
For users unfamiliar with the basics of fans and fan
systems, a brief discussion of the terms, relationships,
and important system design considerations is
provided. This section describes the key factors
involved in fan selection and system design and
provides an overview of different types of fans and
the applications for which they are generally used.
Users already familiar with fan system operation
may want to skip this section. The key terms and
parameters used in selecting fans, designing
systems, and controlling fluid flow are discussed.
◆ Section 2: Performance Improvement
Opportunity Roadmap
This section describes the key components of a fan
system and the opportunities for performance improve-
ments. Also provided is a figurative system diagram
identifying fan system components and performance
improvement opportunities. A set of fact sheets
describing these opportunities in greater detail
follows the diagram. These fact sheets cover:
1. Assessing Fan System Needs
2. Fan Types
3. Basic Maintenance
4. Common Fan Systems Problems
5. Indications of Oversized Fans
6. System Leaks
7. Configurations to Improve Fan System Efficiency
8. Controlling Fans with Variable Loads
9. Fan Drive Options
10. Multiple-Fan Arrangements
11. Fan System Economics
◆ Section 3: Programs, Resources, and Contacts
Section 3 provides a directory of associations and
other organizations involved in the fan marketplace,
along with a listing of the resources, tools, software,
videos, and workshops.
◆ Appendices
The sourcebook includes two appendices. Appendix A
is a glossary that defines terms used in the fan
system industry. Appendix B presents an overview
of the fan system marketplace.
The Systems Approach
The cost-effective operation and maintenance of a
fan system requires attention not only to the needs
of the individual pieces of equipment, but also to
the system as a whole. A “systems approach”
analyzes both the supply and demand sides of the
system and how they interact, essentially shifting
the focus from individual components to total
system performance. Often, operators are so focused
on the immediate demands of the equipment that
they overlook the broader question of how system
parameters are affecting the equipment. The
systems approach usually involves the following
types of interrelated actions:
■ Establishing current conditions and operating
parameters
■ Determining present and estimating future
process production needs
■ Gathering and analyzing operating data and
developing load duty cycles
■ Assessing alternative system designs and
improvements
■ Determining the most technically and
economically sound options, taking into
consideration all of the subsystems
■ Implementing the best option
■ Assessing energy consumption with respect to
performance
■ Continuing to monitor and optimize the system
■ Continuing to operate and maintain the system
for peak performance.
Quick Start Guide
Quick Start Guide

2 Improving Fan System Performance

A Sourcebook for Industry 3
Fans1 are widely used in industrial and commercial
applications. From shop ventilation to material
handling to boiler applications, fans are critical
for process support and human health. In the
manufacturing sector, fans use about 78.7 billion
kilowatt-hours2 of energy each year. This con-
sumption represents 15 percent of the electricity
used by motors.3 Similarly, in the commercial
sector, electricity needed to operate fan motors
composes a large portion of the energy costs for
space conditioning.
Performance may range from “free air” to several
pounds per square inch gage (psig)4, with
airflow from a few cubic feet per minute (cfm)
to more than 1 million cfm. Pressures above
15 psig generally require air compressors, which
are addressed in a separate sourcebook titled
Improving Compressed Air System Performance,
A Sourcebook for Industry.
In manufacturing, fan reliability is critical to plant
operation. For example, where fans serve material
handling applications, fan failure will immediately
create a process stoppage. In industrial ventilation
applications, fan failure will often force a process
to be shut down (although there is often enough
time to bring the process to an orderly stoppage).
Even in heating and cooling applications, fan
operation is essential to maintain a productive work
environment. Fan failure leads to conditions in
which worker productivity and product quality
declines. This is especially true for some production
applications in which air cleanliness is critical to
minimizing production defects (for example,
plastics injection molding and electronic component
manufacturing).
In each case, fan operation has a significant impact
on plant production. The importance of fan reliability
often causes system designers to design fan
systems conservatively. Concerned about being
responsible for under-performing systems, designers
tend to compensate for uncertainties in the design
process by adding capacity to fans. Unfortunately,
oversizing fan systems creates problems that can
increase system operating costs while decreasing
fan reliability.
Fans that are oversized for their service requirements
do not operate at their best efficiency points. In
severe cases, these fans may operate in an unstable
manner because of the point of operation on the
fan airflow-pressure curve. Oversized fans generate
excess flow energy, resulting in high airflow noise
and increased stress on the fan and the system.
Consequently, oversized fans not only cost more to
purchase and to operate, they create avoidable
system performance problems. The use of a
“systems approach” in the fan selection process
will typically yield a quieter, more efficient, and
more reliable system.
Fans
There are two primary types of fans: centrifugal
and axial. These types are characterized by the
path of the airflow through the fan. Centrifugal
fans use a rotating impeller to increase the velocity
of an airstream. As the air moves from the impeller
hub to the blade tips, it gains kinetic energy. This
kinetic energy is then converted to a static pressure
increase as the air slows before entering the discharge.
Centrifugal fans are capable of generating relatively
high pressures. They are frequently used in “dirty”
airstreams (high moisture and particulate content),
in material handling applications, and in systems
at higher temperatures.
Section 1: Introduction to Fan Systems
1 For the purposes of this sourcebook, the term “fan” will be used for all air-moving machines other than compressors.
2 United States Industrial Electric Motor Systems Market Opportunities Assessment, U. S. Department of Energy, December 1998.
3 Ibid.
4 At standard conditions, a column of water 27.68 inches high exerts 1 psig of pressure. Equivalently, 1 inch of water gage =
0.036 psig.
Introduction to Fan Systems

Improving Fan System Performance4
Axial fans, as the name implies, move an airstream
along the axis of the fan. The air is pressurized by
the aerodynamic lift generated by the fan blades,
much like a propeller and an airplane wing.
Although they can sometimes be used interchange-
ably with centrifugal fans, axial fans are commonly
used in “clean air,” low-pressure, high-volume
applications. Axial fans have less rotating mass and
are more compact than centrifugal fans of compa-
rable capacity. Additionally, axial fans tend to have
higher rotational speeds and are somewhat noisier
than in-line centrifugal fans of the same capacity;
however, this noise tends to be dominated by high
frequencies, which tend to be easier to attenuate.
◆ Fan Selection
Fan selection is a complex process that starts with
a basic knowledge of system operating requirements
and conditions such as airflow rates, temperatures,
pressures, airstream properties, and system layout.
The variability of these factors and other consider-
ations, such as cost, efficiency, operating life,
maintenance, speed, material type, space con-
straints, drive arrangements, temperature, and
range of operating conditions, complicate fan
selection. However, knowledge of the important
factors in the fan selection process can be helpful
for the purposes of reducing energy consumption
during system retrofits or expansions. Often, a fan
type is chosen for nontechnical reasons, such as
price, delivery, availability, or designer or operator
familiarity with a fan model. If noise levels, energy
costs, maintenance requirements, system reliability,
or fan performance are worse than expected, then
the issue of whether the appropriate fan type was
initially selected should be revisited.
Fans are usually selected from a range of models
and sizes, rather than designed specifically for
a particular application. Fan selection is based
on calculating the airflow and pressure require-
ments of a system, then finding a fan of the right
design and materials to meet these requirements.
Unfortunately, there is a high level of uncertainty
associated with predicting system airflow and
pressure requirements. This uncertainty, combined
with fouling effects and anticipated capacity
expansion, encourages the tendency to increase
the specified size of a fan/motor assembly.
Designers tend to protect against being responsible
for inadequate system performance by “over-
specifying.” However, an oversized fan/motor
assembly creates a different set of operating
problems, including inefficient fan operation,
excess airflow noise, poor reliability, and pipe/duct
vibrations. By describing some of the problems
and costs associated with poor fan selection, this
sourcebook is intended to help designers and oper-
ators improve fan system performance through bet-
ter fan selection and improved operating and
maintenance practices.
Noise. In industrial ventilation applications, noise
can be a significant concern. High acoustic levels
promote worker fatigue. The noise generated by a
fan depends on fan type, airflow rate, and pressure.
Inefficient fan operation is often indicated by a
comparatively high noise level for a particular fan
type.
If high fan noise levels are unavoidable, then
ways to attenuate the acoustic energy should be
considered. Noise reduction can be accomplished
by several methods: insulating the duct; mounting
the fan on a soft material, such as rubber or suit-
able spring isolator as required to limit the amount
of transmitted vibration energy; or installing sound
damping material or baffles to absorb noise energy.
Rotational Speed. Fan rotational speed is typically
measured in revolutions per minute (rpm). Fan
rotational speed has a significant impact on fan
performance, as shown by the following fan laws:
RPMfinal
Airflowfinal = Airflowinitial ( )RPMinitial
RPMfinal
Pressurefinal = Pressureinitial ( )
2
RPMinitial
RPMfinal
Powerfinal = Powerinitial ( )
3
RPMinitial

Rotational speed must be considered concurrently
with other issues, such as variation in the fan load,
airstream temperature, ambient noise, and
mechanical strength of the fan.
Variations and uncertainties in system requirements
are critical to fan type and fan rotational speed
selection. Fans that generate high airflow at
relatively low speeds (for example, forward-curved
blade centrifugal fans) require a relatively accurate
estimate of the system airflow and pressure demand.
If, for some reason, system requirements are
uncertain, then an improper guess at fan rotational
speed can cause under-performance or excessive
airflow and pressure.
Airstream temperature has an important impact on
fan-speed limits because of the effect of heat on
the mechanical strength of most materials. At high
temperatures, all materials exhibit lower yield
strengths. Because the forces on shafts, blades, and
bearings are proportional to the square of the
rotational speed, high-temperature applications are
often served by fans that operate at relatively low
speeds.
Airstream Characteristics. Moisture and particulate
content are important considerations in selecting
fan type. Contaminant build-up on fan blades can
cause severe performance degradation and fan
imbalance. Build-up problems are promoted by a
shallow blade angle with surfaces that allow con-
taminants to collect. Fans with blade shapes that
promote low-velocity air across the blades, such as
backward inclined fans, are susceptible to
contaminant build-up. In contrast, radial tip fans
and radial blade fans operate so that airflow across
the blade surfaces minimizes contaminant build-up.
These fans are used in “dirty” airstreams and in
material handling applications.
Corrosive airstreams present a different set of
problems. The fan material, as well as the fan type,
must be selected to withstand corrosive attack.
Also, leakage into ambient spaces may be a
concern, requiring the fan to be equipped with a
shaft seal. Shaft seals prevent or limit leakage from
around the region where the drive shaft penetrates
the fan housing. For example, in corrosive environ-
ments fans can be constructed with expensive alloys
that are strong and corrosion resistant, or they can
be less expensively constructed with fiberglass-
reinforced plastic or coated with a corrosion-
resistant material. Because coatings are often less
expensive than superalloy metals, fan types that
work well with coatings (for example, radial fan
blades because of their simple shape) are widely
used in corrosive applications; however, wear will
reduce the reliability of coatings. Alternately, mate-
rials such as reinforced fiberglass plastics have
been developed for fan applications and function
effectively in many corrosive environments.
However, there may be size and speed limitations
for composite materials and plastic materials.
Airstreams with high particulate content levels can
also be problematic for the fan drive train. In direct
drive axial fans, the motor is exposed to the
airstream. Sealed motors can be used in these
applications but tend to be more expensive and,
in the event of lost seal integrity, they are suscepti-
ble to expensive damage. In axial fans, belt drives
offer an advantage by removing the motor from the
airstream. In centrifugal fans, the particulate
content is less of a factor because the motor or
sheave can be located outside of the fan enclosure
and connected to the impeller through a shaft seal.
Gear drives are occasionally used in applications
where speed reduction is required but the use
of belt drives is unfeasible because of access or
maintenance requirements.
In flammable environments, fans are usually
constructed of nonferrous alloys to minimize the
risk of sparks caused by metal-to-metal contact. In
some applications, certain components of the fan
can be fabricated out of spark-resistant materials.
Fans that operate in flammable environments
should be properly grounded, including rotating
components, to minimize sparking because of stat-
ic discharge.
Temperature Range. To a large degree, temperature
range determines fan type and material selection.
In high-temperature environments, many materials
lose mechanical strength. The stresses on rotating
components increase as the fan’s operating speed
increases. Consequently, for high-temperature
applications, the fan type that requires the lowest
operating speed for a particular service is often
recommended. Radial blade fans can be ruggedly
constructed and are frequently used in

high-temperature environments. Component materials
also significantly influence a fan’s ability to serve
in high-temperature applications, and different
alloys can be selected to provide the necessary
mechanical properties at elevated temperatures.
Variations in Operating Conditions. Applications that
have widely fluctuating operating requirements
should not be served by fans that have unstable
operating regions near any of the expected
operating conditions. Because axial, backward-
inclined airfoil, and forward-curved fans tend to
have unstable regions, these fans are not recom-
mended for this type of service unless there is a
means of avoiding operation in the unstable
region, such as a recirculation line, a bleed fea-
ture, or some type of anti-stall device.
Space Constraints. Space and structural constraints
can have a significant impact on fan selection. In
addition to dimensional constraints on the space
available for the fan itself, issues such as mainte-
nance access, foundation and structural support
requirements, and ductwork must be considered.
Maintenance access addresses the need to inspect,
repair, or replace fan components. Because down-
time is often costly, quick access to a fan can pro-
vide future cost savings. Foundation and structural
requirements depend on the size and weight of a
fan. Selecting a compact fan can free up valuable
floorspace. Fan weight, speed, and size usually
determine the foundation requirements, which, in
turn, affect installation cost.
If the available space requires a fan to be located
in a difficult configuration (for example, with an
elbow just upstream or downstream of a fan), then
some version of a flow straightener should be
considered to improve the operating efficiency.
Because non-uniform airflow can increase the pres-
sure drop across a duct fitting and will degrade fan
performance, straightening the airflow will lower
operating costs. For more information, see the fact
sheet titled Configurations to Improve Fan System
Efficiency on page 39.
An important tradeoff regarding space and fan
systems is that the cost of floor space often
motivates designers and architects to configure a
fan system within a tight space envelope. One way
to accomplish this is to use small-radius elbows,
small ducts, and very compact fan assemblies.
Although this design practice may free up floor
space, the effect on fan system performance can be
severe in terms of maintenance costs. The use of
multiple elbows close to a fan inlet or outlet can
create a costly system effect, and the added
pressure drops caused by small duct size or a
cramped duct configuration can significantly
increase fan operating costs. System designers
should include fan system operating costs as a
consideration in configuring fan assemblies and
ductwork.
Fan Performance Curves
Fan performance is typically defined by a plot of
developed pressure and power required over a
range of fan-generated airflow. Understanding this
relationship is essential to designing, sourcing, and
operating a fan system and is the key to optimum
fan selection.
Best Efficiency Point. Fan efficiency is the ratio of
the power imparted to the airstream to the power
delivered by the motor. The power of the airflow is
the product of the pressure and the flow, corrected
for units consistency. The equation for total
efficiency is:
An important aspect of a fan performance curve
is the best efficiency point (BEP), where a fan
operates most cost-effectively in terms of both
energy efficiency and maintenance considerations.
Operating a fan near its BEP improves its
performance and reduces wear, allowing longer
intervals between repairs. Moving a fan’s operating
point away from its BEP increases bearing loads
and noise.
Another term for efficiency that is often used with
fans is static efficiency, which uses static pressure
instead of total pressure in the above equation.
When evaluating fan performance, it is important
to know which efficiency term is being used.
Total Pressure x Airflow
Total Efficiency =
bhp x 6,362
Where: Total Pressure is in inches of water
Airflow is in cubic feet per minute (cfm)
bhp is brake horsepower

A Sourcebook for Industry
Figure 1-1. Region of Instability5
7
Region of Instability. In general, fan curves arc
downward from the zero flow condition—that is,
as the backpressure on the fan decreases, the air-
flow increases. Most fans have an operating region
in which their fan performance curve slopes in the
same direction as the system resistance curve.
A fan operating in this region can have unstable
operation. (See Figure 1-1.) Instability results from
the fan’s interaction with the system; the fan attempts
to generate more airflow, which causes the system
pressure to increase, reducing the generated air-
flow. As airflow decreases, the system pressure
also decreases, and the fan responds by generating
more airflow. This cyclic behavior results in a
searching action that creates a sound similar to
breathing. This operating instability promotes poor
fan efficiency and increases wear on the fan
components.
Fan Start-Up. Start-up refers to two different issues
in the fan industry. Initial fan start-up is the
commissioning of the fan, the process of ensuring
proper installation. This event is important for
several reasons. Poor fan installation can cause
early failure, which can be costly both in terms of
the fan itself and in production losses. Like other
rotating machinery, proper fan operation usually
requires correct drive alignment, adequate
foundation characteristics, and true fit-up to
connecting ductwork.
Fan start-up is also the acceleration of a fan from
rest to normal operating speed. Many fans,
particularly centrifugal types, have a large rotation-
al inertia (often referred to as WR2), meaning they
require significant torque to reach operating speed.
5 Although fan system curves can have a static component, for the purposes of this sourcebook, system curves pass
through (0,0).
Slope Lines
2,000 4,000
3,000 13,000 15,000 17,00011,0005,000 7,000 9,000
6,000 8,000 10,000 12,000 14,000 16,000 18,000
Region of Instability
System
Curves
StaticPressure
(in.wg)
Airflow Rate (cfm)
Fan
Curve
26
24
22
20
18
16
14
12
10
8
6
4
2
In this region, the slopes of the fan curve
and the system curve are near parallel.
Instability results when the fan curve
intersects the system curve at more than one
point, causing the fan to hunt.

In addition to the WR2 load, the air mass moved
by the fan also adds to the start-up torque require-
ments on the fan motor. Although rotational inertia
is not typically a problem in heating, ventilation,
and air conditioning (HVAC) applications, it may
be a design consideration in large industrial appli-
cations. Proper motor selection is essential
in ensuring that the fan can be brought to its
operating speed and that, once there, the motor
operates efficiently.
Because the start-up current for most motors is 2
to 5 times the running current, the stress on the
motor can be significantly reduced by starting a
fan under its minimum mechanical load and
allowing the motor to achieve normal operating
speed more quickly than when under full load.
In many applications, system dampers can be
positioned to reduce the load on the fan motor
during start-up. For example, the power required
by a centrifugal fan tends to increase with increasing
flow (although in “non-overloading” fan types, the
power drops off after reaching a peak). In axial
fans, the power tends to decrease with increasing
flow. Consequently, for most centrifugal fan types,
large fan start-ups should be performed with
downstream dampers closed, while for most axial
fan types, start-ups should be performed with these
dampers open. However, there are exceptions to
these guidelines, and the actual power curve for
the fan should be evaluated to determine how to
soften the impact of a large fan start-up.
The power surges that accompany the starting of
large motors can create problems. Among the
effects of a large start-up current are power quality
problems and increased wear on the electrical sys-
tem. In response to increasing demand for equip-
ment that minimizes the problems associated with
large motor starts, electrical equipment manufac-
turers are offering many different technologies,
including special devices known as soft starters, to
allow gradual motor speed acceleration. A key
advantage of variable frequency drives (VFDs) is
that they are often equipped with soft starting fea-
tures that decrease motor starting current to about
1.5 to 2 times the operating current. Although VFDs
are primarily used to reduce operating costs, they
can significantly reduce the impact of fan starts on
an electrical system.
In axial fan applications, controllable pitch fans
offer a similar advantage with respect to reducing
start-up current. Shifting the blades to a low angle
of attack reduces the required start-up torque of
the fan, which allows the motor to reach operating
speed more quickly. For more information on
VFDs and controllable pitch fans, see the fact
sheet titled Controlling Fans with Variable Loads
on page 43.
System Effect. The system effect is the change in
system performance that results from the interaction
of system components. Typically, during the design
process, the system curve is calculated by adding
the losses of each system component (dampers,
ducts, baffles, filters, tees, wyes, elbows, grills,
louvers, etc.). The governing equation for pressure
loss across any particular component is:
The result of this equation is a parabolic line, as
shown by the system curve in Figure 1-2. This
system curve assumes all components display
pressure loss characteristics according to their loss
coefficients. However, in reality, non-uniform
airflow profiles that are created as the airstream
develops swirls and vortices cause system
components to exhibit losses that are higher than
their loss coefficients. The overall effect of these
added losses is to move the system curve up, as
shown by the corrected system curve in Figure 1-2.
The system effect can be minimized by configuring
the system so that the flow profile remains as
uniform as possible. However, if space constraints
prevent an ideal system layout, then system effect
consequences should be incorporated into the fan
selection process. For more information on how to
minimize losses, see the fact sheet titled Configurations
to Improve Fan System Efficiency on page 39.
V
∆p = C ( )
2
ρ
1,097
Where: ∆p = pressure loss in inches of water gage
(in. wg)
C = loss coefficient for the component
V = velocity in feet per minute
ρ = density of the airstream (0.075 pounds
per cubic foot at standard conditions)

Figure 1-2. System Effect for a Typical Fan and System
9
The system effect can be particularly problematic
when the airflow into or out of a fan is disrupted
into a highly non-uniform pattern. Poor configuration
of ductwork leading to or from a fan can severely
interfere with a fan’s ability to efficiently impart
energy to an airstream. For example, placing an
elbow close to the fan outlet can create a system
effect that decreases the delivered flow by up to
30 percent. This can require an increase in fan
speed, which in turn results in an increase in
power and a decrease in system efficiency.
Although underestimating the system effect
causes insufficient air delivery, many designers
overcompensate for it and other uncertainties
by selecting oversized fans. This practice creates
problems such as high energy costs, high mainte-
nance, and reduced system reliability. A more
reasonable approach is to combine proper system
layout practices with an accurate estimate of the
system effect to determine an appropriate fan size.
Fan System Components
A typical fan system consists of a fan, an electric
motor, a drive system, ducts or piping, flow control
devices, and air conditioning equipment (filters,
cooling coils, heat exchangers, etc.). An example
system is illustrated in a diagram on page 10.
To effectively improve the performance of fan
systems, designers and operators must understand
how other system components function as well.
The “systems approach” requires knowing the
interaction between fans, the equipment that
supports fan operation, and the components that
are served by fans.
Prime Movers. Most industrial fans are driven by
alternating current (AC) electric motors. Most are
induction motors supplied with three-phase,
240- or 480-volt power. Because power supplies
are typically rated at slightly higher voltages than
motors because of anticipated voltage drops in the
System Curve (with system effect)
System Curve
(as calculated)
Expected Performance
Actual Performance
Fan Curve
26
24
22
20
18
16
14
12
10
8
6
4
2
StaticPressure
(in.wg)
2,000 4,000
3,000 13,000 15,000 17,00011,0005,000 7,000 9,000
6,000 8,000 10,000 12,000 14,000 16,000 18,000
Airflow Rate (cfm)

distribution system, motors are typically rated at
230 or 460 volts. In recent years, because of
efforts by the National Electrical Manufacturers
Association (NEMA) and motor manufacturers, the
efficiency of general-purpose motors has signifi-
cantly improved. These improvements are also
attributable to the Energy Policy Act (EPAct), which
for most motors went into effect in October 1997.
To improve motor efficiency, motor manufacturers
have modified motor designs and incorporated
better materials, resulting in slight changes in
motor operating characteristics. Although initial
costs of the motors have increased 10 to 20 per-
cent, for high run-time applications, improvements
in motor efficiency create very attractive paybacks
through lower operating costs.
A characteristic of induction motors is that their
torque is directly related to slip, or the difference
between the speed of the magnetic field and the
speed of the motor shaft. Consequently, in many
fans, actual operating speeds are usually around
2 percent less than their nominal speeds. For
example, a theoretical four-pole induction motor
with no slip would rotate at 1,800 rpm with a
60-hertz power supply; however, rated operating
speeds for this motor are usually around 1,750 rpm,
indicating that slip rates are a little over 2.7 percent
at rated load. Fans that are driven by older motors
are probably operating at much lower efficiencies
and at higher levels of slip than what is available
from new motors.
Upgrading to a new motor can reduce operating
costs, because of improved motor efficiency, while
offering slightly improved fan performance. EPAct-
efficiency motors operate with less slip, which
means fans rotate at slightly higher speeds. For
applications that can effectively use this additional
output, this high efficiency can be attractive.
However, if the additional output is not useful, the
added power consumption increases operating costs.
Outlet Diffusers
Filter
Inlet Vanes
Centrifugal Fan
Belt Drive
Motor
Motor Controller
Heat Exchanger
Turning Vanes
(typically used on
short-radius elbows)
Variable Frequency Drive
Baffles
Figure 1-3. Example Fan System Components

Another component of the prime mover is the motor
controller. The controller is the switch mechanism
that receives a signal from a low power circuit,
such as an on/off switch, and energizes or de-ener-
gizes the motor by connecting or disconnecting
the motor windings to the power line voltage.
Soft starters are electrical devices that are often
installed with a motor controller to reduce the
electrical stresses associated with the start-up of
large motors. In conventional systems, the high
in-rush and starting currents associated with most
AC motors creates power quality problems,
such as voltage sag. Soft starters gradually
ramp up the voltage applied to the motor, reducing
the magnitude of the start-up current. As industrial
facilities increase the use of computer-based
equipment and control systems, soft starters are
becoming important parts of many motor control
systems. In fact, a major advantage associated with
most VFDs is that they often have built-in, soft-start
capabilities.
Another common characteristic of motors used in
fan applications is multiple speed capability.
Because ventilation and air-moving requirements
often vary significantly, the ability to adjust fan
speed is useful. Motors can be built to operate at
different speeds in two principal ways: as a single
set of windings equipped with a switch that ener-
gizes or de-energizes an additional set of poles, or
with the use of multiple windings, each of which
energizes a different number of poles. The first
type of motor is known as a consequent pole
motor and usually allows two operating speeds,
one twice that of the other. The second type of
motor can have two, three, or four speeds,
depending on application. In general, multiple-
speed motors are more costly and less efficient than
single-speed motors. However, the flow control
benefit of different motor speeds makes them
attractive for many fan applications.
Drive System. The drive system often offers
substantial opportunities to improve energy
efficiency and to lower overall system operating
costs. There are two principal types of drive systems:
direct drive and belt drive. Gear drives are also
used but are less common. In direct drive systems,
the fan is attached to the motor shaft. This is a
simple, efficient system but has less flexibility with
respect to speed adjustments.
Because most fans are operated with induction
motors, the operating rotational speeds of direct-
drive fans are limited to within a few percent of
the synchronous motor speeds (most commonly
1,200, 1,800, and 3,600 rpm). The sensitivity of
fan output to its operating rotational speed means
that errors in estimating the performance require-
ments can make a direct-drive system operate inef-
ficiently (unlike belt drives, which allow fan rota-
tional speed adjustments by altering pulley diame-
ters). One way to add rotational speed flexibility to
a direct-drive system is to use an adjustable speed
drive (ASD). ASDs allow a range of shaft speeds
and are quite practical for systems that have varying
demand. Although ASDs are generally not a prac-
tical option for fans that are only required to oper-
ate at one speed, ASDs can provide a highly effi-
cient system for fans that operate over a range of
conditions.
In axial fans, direct drives have some important
advantages. Applications with low temperatures
and clean system air are well-suited for direct
drives because the motor mounts directly behind
the fan and can be cooled by the airstream. This
space-saving configuration allows the motor to
operate at higher-than-rated loads because of
added cooling. However, accessibility to the motor
is somewhat restricted.
Belt drives offer a key advantage to fan systems
by providing flexibility in fan speed selection. If
the initial estimates are incorrect or if the system
requirements change, belt drives allow flexibility
in changing fan speed. In axial fans, belt drives
keep the motor out of the airstream, which can be
an advantage in high temperature applications, or
in dirty or corrosive environments.
There are several different types of belt drives,
including standard belts, V-belts, cogged V-belts,
and synchronous belts. There are different cost and
operating advantages to each type. In general,
synchronous belts are the most efficient, while
V-belts are the most commonly used. Synchronous
belts are highly efficient because they use a mesh-
type contact that limits slippage and can lower
operating costs. However, switching to synchronous
belts must be done with caution. Synchronous
belts usually generate much more noise than other
belts. They also transfer shock loads through the

drivetrain without allowing slip. These sudden
load changes can be problematic for both motors
and fans. Another problem with synchronous belts
is the limited availability of pulley sizes. Because
the pulleys have a mesh pattern, machining them
alters the pitch diameter, which interferes with
engagement. Consequently, pulleys are available
in discrete sizes, which precludes an important
advantage of belt drives: the ability to alter operating
rotational speeds by adjusting sheave diameters.
Because of these factors, synchronous belts are not
as widely used as V-belts in fan applications.
In contrast, V-belts are widely used because of
their efficiency, flexibility, and robust operation.
V-belts have a long history in industrial applications,
which means there is a lot of industry knowledge
about them. An important advantage to V-belts is
their protection of the drivetrain during sudden
load changes. Service conditions that experience
sudden drivetrain accelerations cause accelerated
wear or sudden failure. While synchronous belts
tend to transfer these shock loads directly to the
shafts and motors, V-belts can slip, affording some
protection. Although they are less efficient than
synchronous belts, V-belts offer many advantages
such as low cost, reliable operation, and operating
flexibility. In applications that use standard belts,
upgrades to V-belts should be considered.
Although they are not commonly used, gear systems
offer some advantages to belt systems. Gear systems
tend to be much more expensive than belt drive
alternatives; however, gears tend to require less
frequent inspection and maintenance than belts
and are preferable in applications with severely
limited access. Gears also offer several motor/fan
configurations, including in-line drives, parallel-
offset drives, and 90-degree drives, each of which
may provide an attractive advantage in some
applications. Gear-system efficiency depends largely
on speed ratio. In general, gear efficiencies range
from 70 to 98 percent. In large horsepower (hp)
applications (greater than 100 hp), gear systems
tend to be designed for greater efficiency because
of the costs, heat, and noise problems that result
from efficiency losses. Because gears require lubri-
cation, gearbox lubricant must be periodically
inspected and changed. Also, because gears—like
synchronous belts—do not allow slip, shock loads
are transferred directly across the drivetrain.
Ductwork or Piping. For most fan systems, air is
directed through ducts or pipes. In general, ducts
are made of sheet metal and used in low-pressure
systems, while pipes are sturdier and used in
higher-pressure applications. Because ducts are
used for most air-moving applications, “duct” will
be the common reference for this sourcebook; how-
ever, most of the same principles can be applied to
pipes.
In ventilation applications in which a fan pulls
directly from a ventilated space on one side and
discharges directly to an external space (like a
wall-mounted propeller fan), duct losses are not a
significant factor. However, in most applications,
ducts are used on one or both sides of a fan and
have a critical impact on fan performance. Friction
between the airstream and the duct surface is usu-
ally a significant portion of the overall load on a fan.
As a rule, larger ducts create lower airflow
resistance than smaller ducts. Although larger ducts
have higher initial costs in terms of material and
installation, the reduced cost of energy because of
lower friction offsets some of these costs and should
be included during the initial design process and
during system modification efforts. For more
information, refer to the fact sheet titled Fan
System Economics on page 55. Other considera-
tions with ducts are their shape and leakage class.
Round ducts have less surface area per unit cross
sectional area than rectangular ducts and, as a
result, have less leakage. In hot or cool airstreams,
this surface area also influences the amount of
heat transferred to the environment.
Duct leakage class, typically identified by the
factor CL (which has units of cfm/linear foot) is an
indicator of duct integrity. Variables that determine
CL include the type of joints used in construction,
the number of joints per unit length of duct, and
the shape of the duct. Depending on the length
of the duct system, leakage can account for a
significant portion of a fan’s capacity. This is
especially applicable to systems with rectangular
ducts that have unsealed joints. In many cases, the
system designer can improve the performance of
the ventilation system by specifying ducts that
have low CLs. For more information see the fact
sheet titled System Leaks on page 37.

Airflow Control Devices. Flow control devices
include inlet dampers on the box, inlet vanes at the
inlet to the fan, and outlet dampers at the outlet of
the fan. Inlet box dampers are usually parallel
blade dampers. Inlet vanes adjust fan output in two
principal ways: by creating a swirl in the airflow
that affects the way in which the air hits the fan
blades, or by throttling the air altogether, which
restricts the amount of air entering the fan. The
inlet vanes and dampers must be designed for
proper fan rotation and are to be installed in such
a way that these inlet vanes and dampers open in
the same direction as the fan rotation. The pre-
rotation or swirl of the air helps reduce the brake
horsepower of the fan. If the inlet dampers on the
inlet box are located too far away from the inlet of
the fan, the effect of pre-rotation may be lost or
reduced, and horsepower savings may be negligible.
The outlet damper, when used for controlling
airflow, is usually of opposed-blade design for better
flow distribution on the discharge side of the fan.
If the outlet damper is going to be used for open/
close service or for isolating the fan, a parallel-
blade discharge damper may be used. Typically,
fans with inlet vanes provide better power savings
while operating the fan at part load conditions, as
opposed to fans with inlet box dampers operating
in a similar situation. Inlet vanes provide better
controllability with optimum power savings
compared to other dampers. Outlet dampers adjust
resistance to airflow and move the operating point
along the fan’s performance curve. Because they
do not change air entry conditions, outlet dampers
do not offer energy savings other than shifting the
operating point along the fan horsepower curve.
Dampers can be used to throttle the air entering or
leaving a fan and to control airflow in branches of
a system or at points of delivery. Dampers control
airflow by changing the amount of restriction in an
airstream. Increasing the restriction creates a larger
pressure drop across the damper and dissipates some
flow energy, while decreasing the restriction reduces
the pressure differential and allows more airflow.
From a system perspective, proper use of dampers
can improve energy efficiency over traditional system
designs, especially in HVAC systems. In variable-air
volume (VAV) systems, dampers are effective at
rerouting airflow and at controlling the amount of air
delivered to a particular workspace. Because VAV
systems are much more energy efficient than their
precursors (constant-volume or dual-supply systems),
dampers can be used to lower system operating costs.
However, in many applications, dampers can
decrease fan efficiency. Dampers decrease total fan
output by increasing backpressure, which forces
the operating point of a fan to shift to the left along
its performance curve. Often, as the fan operating
point moves to the left along its curve, it operates
less efficiently and, in some cases, may perform in
an unstable manner. Unstable fan operation is the
result of an aerodynamic phenomenon in which
there is insufficient air moving across the fan blades.
The airflow rate surges back and forth resulting in
inefficient performance, annoying noise character-
istics, and accelerated wear on the fan drive system.
Another airflow control method that is available
for axial fan applications is the use of variable
pitch blades. Variable pitch fans control fan output
by adjusting the fan blade angle of attack with
respect to the incoming airstream. This allows the
fan to increase or decrease its load in response to
system demand. In effect, this method is similar to
that provided by inlet vanes, which adjust the
angle of attack of the entering airstream by creat-
ing a swirl in the airflow pattern. Variable pitch
fans provide a highly efficient means of matching
fan output to system demand.
Another method of airflow control is fan speed
adjustment. Recalling the fan laws, speed has a
linear relationship with airflow, a second-order
relationship with pressure, and a third-order
relationship with power. By slowing or speeding
up a fan, its output can be adjusted to match
system demand. In general, fan speed adjustment
is the most efficient method of airflow control.
There are two primary speed control options: mul-
tiple-speed motors and ASDs. Multiple-speed motors
have discrete speeds, such as “high,” “medium,”
and “low.” Although these motors tend to be
somewhat less efficient than single speed motors,
they offer simplicity, operating flexibility, a relative-
ly compact space envelope, and significant energy
savings for fan systems with highly variable loads.
ASDs include several different types of mechanical
and electrical equipment. The most common type

of ASD is a VFD. VFDs control the frequency of
the power supplied to a motor to establish its
operating speed. Unlike multiple speed motors that
operate at discrete speeds, VFDs allow motors to
operate over a continuous range of speed. This
flexibility provides accurate matching between fan
output and the flow and pressure requirements of
the system. For more information, see the fact
sheet titled Controlling Fans with Variable Loads
on page 43.
Air Conditioning and Process Equipment (Filters,
Heat Exchangers, etc.). Other equipment
commonly found in air-moving systems includes
devices used to condition the airstream to obtain
certain properties. Heat exchangers are used to
heat or cool an airstream to achieve a particular
temperature or to remove moisture. Filters are used
to remove unwanted particles or gases. Conditioning
equipment influences fan performance by providing
flow resistance and, in some cases, by changing air
density. Filters, including cyclone types or mesh
types, inherently create pressure drops, which are
often significant components of the overall system
pressure drop. Mesh-type filters create increasingly
large pressure drops as they accumulate particles.
In many systems, poor performance is a direct
result of inadequate attention to filter cleanliness.
Cyclone filters remove particulates by rapidly
altering the direction of the airflow so that heavy
particulates, unable to change direction quickly,
get trapped. Although cyclone filters are less
effective than mesh filters, they tend to require less
maintenance and have more stable pressure-drop
characteristics.
The effects of heating and cooling coils on fan
system performance depend largely on where in
the system the heat exchangers are located, the
extent of the temperature change, and how the
heat exchangers are constructed. Where there are
large changes in airstream temperature, fan per-
formance can change as the air density changes.
Heat exchangers that have closely spaced fins can
accumulate particulates and moisture that not only
impact heat transfer properties, but also increase
pressure losses.

The cost-effective operation and maintenance of a
fan system requires attention to the needs of both
individual equipment and the entire system. Often,
operators are so focused on the immediate demands
of the equipment that they overlook the broader
perspective of how the system parameters are
affecting this equipment. A “systems approach”
analyzes a system and how its components interact,
essentially shifting the focus from individual
components to total system performance. The
systems approach usually involves the following
types of interrelated actions:
■ Establishing current conditions and operating
parameters
■ Determining the present and estimating future
process production needs
■ Gathering and analyzing operating data and
developing load duty cycles
■ Assessing alternative system designs and
improvements
■ Determining the most technically and
economically sound options, taking into
consideration all of the subsystems
■ Implementing the best option
■ Assessing energy consumption with respect to
performance
■ Continuing to monitor and optimize the system
■ Continuing to operate and maintain the system
for peak performance.
The remainder of this section is a collection of 11
fact sheets that address both component and sys-
tem issues. Each fact sheet details a specific oppor-
tunity for improving fan system performance.
Performance Improvement Opportunity Roadmap
Section 2: Performance Improvement
Opportunity Roadmap
1—Assessing Fan System Needs
2—Fan Types
3—Basic Maintenance
4—Common Fan System Problems
5—Indications of Oversized Fans
6—System Leaks
7—Configurations to Improve Fan System Efficiency
8—Controlling Fans with Variable Loads
9—Fan Drive Options
10–Multiple-Fan Arrangements
11–Fan System Economics
Fact Sheets

1–Assessing Fan System Needs
There are three principal opportunities in the life
cycle of a system that can be used to improve fan
system performance:
■ During initial system design and fan selection
■ During troubleshooting to solve a system
problem
■ During a system capacity modification.
◆ Initial Fan Selection
Fan selection starts with a basic knowledge of system
operating conditions: air properties (moisture
content, temperature, density, contaminant level, etc.),
airflow rate, pressure, and system layout. These
conditions determine which type of fan—centrifugal
or axial—is required to meet service needs.
Axial fans move air along the direction of the fan’s
rotating axis, much like a propeller. Axial fans tend
to be light and compact. Centrifugal fans accelerate
air radially, changing the direction of the airflow.
They are sturdy, quiet, reliable, and capable of
operating over a wide range of conditions. Many
factors are used to determine whether axial or
centrifugal fans are more appropriate for certain
applications. A discussion of these factors is
provided in the Fan Types fact sheet on page 19.
After deciding which fan type is appropriate, the
right size must be determined. Fans are usually
selected on a “best-fit” basis rather than designed
specifically for a particular application. A fan is
chosen from a wide range of models based on
its ability to meet the anticipated demands of a
system. Fans have two mutually dependent outputs:
airflow and pressure. The variability of these
outputs and other factors, such as efficiency,
operating life, and maintenance, complicate the
fan selection process.
Tendency to Oversize. A conservative design tendency
is to source a fan/motor assembly that will be large
enough to accommodate uncertainties in system
design, fouling effects, or future capacity increases.
Designers also tend to oversize fans to protect
against being responsible for inadequate system
performance.
However, purchasing an oversized fan/motor
assembly creates operating problems such as excess
airflow noise and inefficient fan operation. The
incremental energy costs of operating oversized fans
can be significant. For more information on this
problem, see the fact sheet titled Indications of
Oversized Fans on page 33.
◆ Troubleshooting a System Problem
Some fan system problems, such as abnormally high
operating and maintenance costs and ineffective air-
flow control, are sufficiently troublesome to justify
a system assessment. If the system problems are
significant, then a change to the fan, its drive system,
or the airflow control devices may be justifiable.
High Operating and Maintenance Costs. Unusually
high operating costs are often caused by inefficient
fan operation that, in turn, can be the result of
improper fan selection, poor system design, or
wasteful airflow control practices. Improper fan
selection often means the fan is oversized for the
application, resulting in high energy costs, high
airflow noise, and high maintenance requirements.
Poor system design can lead to high operating
and maintenance costs by promoting poor airflow
conditions. For example, duct configurations that
create large system effect factors can cause
significant efficiency and airflow losses.
An effective way of minimizing maintenance and
operating costs is to keep a fan operating within a
reasonable range of its best efficiency point (BEP).
However, this practice is often difficult in systems
that have changing demands.
Poor Airflow Control. Poor airflow control refers to
a wide range of causes and problems, including
inadequate delivery to a system branch, surging
operation, and high airflow noise.
Inadequate delivery may be the result of poor
system balancing or leakage. If a branch has a
damper that is stuck open or a duct develops a
large leak, then this branch may provide a low
resistance flow path that robs airflow from other
delivery points. Fans typically react to this loss of
Assessing Fan System Needs
17

backpressure by generating high airflow rates.
In severe cases, many centrifugal fan motors will
overload if operated against little or no backpressure.
If not corrected, an overloaded motor will typically
shut itself down with thermal or current safety
switches.
Several situations can cause surging. Fans in a par-
allel configuration may be shifting load between
each other. A single fan may be operating in a stall
condition or hunting for the right operating point
along an unstable part of its performance curve. In
these cases, the system resistance is too high.
Electrical System Wear. Frequent start-ups of large
loads can add significant stress to an electrical
system. The in-rush current and the starting current
for motors can create voltage sags in the electrical
system and cause the motor to run hot for several
minutes. In fan applications where sensitive loads
can be affected by fan start-ups, the use of soft
starters should be considered. Soft starters are
electrical devices that gradually ramp up the
voltage to the fan motor, limiting the in-rush and
starting current. Soft starters can extend fan motor
life by keeping the motor temperature low.
Variable frequency drives (VFDs) are also com-
monly used to soft start fans. By gradually bringing
fan speed up to operating conditions, VFDs reduce
stress on the electrical system.
◆ System Capacity Change
For a system that is to be modified or upgraded, an
assessment of the available fan capacity should be
performed. Unless the existing fan is considerably
oversized, added capacity requires the installation
of a larger fan or an additional fan. Conversely, a
system with excess fan capacity can often be
accommodated by operating the fan at a slower
speed. In these applications, the effects of operating
a motor at less than half its rated load should be
considered. Recall that motor efficiency and power
factor fall significantly when the motor is operated
below half its rating.
Higher Fan Rotational Speed. One option to
accommodate the increased demand is to operate
the fan at a higher speed. In belt driven applications,
the sheave diameters can be changed to increase
fan speed. The relationship between fan speed and
airflow rate is linear; however, the relationship
between fan speed and power consumption is
cubed.
Consequently, increasing the airflow rate of the fan
by increasing its speed requires significantly more
power and may require a larger motor. The struc-
tural integrity of the rotating elements, bearings,
shafts, and support structure needs to be evaluated
for the higher speeds.
Lower Fan Rotational Speed. If the fan is oversized
for normal operating conditions, the feasibility of
operating it at lower rotational speeds should be
considered. Reducing fan speed can significantly
reduce energy consumption. For example, according
to the fan laws, reducing fan rotational speed by
20 percent decreases fan power by 50 percent.
Unfortunately, this speed reduction may cause
motor efficiency and power factor to drop to low
levels. The costs of inefficient operation and low
power factor may justify motor replacement or the
installation of a variable frequency drive.
Multiple Fans. Airflow rate can also be increased
by installing a separate fan next to an existing one.
Multiple-fan configurations have many advantages,
including flexibility in meeting widely varying
system demands and redundancy in case of equip-
ment failure. When adding a fan to an existing
system, the system can be configured so that both
fans operate concurrently or either fan operates
independently. The concurrent operation of two fans
creates a combined performance curve that may be
more appropriate for the system requirements than
that of a single fan. For more information, refer to
the fact sheet titled Multiple-Fan Arrangements
on page 51.
Fan Replacement. Replacing an existing fan with a
different model is also an option. Selecting a new,
larger fan requires consideration of the same factors
that are involved in any initial fan selection. A new
fan may be more feasible if the existing one has
degraded or requires extensive refurbishment. In
high run-time applications, the purchase of a new
fan with an energy-efficient motor may provide an
attractive payback.
1–Assessing Fan System Needs
RPMfinal
3
RPMinitial

2–Fan Types
◆ Basic Principle
Fans can be classified primarily into two different
types: axial and centrifugal. Axial fans act like
propellers, generating airflow along the direction
of the fan’s axis. Centrifugal fans generate airflow
by accelerating the airstream radially and convert-
ing the kinetic energy into pressure. Axial and cen-
trifugal fans have overlapping capabilities in terms
of pressure, airflow, and efficiency; however, usu-
ally they are not interchangeable.
Key impacts that determine which fan type is the
most appropriate include technical and non-
technical attributes. Technical considerations
include pressure, airflow rate, efficiency, space
constraints, noise generation, drive configuration,
temperature range, variations in operating conditions,
and tolerance to corrosive or particulate-laden
airstreams. Nontechnical reasons include cost,
delivery time, availability, and designer/operator
familiarity with a fan model.
Understanding the principles of fan selection can
be helpful in correcting poor system performance,
especially during retrofit or upgrade opportunities.
If noise levels, energy costs, maintenance require-
ments, or fan performance do not meet expectations,
then a different type of fan may need to be
considered.
◆ Centrifugal Fans
Centrifugal fans are the most commonly used type
of industrial fan. Centrifugal fans are capable of
generating high pressures with high efficiencies,
and they can be constructed to accommodate
harsh operating conditions. Centrifugal fans have
several types of blade shapes, including forward-
curved, radial-blade, radial-tip, backward-inclined,
backward-curved, and airfoil. Some centrifugal fan
types are capable of serving widely varying operating
conditions, which can be a significant advantage.
Forward-Curved Blades. This fan type, shown in
Figure 2-1, has blades that curve in the direction
of rotation. This fan type is typically used in
applications that require low to medium air
volumes at low pressure. It is characterized by
relatively low efficiency (between 55 and 65 percent).
This fan type can operate at relatively low speeds,
which translates to low levels of noise. Forward-
curved fans are commonly selected because of
their small size relative to other fan types.
Stress levels in fans are closely related to operating
speed; consequently, forward-curved fans do not
require high-strength design attributes. Their low
operating speed also makes them quiet and well-
suited for residential heating, ventilation, and air
conditioning (HVAC) applications. A typical per-
formance curve is shown in Figure 2-2. The dip in
the performance curve represents a stall region that
can create operating problems at low airflow rates.
Forward-curved fans are usually limited to clean
service applications. These fans are typically not
constructed for high pressures or harsh service.
Also, fan output is difficult to adjust accurately
(note how the fan curve is somewhat horizontal),
and these fans are not used where airflow must be
Fan Types
Figure 2-1. Forward-Curved Blade Fan
Rotation

2–Fan Types
closely controlled. Forward-curved fans have a
power curve that increases steadily with airflow
toward free delivery; consequently, careful driver
selection is required to avoid overloading the fan
motor.
Radial-Blade. Shown in Figure 2-3, this type is
commonly used in applications with low to medium
airflow rates at high pressures. The flat blade shape
limits material build-up; consequently, these fans
are capable of handling high-particulate airstreams,
including dust, wood chips, and metal scrap.
This fan type is characteristically rugged. The
simple design of these fans allows many small
metalworking shops to custom build units for special
applications. In many cases, the blades can be
inexpensively coated with protective compounds
to improve erosion and corrosion resistance. The
large clearances between the blades also allow
this fan to operate at low airflows without the
vibration problems that usually accompany operating
in stall. The characteristic durability of this fan
type is a key reason why it is considered an
industry workhorse.
Radial-Tip. This fan type fills the gap between
clean-air fans and the more rugged radial-blade
fans. Radial-tip fans are characterized by a low
angle of attack between the blades and the
incoming air, which promotes low turbulence. A
radial tip fan is shown in Figure 2-4.
Radial-tip fans have many of the characteristics of
radial-blade fans and are well-suited for use with
airstreams that have small particulates at moderate
concentrations and airstreams with high moisture
contents. Radial-tip fans can have efficiencies up
to 75 percent. These fans are commonly used in
airborne-solids handling services because they
have large running clearances. A typical fan curve
for radial fans is shown in Figure 2-5.
Backward-Inclined Fans. This fan type is character-
ized by blades that tilt away from the direction of
rotation. Within backward-inclined fans are three
different blade shapes: flat, curved, and airfoil. Flat
blade types, shown in Figure 2-6, are more robust.
Curved-blade fans tend to be more efficient. Airfoil
blades, shown in Figure 2-7, are the most efficient
of all, capable of achieving efficiencies exceeding
Figure 2-2. Forward-Curved Centrifugal Fan
Performance Curve
Fan Curve
Increasing Airflow
IncreasingPower
IncreasingPressure
Power Curve
Figure 2-3. Radial-Blade Centrifugal Fan
Rotation
Figure 2-4. Radial-Tip Centrifugal Fan
Rotation

2–Fan Types
85 percent. Because airfoil blades rely on the lift
created by each blade, this fan type is highly
susceptible to unstable operation because of stall.
A consequence of backward-incline blade orienta-
tion is a low angle of impingement with the
airstream. This promotes the accumulation of par-
ticulates on the fan blades, which can create per-
formance problems. Thin airfoil blades are more
efficient than the other blade types because of
their lower rotating mass. However, this thin-
walled characteristic makes this fan type highly
susceptible to erosion problems. Loss of blade
wall thickness can lead to cavity formation in
the blades, which can severely interfere with
fan performance.
A common application for backward-inclined fans
is forced-draft service. In these applications, the
fan is exposed to the relatively clean airstream on
the upstream side of the process. The high operating
efficiencies available from this fan type can provide
low system life-cycle costs. A typical performance
curve is shown in Figure 2-8. The motor brake
horsepower increases with airflow for most of the
performance curve but drops off at high airflow rates.
because of this non-overloading motor characteris-
tic, this fan type is often selected when system
behavior at high airflow rates is uncertain.
◆ Axial Fans
The key advantages of axial airflow fans are
compactness, low cost, and light weight. Axial
fans are frequently used in exhaust applications
where airborne particulate size is small, such as
dust streams, smoke, and steam. Axial fans are also
useful in ventilation applications that require the
ability to generate reverse airflow. Although the
fans are typically designed to generate flow in one
direction, they can operate in the reverse direction.
This characteristic is useful when a space may
require contaminated air to be exhausted or fresh
air to be supplied.
Axial fans have a severe stall region that makes
them particularly unsuitable for systems with
widely varying operating conditions. In this stall
region, airflow is insufficient to fill the blades,
causing the fan to operate unstably. The
consequences of unstable operation include
annoying noise patterns, inefficient performance,
Figure 2-5. Radial-Blade Fan Curve
Fan Curve
Increasing Airflow
IncreasingPower
Power Curve
Figure 2-6. Backward-Inclined Fan
Rotation
Figure 2-7. Backward-Inclined Centrifugal Airfoil Fan
Rotation
IncreasingPressure

2–Fan Types
and accelerated drivetrain wear. This problem of
stall can be solved in many axial fans by selecting
a fan with an anti-stall device. These devices alter
the airflow patterns around the fan blades, allowing
stable fan operation over the entire range of airflow
and pressure.
Axial fans must rotate faster than comparable
centrifugal fans to achieve the same airflow capacity.
This characteristic makes them noisier than
comparable centrifugal fans; however, the noise
signature is dominated by higher frequencies,
which are easier to attenuate.
Propeller Fans. The simplest version of an axial fan
is the propeller type, shown in Figure 2-9.
Propeller fans generate high airflow rates at low
pressures. Because propeller fans do not generate
much pressure, they are usually not combined with
extensive ductwork. Propeller fans tend to have
relatively low efficiencies, but they are inexpensive
because of their simple construction. Propeller fans
tend to be comparatively noisy, reflecting their
inefficient operation.
As shown in Figure 2-10, the power requirements
of propeller fans decrease with increases in airflow.
They achieve maximum efficiency, near-free deliv-
ery, and are often used in rooftop ventilation
applications.
Tubeaxial Fans. A more complex version of a
propeller fan is the tubeaxial fan. This type, shown
in Figure 2-11, is essentially a propeller fan placed
inside a cylinder. By improving the airflow
Figure 2-9. Propeller Fan Figure 2-11. Tubeaxial Fan
Figure 2-10. Propeller Fan Curve
Fan Curve
Increasing Airflow
Power Curve
IncreasingPressure
Airflow
Figure 2-8. Backward-Inclined Fan Curve
Fan Curve
Increasing Airflow
Power Curve
IncreasingPressure
IncreasingPower

2–Fan Types
characteristics, tubeaxial fans achieve higher
pressures and better operating efficiencies than
propeller fans.
Tubeaxial fans are used in medium-pressure, high-
airflow rate applications and are well-suited for
ducted HVAC installations. The airflow profile
downstream of the fan is uneven, with a large
rotational component. This airflow characteristic is
accompanied by moderate airflow noise.
Tubeaxial fans are frequently used in exhaust
applications because they create sufficient pressure
to overcome duct losses and are relatively space
efficient. Also, because of their low rotating mass,
they can quickly accelerate to rated speed, which
is useful in many ventilation applications.
The performance curve for tubeaxial fans is shown
in Figure 2-12. Much like propeller fans, tubeaxial
fans have a pronounced instability region that
should be avoided.
Tubeaxial fans can be either connected directly to a
motor or driven through a belt configuration.
Because of the high operating speeds of 2-, 4-, and
6-pole motors, most tubeaxial fans use belt drives
to achieve fan speeds below 1,100 revolutions per
minute.
Vaneaxial Fans. A further refinement of the axial
fan is the vaneaxial fan. As shown in Figure 2-13,
a vaneaxial fan is essentially a tubeaxial fan with
outlet vanes that improve the airflow pattern,
converting the airstream’s kinetic energy to pressure.
These vanes create an airflow profile that is
comparatively uniform.
Vaneaxial fans are typically used in medium- to
high-pressure applications, such as induced draft
service for a boiler exhaust. Like tubeaxial fans,
vaneaxial fans tend to have a low rotating mass,
which allows them to achieve operating speed
relatively quickly. This characteristic is useful in
emergency ventilation applications where quick air
removal or supply is required. Also, like other axial
fans, vaneaxial fans can generate flow in reverse
direction, which is also helpful in ventilation
applications. Depending on the circumstances,
these applications may require the supply of fresh
air or the removal of contaminated air.
Figure 2-13. Vaneaxial Fan
Airflow
Figure 2-12. Tubeaxial Fan Curve
Fan Curve
Increasing Airflow
Power Curve
IncreasingPressure
IncreasingPower
Figure 2-14. Vaneaxial Fan Curve
Fan Curve
Increasing Airflow
Power Curve
IncreasingPressure
IncreasingPower

2–Fan Types
Vaneaxial fans are often equipped with variable-
pitch blades, which can be adjusted to change the
angle of attack to the incoming airstream. Variable-
pitch blades can change the load on the fan,
providing an effective and efficient method of air-
flow control.
As shown in Figure 2-14, vaneaxial fans have
performance curves that have unstable regions to
the left of the peak pressure. These fans are highly
efficient. When equipped with airfoil blades and
built with small clearances, they can achieve
efficiencies up to 85 percent. Vaneaxial fans are
frequently connected directly to a motor shaft.

3–Basic Maintenance
◆ Maintenance Items
Common maintenance tasks on fan systems
include:
■ Periodic inspection of all system components
■ Bearing lubrication and replacement
■ Belt tightening and replacement
■ Motor repair or replacement
■ Fan cleaning.
The most costly consequence of improper
maintenance is unscheduled downtime. Causes of
this downtime vary according to the demands of
the application. Because each system places partic-
ular demands on its air-moving equipment, mainte-
nance requirements vary widely.
◆ Maintenance Schedules
To minimize the amount of unscheduled downtime,
basic system maintenance should be performed at
reasonable intervals, the length of which should be
determined by either hours of operation or calendar
periods. The maintenance interval should be based
on manufacturer recommendations and experience
with fans in similar applications.
Factors that should weigh into this schedule include
the cost of downtime, the cost and the risk of
catastrophic failure, and the availability of back-up
equipment. In systems that do not have abnormally
severe operating demands, a typical maintenance
schedule would include the items on the checklist.
Belt Inspection. In belt-driven fans, belts are usually
the most maintenance-intensive part of the fan
assembly. As belts wear, they tend to lose tension,
reducing their power transmission efficiency.
Even new, properly adjusted belts suffer losses of
5 to10 percent. As belt conditions degrade, these
losses increase. Because noise is one of the ways
in which the energy loss of belts is manifested,
poor belt condition can add significantly to the
ambient noise level.
Belt inspection is particularly important to the
operation of large fans because of the size of the
power losses. For example, in a 200-horsepower
(hp) fan, a 5 percent decrease in power transmis-
sion efficiency results in a 10-hp loss, translating
to $3,270 annually for a continuously operating
system.1
Basic Maintenance
Basic Maintenance Checklist
❏ Belts. Check belt condition, tightness, and
alignment. Also check sheave condition.
❏ Bearings. Determine bearing condition by
listening for noises that indicate excessive
wear, measuring bearing operating temperature,
or by using a predictive maintenance technique,
such as vibration analysis or oil analysis.
Lubricate bearings in accordance with fan
manufacturer instructions. Replace bearings,
if necessary.
❏ System Cleaning. Fans and system components
that are susceptible to contaminant build-up
should be cleaned regularly.
❏ Leaks. Check for ductwork leakage that can
lead to energy losses and poor system
performance.
❏ Motor Condition. Check the integrity of motor
winding insulation. Generally, these tests measure
insulation resistance at a certain voltage or
measure the rate at which an applied voltage
decays across the insulation. Also, vibration
analysis can indicate certain conditions within
the motor windings, which can lead to early
detection of developing problems.
1 Using $0.05/kilowatt-hour.

Although belt inspection and tightening is usually
a routine task for any mechanic, increased aware-
ness of the costs associated with poorly adjusted
belts can improve the attention devoted to this
maintenance effort.
In multiple-belt arrangements, whenever one belt
degrades to the point of requiring replacement, all
the belts should be replaced at the same time. As
belts wear and age, they exhibit different properties;
consequently, replacing only one or two belts in a
multiple-belt arrangement creates a risk of over-
loading one or more of the belts. Exposing all the
belts to roughly the same operating time mini-
mizes the risk of uneven loading.
Establishing proper belt tightness is essential to
minimizing the energy losses associated with belt
drives. However, care should be taken to prevent
overtightening the belts. This leads to high radial
bearing loads, accelerated wear, and shorter
bearing replacement intervals.
Fan Cleaning. In many fans, performance decline is
largely because of contaminant build-up on fan
blades and other system surfaces. Contaminant build-
up is often not uniform, resulting in imbalance
problems that can result in performance problems
and drivetrain wear. Because fans are often used in
ventilation applications to remove airborne con-
taminants, this problem can be particularly acute.
Fans that operate in particulate-laden or high-mois-
ture airstreams should be cleaned regularly.
Certain fan types, such as backward-inclined airfoil,
are highly susceptible to build-up of particulates or
moisture. These build-ups disturb the airflow over
the blades, resulting in decreased fan efficiency
and higher operating costs.
In high-particulate or moisture-content applications,
radial-blade, radial-tip, and forward-curved blade
type fans are commonly used because of their resist-
ance to contaminant build-up. If, for some other
reason, a different type of fan is used in a high-par-
ticulate or high-moisture service, then fan inspec-
tion and cleaning should be performed more fre-
quently than normal.
Leakage. System leaks degrade system performance
and increase operating costs. Leaks tend to develop
in flexible connections and in areas of a system
that experience high vibration levels. Leakage
decreases the amount of air delivered to the point
of service; consequently, one of the first steps in
troubleshooting a system that has experienced
declining performance is to check the integrity of
the ductwork.
Sources of leaks can be identified visually by
inspecting for poorly fitting joints, and tears or
cracks in ductwork and flexible joints. In systems
with inaccessible ductwork, the use of temporary
pressurization equipment can determine if the
integrity of the system is adequate. System pressure
checks are discussed in the fact sheet titled System
Leaks on page 37.
Bearing Lubrication. Worn bearings can create
unsatisfactory noise levels and risk seizure.
Bearings should be monitored frequently. Bearing
lubrication should be performed in accordance
with the manufacturer’s instructions. For example,
for high-speed fans in severe environments,
lubrication intervals can be necessary weekly or
more often.
■ For oil-lubricated bearings, check the oil quality
and, if necessary, replace the oil.
■ For grease-lubricated bearings, check the grease
quality and, if necessary, repack the bearings.
Be careful not to over-grease bearings as this
interferes with ball or roller motion and may
cause overheating.
■ Ensure the bearings are adequately protected
from contamination.
In axial fans, anti-friction bearings (ball, roller-type)
are predominantly used because of the need for a
robust thrust bearing to handle the axial thrust
load.
Motor Replacement. Even properly maintained
motors have a finite life. Over time, winding
insulation inevitably breaks down. Motors in
which the winding temperatures exceed rated
values for long periods tend to suffer accelerated
insulation breakdown. When faced with the
decision to repair or replace a motor, several
factors must be considered, including motor size,
motor type, operating hours, and cost of electricity.
For example, in a motor application where the

cost of electricity is $0.05/kilowatt-hour, the motor
operates 4,000 hours each year at 75 percent rated
load, and the rebuild cost is 60 percent of the price
of a new motor, the calculated breakeven point
between repair and replacement is 50 hp.2 Under
these circumstances, in applications requiring less
than 50 hp, replacement motors meeting Energy
Policy Act (EPAct) efficiency requirements should
be selected, while larger motors should be rebuilt.
Of course, each facility must establish its own
repair/replace strategy. There are several resources
that provide guidance in developing such a strategy.
A companion sourcebook, Improving Motor and
Drive System Performance: A Sourcebook for
Industry, discusses this issue in greater detail.
Other resources related to motor repair can be found
on the BestPractices Web site at www.oit.doe.gov/
bestpractices.
For motor rewinds, ensure that the repair facility
has a proper quality assurance program, because
poor quality motor rewinds can compromise motor
efficiency. Although motor rewinds are often
cost-effective, motors that have been previously
rewound can suffer additional efficiency losses
during subsequent rewinds. For more information
on motor repair, contact the Industrial Technologies
Information Clearinghouse at (800) 862-2086 or
the Electrical Apparatus Service Association (EASA)
at (314) 993-1269. (EASA is a trade association of
motor repair companies.)
For motor replacements, high-efficiency motors
should be considered. High-efficiency motors are
generally 3 to 8 percent more efficient than standard
motors. In high-use applications, this efficiency
advantage often provides an attractive payback
period. EPAct, which went into effect in October
1997, set minimum efficiency standards for most
general-purpose motors from 1 to 200 hp.
The MotorMaster+ software program can be a
valuable tool in selecting energy-efficient motors.
The program allows users to compare motors and
estimate energy costs and savings along with life-
cycle costs. Because MotorMaster+ contains motor
rotational speed data, it is useful in finding
replacement motors that operate at the same speed
as the existing motor. This can help avoid the
problem of installing a motor that, because of its
higher operating speed, causes the fan to generate
more airflow and consume more energy than the
previous motor/fan combination. MotorMaster+ is
available through the Industrial Technologies
Information Clearinghouse and can be downloaded
from the BestPractices Web site at
www.oit.doe.gov/bestpractices.
Fan Replacement. Under most conditions, fan blades
should last the life of the impeller. However, in harsh
operating environments, erosion and corrosion can
reduce fan-blade thickness, weakening the blades
and creating an impeller imbalance. In these cases,
either the impeller should be replaced or an entirely
new fan should be installed.
◆ Predictive Maintenance
In many applications, fan maintenance is reactive
rather than proactive. For example, bearing
lubrication is performed in response to audible
bearing noises. Fan cleaning is performed to
correct an indication of poor fan performance or
vibration because of dust build-up. Unfortunately,
many fan system problems remain unaddressed
until they become a nuisance, by which time they
may have resulted in significantly higher operating
costs.
Vibration analysis equipment is essentially a
refined extension of the human ear. By “listening”
to the vibrations of a motor or similar piece of
machinery, the instrumentation can detect the
early symptoms of a bearing problem, motor
winding problem, or dynamic imbalance. By
identifying problems before they become worse,
repairs can be effectively scheduled, reducing the
risk of catastrophic failure.
Fortunately, recent improvements in instrumentation
and signal analysis software have increased the
availability of vibration monitoring and testing
equipment. These devices can be permanently
installed with a fan and incorporated into an alarm
or safety shutdown system. Vibration monitors
offer relatively inexpensive insurance for avoiding
costly failures and can improve the effectiveness
with which fan maintenance is planned.
2 HorsePower Bulletin, Advanced Energy (in cooperation with the U.S. Department of Energy).

Portable vibration instruments can also be used as
part of a facility’s preventive maintenance system.
Vibrations measured during operation can be
compared against a baseline set of data, usually
taken when the machinery was first commissioned.
Vibration signatures taken at different points in a
fan’s operating life can be evaluated to determine
whether a problem is developing and, if so, how fast.
◆ Records
A written log or record documenting observations
and inspection results is a useful supplement to a
maintenance schedule. Often a machinery problem
will develop over time. A history of the repairs,
adjustments, or operator observations regarding
the conditions under which the problem becomes
noticeable improves the ability to effectively
schedule a repair. The MotorMaster+ software
contains an inventory module that allows the user
to record maintenance and inspection results.

4–Common Fan System Problems
◆ Basic Principle
Like most other rotating machinery, fans experience
wear and require periodic maintenance and repairs.
Dynamic surfaces in bearings and belt drives
degrade over time. Fan blade surfaces may erode
from abrasive particles in the airstream, and motors
eventually require replacement or rewinding.
Although some degree of wear is unavoidable,
operating the system at efficient levels reduces
the risk of sudden equipment failure and can
lower the cost and frequency of maintenance.
For more information, see the fact sheet titled
Basic Maintenance on page 25.
Fan system problems can be grouped into two
principal categories: problems that are related to the
fan/motor assembly and problems associated with
the system. A systems approach is important to
help understand the total costs and performance
impacts of these problems.
◆ Fan/Motor Assembly Problems
Problems with the fan/motor assemblies can
result from improper component selection, poor
installation, or poor maintenance.
Belt Drives. Belt drives are frequently the most
maintenance-intensive component of a fan/motor
assembly. Common problems include belt wear,
noise, and rupture. Belt wear can lead to efficiency
and performance problems. As belt slippage
increases, it can translate directly into lower fan
output. Insufficient belt tension can also cause
high noise levels through belt slap or slippage.
In some cases, belts will develop one or more
smooth spots that lead to vibrations during fan
operation.
In contrast, belt tension that is too high increases
the wear rate, increases load on the bearings, and
can create an increased risk of unexpected down-
time.
In multiple-belt drive assemblies, uneven loading
of the belts causes uneven wear, which can affect
the life and reliability of the whole drive unit.
Poor belt drive maintenance also promotes costly
system operation. Contaminant build-up on the
belts often results in increased slippage and noisy
operation. The presence of abrasive particles tends
to accelerate belt wear.
Belts are not the only item in a belt drive assembly
that develop problems. The sheaves themselves
are subject to wear and should be periodically
inspected. Because sheave diameter has a signifi-
cant effect on fan speed, the relative wear between
the driven and the driving sheave can affect fan
performance.
Bearings. As with most rotating machinery, the
bearings in a fan/motor assembly wear and, over
time, can create operating problems. To prevent
such problems from causing unplanned downtime,
bearings should be a principal maintenance item.
There are two primary bearing types in fan/motor
combinations: radial and thrust. In general, radial
bearings tend to be less expensive than thrust
bearings in terms of material cost and installation
requirements. Because of the nature of the airflow,
axial fans typically require heavier thrust bearings.
These bearings tend to be comparatively expensive,
making proper fan operation and effective
maintenance important.
Common bearing problems include noise, excessive
clearance, and, in severe cases, seizure. Because
operating conditions vary widely, the history of
other fans in similar applications should be used to
schedule bearing replacement. Vibration analysis
tools can improve confidence in determining
bearing condition and planning bearing work. In
oil-lubricated bearings, oil analysis methods can
help evaluate bearing condition.
Motors. Even properly maintained motors have a
finite life. Over time, winding insulation inevitably
breaks down. Motors in which the winding
temperatures exceed rated values for long periods
tend to suffer accelerated insulation breakdown.
In motor applications below 50 horsepower, the
Common Fan System Problems

common repair choice is simply to replace a
motor with a new one; however, in larger applica-
tions, rewinding an existing motor is often more
economically feasible. Although motor rewinds are
typically a cost-effective alternative, motors that
have been previously rewound can suffer addition-
al efficiency losses during subsequent rewinds.
For motor rewinds, ensure that the repair facility
has a proper quality assurance program, because
poor-quality motor rewinds can compromise motor
efficiency. For more information on motor repair,
contact the Industrial Technologies Information
Clearinghouse at (800) 862-2086, or the
Electrical Apparatus Service Association (EASA) at
(314) 993-1269. (EASA is a trade association of
motor repair companies.)
For motor replacements, energy-efficient motors
should be considered. A section of the national
Energy Policy Act (EPAct) setting minimum
efficiency standards for most common types of
industrial motors went into effect in October 1997.
EPAct should provide industrial end users with
increased selection and availability of energy
efficient motors. EPAct-efficient motors can be 3 to
8 percent more efficient than standard motors. In
high run-time applications, this efficiency advantage
often provides an attractive payback period.
The MotorMaster+ software program can be a
valuable tool in selecting energy-efficient motors.
The program allows users to compare motors and
estimate energy costs and savings along with life
cycle costs. It is available through the Information
Clearinghouse and can be downloaded from the
Web site at www.oit.doe.gov/bestpractices.
Contaminant Build-Up. Some fan types are susceptible
to contaminant build-up. The tendency to suffer
build-up is related to the velocity and angle of
attack of the airflow with respect to the blades.
In many cases, especially with backward-inclined
blades, this build-up can significantly affect fan
performance. Fan types that have blade shapes
that discourage material accumulation (for example,
radial and radial-tip types) are usually selected for
applications in which the airstreams have high
particulate or moisture content. However, even
in relatively clean air applications, over time,
particulate build-up can be a problem. Consequently,
fan cleaning should be a part of the routine
maintenance program.
In many heating and cooling system applications,
highly efficient fan types, such as backward-
inclined fans, are increasingly used to lower
system energy consumption. An important
component in this trend is the use of filters upstream
of the fans to lessen material build-up. While these
filters can help maintain efficient fan performance,
additional attention to filter cleaning and replace-
ment is required to avoid the pressure drops and
energy losses that result from clogged filters.
Fan Degradation. In airstreams that have corrosive
gases or abrasive particles, fan blade degradation
can present a threat to reliable operation. As fan
blades degrade, the airflow over the surfaces
becomes disrupted and the fan imparts energy less
efficiently to the airstream. Certain blade types are
particularly susceptible to erosion because of the
angle of attack with the airstream. In applications
where higher-than-expected blade degradation has
occurred, different fan types or fan materials should
be considered. Many fan manufacturers have
developed materials and coatings that solve this
problem.
◆ System Problems
Poor system performance can be caused by
several factors, including improper system design
and component selection, incorrect installation
practices, and inadequate maintenance. Improper
system design usually means the system is
configured so that it has high system effect factors
(SEFs) that result in high operating costs, system
leakage, and noisy system operation. Poor
component selection includes oversizing fans or
using ineffective or wasteful flow control devices.
Improper installation practices include on-site
modifications to the duct system that result in high
SEFs, improper fan rotational speed selection, and
incorrect fan rotation.
Inadequate maintenance often means a lack of
bearing lubrication and fan cleaning. Contaminant
accumulation on fan blades, duct surfaces, and in
filters results in decreased system efficiency and
inadequate airflow.
High Operating Costs. Many fan systems are designed
to support the highest expected operating loads.
Because systems are frequently not re-adjusted
during periods of low demand, fans often generate
higher-than-necessary airflows and incur

higher-than-necessary operating costs. Awareness
of the costs of inefficient system operation can
lead to efforts that reduce these costs and increase
system reliability. An important part of evaluating
whether operating costs can be significantly
reduced is to measure the amount of variability in
delivery requirements and determine operating con-
figurations that meet—but do not exceed—these
requirements.
Fouling. The accumulation of contaminants in
parts of a system can disrupt airflow profiles and
create high-pressure drops. Finned heat exchangers
and filters are particularly susceptible to contaminant
accumulation that can severely impair airflow. In
heat exchangers, fouling interferes with heat
transfer, which can compound an airflow problem
by requiring more airflow to compensate for the
reduction in heat exchanger effectiveness.
Consequently, fouling can have a compounding
impact on energy use.
Another aspect of fouling that can affect fan
performance is interference with inlet-guide vane
operation or blade-angle adjustment in variable-
pitch fans. Inlet-guide vanes are used to change
the load on a fan according to system airflow
requirements, thus allowing lower energy
consumption during periods of low demand.
However, because these devices are typically
controlled with a mechanical linkage, contaminant
build-up on the linkage components can impair
proper operation. Similarly, the linkages controlling
the position of variable-pitch blades can become
fouled with contaminant build-up, limiting
blade-angle adjustability.
Where contaminant build-up on mechanical
linkages is a problem, it can defeat the energy
savings and performance benefits that were intended
when the fan system was specified. Consequently,
either a greater maintenance effort should be made
to keep the linkage action free, or an alternative
airflow control solution should be considered.
In many dirty air fan applications, adjustable-speed
drives are attractive because of the avoided
fouling problems.
Airflow Noise. In many systems, airflow noise is a
large component of ambient noise levels. Improper
fan selection or operating a fan at higher speeds
than necessary can create avoidable noise levels
that impair worker comfort and productivity.
Insufficient Delivery. Poor system configuration can
lead to insufficient delivery. In many systems,
designers have improperly calculated the system
effect or have attempted to overpower it with
additional fan capacity. The system effect stems
from poor airflow conditions, and it can cause a
fan to operate much less efficiently. This causes a
system component to exhibit a higher-than-expected
pressure drop. Frequently, a key consequence of
the system effect is inadequate airflow.
There are many alternatives to compensate for this
problem. A common solution is to increase fan
speed, which increases airflow. Although this option
is sometimes unavoidable, it results in higher
operating costs and increased airflow noise.
Often, a more effective solution to inadequate
airflow can be obtained by addressing the
fundamental cause of the problem. By configuring
the system to improve airflow and by using flow
straighteners where appropriate, the performance
problems caused by the system effect can be mini-
mized. See the fact sheet titled Configurations to
Improve Fan System Efficiency on page 39.
Leakage. Some systems are constructed with little
attention to joint integrity. In these systems, leakage
can have a significant impact on operating cost
and system performance. Some system leakage is
unavoidable; however, minimizing the amount of
airflow and pressure loss can provide key savings.
Over time, system leakage tends to increase. This
is particularly true for systems with oversized fans.
Higher-than-expected system pressure and high
vibration levels cause joint integrity to suffer. As
joints loosen, the amount of leakage increases.
In systems with extensive ductwork, increases in
joint leakage can have a direct impact on airflow
delivery and can dramatically increase operating
costs. For more information, refer to the fact sheet
titled System Leaks on page 37.
Unstable Operation. Unstable operation can result
from operating certain types of fans at low airflow
rates and from the interaction of multiple fans
operating in parallel. In single fan configurations,
an aerodynamic phenomenon known as “stall”
occurs at low airflow rates. The severity of this
stall varies according to fan type, but is most
severe in axial fans, forward-curved centrifugal
fans, and backward-inclined centrifugal fans.

The hunting phenomenon associated with fan stall
occurs as the fan searches for a stable operating
point.
Stall occurs when there is insufficient air moving
across the fan blades. As the air “separates” from
the fan blade, the force on the blade changes,
causing the airflow to change as well. Stall hap-
pens largely because of air separation from the fan
blades. When this separation starts on one blade,
it often initiates an effect that carries over to the
next blade, resulting in a cascading effect.
The shape and distance between the fan blades
significantly affect how the stall affects fan perform-
ance. Some centrifugal fans, such as those with
radial blades, show little change in output. This fact
is largely because of the way radial-blade fans
operate—they do not rely on air slipping across
the blade surfaces and tend to have relatively large
distances between the blades. As a result, stall
problems are not as common in radial-blade fan as
they are in other fans.
Axial fans are particularly vulnerable to stall.
Because axial fans rely on the lift generated by blade
surfaces, stall can create a significant performance
problem. In general, axial fans are not recom-
mended for use in systems with widely varying
flow requirements, unless a means of keeping air-
flow rates above the stall point, such as a bleed
line or a recirculation path, is available.
A solution to this problem is commercially available.
A proprietary design feature, known as an anti-stall
device, automatically modifies the flow patterns
around the fan blades to provide stable operation
at all combinations of flow and pressure. In
applications where stall is a risk, this fan design
can be considered.
Even in systems in which operating conditions
are not expected to create stall problems, fan
degradation or a significant increase in system
pressure (filter clogging or system fouling) can
cause a fan to develop an instability problem. In
multiple-fan configurations, fans alternately shifting
loads between each other can cause instability.
This effect occurs at low-flow rates that are typically
to the left of the peak pressure on the combined
fan curve. Avoiding this problem requires
de-energizing one of the fans or decreasing the
system resistance to allow greater airflow. For
more information, refer to the fact sheet titled
Multiple-Fan Arrangements on page 51.

5–Indications of Oversized Fans
◆ Tendency to Oversize Fans
Conservative engineering practices often result in
the specification, purchase, and installation of fans
that exceed system requirements. Engineers often
include a margin of safety in sizing fans to
compensate for uncertainties in the design process.
Anticipated system capacity expansions and
potential fouling effects add to the tendency to
specify fans that are one size greater than those
that meet the system requirements.
A recent U.S. Environmental Protection Agency
(EPA) study revealed that within building fan sys-
tems, almost 60 percent of the fans were over-
sized, and almost 10 percent of the fans were
oversized by 60 percent1.
Unfortunately, many of the costs and operating
problems that result from oversized fans are
overlooked during the equipment specification
process. The problems that accompany the
selection of oversized fans are outlined below.
High Capital Costs. Large fans typically cost more
than small ones, and large fans also require larger
and more costly motors. Consequently, specifying
oversized fans results in higher-than-necessary
initial system costs.
High Energy Costs. Oversized fans increase system
operating costs both in terms of energy and main-
tenance requirements. Higher energy costs can
be attributed to two basic causes. The fan may
operate inefficiently because the system curve
intersects the fan curve at a point that is not near
the fan’s best efficiency point (BEP). Alternately,
even if an oversized fan operates near its BEP, by
generating more airflow than necessary, it uses
more energy and increases stress on the system.
Poor Performance. Oversized fans tend to operate
with one or more of the indications of poor
performance including noisy, inefficient, or unstable
fan operation. High airflow noise often results from
the excess flow energy imparted to the airstream.
In addition, oversized fans are more likely to
operate in their stall regions, which can result in
surging flow and vibrations that damage the fans
and degrade fan systems. Indications of stall
include pulsing airflow noise, system ducts that
seem to “breathe” in response to the pressure
variations, and vibrating fan and duct supports.
Frequent Maintenance. When oversized fans
operate away from their BEP, they may experience
cyclic bearing and drivetrain stresses. This is
particularly applicable when a fan operates in its
stall region, which is typically on the left side of the
fan performance curve. Also, cyclic bearing loads
tend to increase the stress on other drivetrain
components such as belts and motors. Oversized
fans also tend to create high system pressures,
which increase stress on the ductwork and
promote leakage.
High Noise/Vibration Levels. Fans that operate
inefficiently tend to create high airborne and
structure-borne vibration levels. Airborne vibra-
tions are often perceptible as noise, while structure-
borne vibrations are felt by the system equipment,
ductwork, and duct supports. Oversized fans often
create high airflow noise. Workers acclimate to
ambient acoustic levels and do not express
discomfort. However, high noise levels promote
fatigue, which reduces worker productivity.
High levels of structure-borne vibrations can create
problems in welds and mechanical joints over
time. High vibration levels create fatigue loads that
eventually crack welds and loosen fittings. In
severe cases, the integrity of the system suffers
and leaks occur, further degrading system
efficiency.
◆ Typical Indications of Oversized Fans
There are several indications of oversized fans. A
few of these indications can be discerned by quick
checks of system airflow control device settings.
Indications of Oversized Fans
1 ENERGY STAR® Buildings Upgrade Manual, U.S. EPA Office of Air and Radiation, 62021 EPA 430-B-97-024D, July 1997.

Systems in which airflow demand varies widely
inevitably require control devices to restrict airflow
for certain periods. However, in some systems,
inlet vanes and dampers remain closed so often
that they can be found rusted or locked in a
restrictive position. This indicates that the system
continually operates against an unnecessary load
and that fan operation is unnecessarily costly.
Other indications of oversized fans require more
detailed measurements. For example, the location of
the operating point on the fan curve can provide
an indication of how appropriately the fan is sized.
If possible, compare the pressure required by the
end uses to the pressure generated by the fan. If the
fan is oversized, it will generate more total pressure
for the same airflow than a correctly sized fan.
Fan Load Factor. As with any measured data, the
data’s usefulness is limited by how representative it
is of the average system operating conditions. In
systems with widely varying operating conditions,
simply taking data once will probably not provide
a true indication of system energy consumption.
To account for the fact that a fan does not operate
at a single condition all the time, an estimate of its
average load factor—the percentage of the fan’s
full capacity at which it operates—must be made.
Unfortunately, unless operators maintain
comprehensive records or are highly familiar with
fan operating data, the average load factor may be
difficult to determine.
Direct Measurement. An accurate way to determine
motor power consumption requires directly
measuring amps and volts. Kilowatt use is the
product of amps and line volts, corrected by the
power factor. Power factor is the ratio of real work
performed to the product of volts and amps. Motors
usually have power factors between 0.8 and 1,
because of the reactive power that they draw.
Reactive power is essentially the power stored in
the magnetic field of the motor. The power factor
data for most motors can be obtained from the
manufacturers.
When conditions permit, hot readings (readings
taken while the system is in operation) are relatively
simple to take. Using a clamp-type ammeter, the
current on each of the three power cables running
to the motor (most industrial motors are three-phase)
can be measured. Sometimes the motor controller
is a convenient point to take these readings, while
at other sites, the connection box on the motor is
more accessible. Line voltage is usually measured
at the motor controller and should be measured
around the same time as the current reading.
In some facilities, line voltage varies over time
because of changes in plant power consumption.
Alternately, for better accuracy, a power meter can
be used instead of separately reading volts and
amps. Most power meters measure real-time power,
obviating the need to estimate power factor. Direct
measurement of motor power is not always practical.
“Hot” measurement of a motor current exposes
workers to risk and may not be feasible in some
industrial environments because of high voltage or
exposure of the power connections to moisture or
contaminants. Such readings should only be taken
by properly trained personnel.
Use of Fan Curves. Another method of determining
fan power consumption is to measure the static
pressure generated by the fan and to determine
the corresponding brake horsepower as shown in
Figure 2-15. To determine electrical power, the
brake horsepower value must be divided by motor
efficiency. Also, the static pressure measurement
must be corrected for any difference between the
density of the airstream and the density used to
define the performance curve. Most fan perform-
ance curves assume air density of 0.075 pounds
per cubic foot, which is the density of air at
standard conditions. Also, because fan performance
is highly sensitive to operating speed, fan rotational
speed should be measured and the affinity law
Figure 2-15. Use of Fan Curve to Determine Power
Consumption
BHP
10
20
30
40
50
60
Power Curve
Fan Curve
StaticPressure(inwg)
2
4
6
8
10
12
14
16
18
20
22
24
26
2,000
4,000
6,000 10,000 14,000 18,000
8,000 16,000
Flow Rate (CFM)
12,000
Flow Rate (cfm)
bhp
StaticPressure(in.wg)

relationships should be used to find the equivalent
operating point on the performance curve.
Unfortunately, this method is the least accurate
and not usable on fans with relatively flat pressure
curves.
◆ Corrective Measures
In systems served by oversized fans, several
corrective measures can lower system operating
costs and extend equipment maintenance intervals.
Obviously, the entire fan/motor assembly could be
replaced by a smaller version or, if necessary, with
a more appropriate fan type; however, this option
may be too costly.
Other alternatives include:
■ Decreasing fan speed using different motor and
fan sheave sizes (may require downsizing the
motor)
■ Installing an adjustable speed drive (ASD)
or multiple-speed motor
■ Using an axial fan with controllable pitch
blades.
The choice among these measures depends on the
system and on the particular indicator that points
to the oversized fan problem.
Decreasing Fan Speed. Applications with an
oversized, belt-driven fan may be suitable for
decreasing fan speed. Fan power consumption is
highly sensitive to fan speed, as shown by the
following equation:
Consequently, significant energy savings are
available if the fan can adequately serve the system
at a lower speed. One method of reducing fan
speed is to adjust the ratio of the pulley diameters
for the motor and the fan.
A consideration in the fan-speed adjustment is
the effect on the motor. Most motors operate at
relatively consistent efficiencies above 50 percent
of full load capacity. There is some efficiency loss
above full load rating. However, below 40 percent
of the motor load, efficiency begins to decline. This
efficiency loss should be included in any economic
analysis. If fan power is to be reduced significantly,
a smaller motor should be considered.
Another consideration is the effect on the motor’s
power factor. At relatively low loads, the power
factor for a motor tends to decrease. Low power
factors are detrimental to a motor and its power
supply. Utilities often assess a charge against
industrial facilities that have low power factors. The
costs of reducing the motor’s power factor should
be included in the economic analysis and may
provide an incentive to switch to a smaller motor.
Another method of decreasing fan rotational speed
is to use a motor that has multiple speeds and to
select a lower rotational speed during low airflow
requirements. However, many of the same
advantages available from a multiple-speed motor
are also available from ASDs. ASDs, particularly
variable frequency drives (VFDs) are commonly
used as retrofit solutions because of their ability to
work with existing motors. Multiple-speed motors
are usually selected during the initial design
process rather than retrofitted into an existing sys-
tem.
Variable Frequency Drives. Fans that operate over a
wide range of their performance curves are often
attractive candidates for ASDs. The most popular
type of ASD is the VFD. VFDs use electronic con-
trols to regulate motor speed which, in turn,
adjusts the fan output more effectively than chang-
ing pulley diameters. The principal advantage
offered by VFDs is a closer match between the
fluid energy required by the system and the energy
delivered to the system by the fan. As the system
demand changes, the VFD adjusts fan speed to
meet this demand, reducing the energy lost across
dampers or in excess airflow.
Also, VFDs tend to operate at unity power factors,
which can reduce problems and costs associated
with reactive power loads. Because VFDs do not
expose mechanical linkages to potential fouling
from contaminants in the airflow, they can also
lead to reduced maintenance costs. The energy
and maintenance cost savings provide a return that
often justifies the VFD investment.
However, VFDs are not practical for all applications.
Fans with severe instability regions should not be
operated at rotational speeds that expose the fan to
inefficient operating conditions. Additionally, many
RPMfinal
3
RPMinitial

fans have resonant frequencies at speeds below
their normal operating speeds. Operating at these
resonant speeds can cause high vibration levels
that, if uncorrected, will cause damaging
vibrations. Because slowing a fan increases the risk
of encountering one of these conditions, a VFD, if
used, should be programmed to avoid operating at
these frequencies.
Also, for a belt-driven application where the fan
load is relatively constant, using a VFD simply to
slow the fan is probably less cost-effective than
using a sheave change-out. For more information,
see the fact sheet titled Controlling Fans with
Variable Loads on page 43.
Controllable Pitch Fans. Where the use of an axial
fan is practical, the selection of one with variable-
pitch fan blades can provide several advantages.
Controllable-pitch fans allow adjustment of the fan
blade angle of attack according to airflow require-
ments. Adjusting this angle of attack changes both
the load on the motor and the amount of energy
delivered to the airstream. The average operating
efficiencies of controllable pitch fans can equal or
exceed those achieved by VFD-powered fans.
Consequently, an application that requires an axial
fan to meet a peak load while normally operating
under much smaller load conditions may be an
attractive opportunity to use controllable-pitch
blades.
Advantages of controllable-pitch fans include
allowing the fan to operate over a wide range of
airflow requirements, reducing the start-up load on
the motor, and providing constant motor speed
operation. The disadvantages of controllable-pitch
blades include higher initial cost, exposure of the
pitch angle linkage to fouling, and the potential
efficiency and power factor effects that accompany
operating a motor below one-half of its rated
capacity.

6–System Leaks
◆ Basic Principle
Leakage is a common characteristic of most duct
systems. Because system leakage can be a signifi-
cant operating cost, it should be a consideration
during the design of a system and the selection of
a fan. The type of duct, the tightness and quality
of the fittings, joint assembly techniques, and the
sealing requirements for duct installation are all
factors that designers should consider during the
development of engineering drawings that guide
system installation. Failure to account for leakage
can result in an under-performing system. Also,
designers who focus on initial costs without con-
sidering the costs due to leakage can specify a sys-
tem that uses far more energy than necessary.
Leakage decreases the amount of delivered airflow.
Often, the costs of compensating for leakage in an
under-performing system far exceed the incremental
costs of installing a “tight” system or locating and
repairing a system leak.
System leakage tends to increase as the systems
age. Gaskets dry and lose their sealing properties,
and joints loosen from vibrations or inadequate
support (for example, sagging ductwork).
System leakage is also largely dependent upon the
pressure in the duct. One of the principal operat-
ing consequences of installing an oversized fan is
higher duct pressure, which increases the airflow
losses through leaks. The higher pressure in the
duct system is because of the damper throttling
that is required to achieve the proper flow rate. As
the dampers are throttled to create a higher pres-
sure loss, the system curve becomes steeper. The
higher pressure upstream of the dampers leads to
increases in leakage.
Costs of Leakage. The cost of leakage includes the
additional fan power required to generate more
airflow to compensate for leakage and, in some
applications, the power applied to cool, heat, or
filter that air. Much of the leakage cost is attributable
to the relationship between fan speed, fan power,
and the system curve. Under an assumption that
the system curve does not change because of the
leaks, a 5 percent increase in airflow would
require a 5 percent increase in fan speed and a 16
percent increase in power because of the fan law
relationship between fan speed and power. In real-
ity, the actual power required to generate this air-
flow is somewhat lower because the leakage
changes the system curve, allowing the fan to
operate against a lower backpressure. Consequently,
calculating the effect of leakage on fan power
requires analysis of the fan curve, the system
curve, and how the leaks affect the system curve.
However, the costs of leakage can include more
than just the fan power. In many industrial facilities,
particularly those that require precise environmental
control, the airflow delivered to the end uses is
often extensively conditioned. Relative humidity,
particulate content, and temperature must often be
kept within close tolerances. The leakage of air
that has been cleaned and conditioned generally
results in an increased load on heating, ventilation,
and air conditioning (HVAC) equipment, such as
chillers, dehumidifiers, etc.
Leakage Class. Leakage classes are denoted by
the term CL, which represents leakage in cubic feet
per minute (cfm) per 100 square feet of duct sur-
face area. CL factors range from 48 for unsealed
rectangular ducts to 3 for sealed, round ducts.
Different duct types have different leakage rates.
For example, because rectangular ducts have cor-
ners, the joints do not seal as well as those in
round ducts. Rectangular ducts also have more
surface area than round ducts with an equivalent
cross-section. The combined result of these factors
is that rectangular ducts tend to have higher leak-
age rates than round ducts.
To determine the correct leakage class in a duct
system, one must know how the ducts were
System Leaks

38
6–System Leaks
assembled. A CL of 48 is considered average for
unsealed rectangular ducts. Lower leakage classes
can be achieved depending on the pressure rating
and the construction techniques specified in the
assembly drawings. For example, if the transverse
joints in rectangular ducts are sealed, then the
estimated CL is reduced to 24 (12 for round ducts).
If all joints, seams, and wall penetrations are sealed,
then the leakage classes drop to 6 for rectangular
ducts (3 for round ducts).
The following equation forms the basis for the
leakage classes:
A useful resource for evaluating construction
techniques and leakage considerations of ventilation
ductwork is the Sheet Metal and Air Conditioning
Contractors’ National Association, Inc. (SMACNA).
Further information can be found in the HVAC Air
Duct Leakage Test Manual, which is referenced in
the Resources and Tools section on page 68.
Another useful resource is a standard maintained
by the American Society of Heating, Refrigerating,
and Air Conditioning Engineers (ASHRAE) titled,
ASHRAE 90.1, Energy Standard for Buildings
Except Low-Rise Residential Buildings, also
referenced on page 68. In an effort to promote
energy-efficient building design and construction
practices, this standard provides guidelines for
sealing ducts and test requirements for checking
leakage.
Fittings and Equipment. The tightness of system
fittings and equipment, such as access doors,
dampers, and terminal boxes, is also an important
consideration. Poorly constructed dampers or
improper sourcing of fittings promotes system
leakage. Designers should specify mating ductwork
and system equipment, so that joints fit tightly.
Also, where practical, designers should set
maximum allowable leakage rates for systems and
equipment, requiring integrity tests to verify that
the equipment is properly constructed and
installed.
Installation Practices. In addition to designing
systems to minimize leakage, installation personnel
should follow proper installation practices. Systems
should be sealed with the right type of sealant for
the application. Sealants that are compatible with
the service conditions, such as temperature and
moisture, should be selected. In general, because
there are essentially no adequate industry
performance standards for cloth and vinyl pres-
sure-sensitive tape, the tape is not recommended
for use on metal ducts. However, for flexible ducts,
the use of pressure-sensitive tape on metal duct
collars may be prescribed for the connection of
flexible duct materials to metal duct collars. This is
largely because of the ability of the tape to hold
well on clean, galvanized steel ducts and fittings.
Additionally, aluminum foil pressure-sensitive tape
may be specified for the connection of fibrous
glass duct to metal fittings (sleeves, terminals, and
other equipment), particularly where operating
pressures are 1 in. wg or less.
Tightness Tests. To ensure proper installation of
duct systems, tightness tests should be performed,
especially in systems where pressures exceed 2 or
3 in. wg. Although tightness checks are often not
feasible on every part of the system, as much of
the system as practical should be evaluated. In
general, tightness tests pressurize the duct up to its
pressure class rating and measure the airflow
required to sustain this pressure.
Q
CL =
p0.65
Where: Q = the leakage rate in cubic feet per
minute (cfm) per 100 square feet of
duct surface area
p = average of upstream and downstream
static pressure in inches of water gage
(in. wg) in the duct
Improving Fan System Performance

7–Configurations to Improve Fan System Efficiency
◆ Basic Principle
Flow patterns have a substantial impact on fan out-
put and system resistance. Fans and system com-
ponents are sensitive to the profile of an
entering airstream. Non-uniform air patterns cause
fans and system components to display flow/pres-
sure-drop characteristics that are different from the
manufacturer-supplied data. These differences are
attributable to the conditions under which the
manufacturer or an independent testing facility
tests their products. Lab conditions tend to create
uniform airflows. Consequently, performance data
that is gathered under ideal conditions will probably
not be repeated in an industrial environment. This
difference is the fundamental reason for including
the system effect.
The pressure drop across a component is calculated
by the equation:
The loss coefficient, C, is a dimensionless indicator
of flow resistance. The loss coefficient is based on
uniform flow into and out of the component.
However, under non-uniform flow conditions, the
coefficient becomes less accurate as an indicator.
Loss coefficients for system components such as
ducts, fittings, and components are typically listed
in tables provided by manufacturers. During the
system design phase, designers calculate system
resistance curves based on the published loss
coefficients for each component. However, system
configurations that promote non-uniform flow
conditions will create flow resistances that are
higher than anticipated, leading to under-performing
systems.
Unfortunately, a common approach to handling
uncertainties in system design is to increase the
size of the air movers, essentially overpowering
the problems associated with a system effect. The
consequences of this approach include high
equipment costs, high operating costs, increased
energy use, and noisy system operation.
◆ Design Practices
Many fan performance problems can be avoided
by designing the system so that the inlet and outlet
ducts to and from the fan are as straight as possible
within the physical constraints of the available space.
Inadequate attention to duct conditions during the
design phase increases operating costs. Designers
developing new systems and operators seeking to
upgrade or retrofit existing systems can minimize
system effect problems by recognizing and avoiding
common configurations that aggravate them.
Fan Inlet. Poor airflow conditions at the inlet of a fan
decrease the effectiveness and efficiency with which
a fan imparts energy to an airstream. In fact, this
sensitivity is used to control fan output in many types
of fans. Devices such as variable inlet guide vanes
adjust an airflow pattern entering a fan to change
the amount of flow energy transferred by the fan.
A pre-rotational swirl in the airflow rotates in the
same direction as a fan impeller. This phenomenon
reduces the load on the fan and shifts its performance
curve down and to the left. As shown in Figure 2-16,
these swirls can result from locating elbows too close
to a fan inlet. If possible, the fan should be config-
ured so that there is enough distance from the closest
bend for the airflow to straighten out. Because space
constraints often do not allow ideal configuration,
an airflow straightener, such as turning vanes, also
shown in Figure 2-16, can improve fan performance.
A counter-rotating swirl rotates in the opposite
direction of an impeller. This swirl creates an
additional load on the impeller. Although it tends
Configurations to Improve Fan System Efficiency
V
∆p = C ( )
2
ρ
1,097
Where: ∆p = pressure drop in inches of water gage
(in. wg)
C = local loss coefficient
V = velocity of the airstream in feet per
minute (ft./min.)
ρ = density of the airstream in pounds
per cubic foot (lbs./ft.3)

to shift a fan’s performance curve upwards, a
counter-rotating swirl is an inefficient method of
increasing fan pressure.
Another inlet condition that can interfere with fan
performance is highly non-uniform flow. As shown
in Figure 2-17, placing a bend too close to a fan
inlet can cause the airflow to enter the fan unevenly,
which leads to inefficient energy transfer and fan
vibrations. One general guideline is to provide a
straight duct length of at least 3 times the duct
diameter just prior to the fan inlet.
Fan Outlet. Poor outlet conditions also contribute
to under-performance in fan systems. Swirls and
vortices increase the pressure drops of elbows and
Figure 2-16. Pre-Rotational Swirl
Placing a fan close to an elbow
can create a pre-rotating swirl.
The use of turning vanes can
correct the swirl.
Impeller Rotation Impeller Rotation
Figure 2-17. Effect of Elbow Placement Close to a Fan Inlet
D
D
L
L
Placing a bend too close to a fan inlet can impair fan performance. General guideline: ensure L > 3D. If this
is not possible, the fan should be equipped with a factory inlet box.
Alternately, a flow straightener should be considered.

other duct fittings and can lead to inadequate
service to one or more system branches. As
shown in Figure 2-18, tees and other fittings
should be placed far enough downstream of
a fan for the airflow to become more uniform.
Similarly, where possible, fans should be oriented
so that the airflow profile out of a fan matches
the airflow behavior created by fittings such
as an elbow.
Also as shown in Figure 2-18, the outer radius of
an elbow requires higher velocity airflow than the
inside edge (because the airflow has farther to
travel), which is consistent with the airflow profile
leaving a centrifugal fan.
Airflow Straighteners and Splitters. Many problems
can be corrected with devices such as turning vanes
or airflow straighteners. For example, as shown in
Figure 2-19, flow splitters can prevent highly
Figure 2-18. Fan Outlet Conditions
Changing the configuration to
accommodate the air profile
improves system performance.
Placing the fan and the
downstream elbow such that the
airstream reverses the direction
creates a high loss through the
elbow and can impair fan
performance.
D
D
L
L
Make sure there is sufficient
distance between the fan and
the tee for the flow to
straighten out. If space
constraints make this
impossible, consider the use
of a flow straightener.
General guideline:
ensure L > 3D.

Figure 2-19. Effect of Placing a Tee Close to a Fan Inlet
disturbed airflow from forming in a tee. By properly
guiding the airstream into an adjoining duct, the
splitter avoids a highly disrupted airflow profile.
However, such devices should be used with caution.
For example, a non-uniform profile emerging
downstream of a tee can correct itself within several
diameter lengths of a straight duct. The use of flow
straighteners in this case may keep this imbalance
from correcting itself before the flow encounters
another component, thereby creating a problem
where one did not previously exist.
Duct Sizing. In most fan systems, friction between the
airstream and the duct surfaces accounts for most of
the energy consumed by the fan. The resistance of
airflow through a duct is a function of the square
of the velocity, as shown in the following equation:
The friction coefficient (ƒ) depends on the duct
surface finish, duct diameter, and the level of
turbulence in the airstream. Although accurately
calculating the pressure drop requires detailed
knowledge of the duct and airstream characteristics,
the relationship between pressure drop and duct
size is readily apparent. For a given delivery volume,
increasing duct diameter decreases both the velocity
and the friction loss per duct length. Consequently,
larger ducts create lower friction losses and lower
operating costs. For example, in a round duct,
doubling the duct diameter reduces frictional head
loss by a factor of 32. Although doubling the size of
a duct is often not realistic, increasing the diameter
of a round duct from 10 inches to 12 inches can
reduce friction head loss by 60 percent.
Offsetting the lower operating costs associated with
large ducts are higher initial costs, both in terms of
duct material and the added structural requirements.
Additionally, larger ducts take up more space, which
may be a problem for certain facilities. Also, some
material handling applications require a certain air
velocity to ensure proper entrainment, making
frictional head loss less important than system
performance. Striking the right balance between
these competing costs requires effort; however,
using a systems approach during the design phase
can minimize system life-cycle costs.
◆ Installation Practices
Frequently, installation of a fan system is performed
with inadequate regard to the effect of flow profile
on fan performance. Ductwork is often bent, shifted,
and dented on site to align connections and to make
room for other equipment.
When done far upstream or downstream of a fan,
these installation practices may have only a minor
impact on system performance; however, when
they create non-uniform flow into or out of a fan,
the effect can be costly. In fact, one of the first
checks typically performed on an under-performing
fan system is to examine the ductwork around the
fan to determine if it is creating the problem.
Placing the fan inlet too close to the tee can
impair fan performance.
If space constraints force a close gap, the use of a
splitter plate is recommended.
V
∆p = ƒ
L
( )
2
ρ
D 1,097
Where: ∆p = pressure drop (in. wg)
ƒ = non-dimensional friction coefficient
L = duct length in feet (ft.)
D = duct diameter (ft.)
V = velocity of the air stream (ft./min.)
ρ = density of the airstream (lbs./ft.3)

8–Controlling Fans with Variable Loads
◆ Basic Principle
Fans often serve over a wide range of operating
conditions. For example, many industrial ventilation
systems see variable loads because of changes in
ambient conditions, occupancy, and production
demands. To accommodate demand changes, flow
is controlled by three principal methods: inlet
vanes, outlet dampers, and fan speed control.
Each method has a set of advantages and draw-
backs in terms of initial cost, flow control effective-
ness, and energy efficiency. In fan systems that are
used relatively infrequently (for example, less than
500 hours annually), initial cost may be the
dominant factor. In high run-time applications,
flow control effectiveness and energy efficiency
may be the key determinants.
In many industrial applications, fans must operate
for extended periods. They are often used directly
to support production (material handling) or to
maintain safe working conditions (ventilation). In
either case, fan system operating efficiency is high
priority. The relative efficiencies of the flow control
options are shown in Figure 2-20. Although these
flow control options are available for new fan
selection, not all of them can be retrofit into exist-
ing fans. For example, controllable-pitch blades
are typically not considered for retrofits.
Many fans are sized to handle the largest expected
operating or peak condition. Because normal oper-
ating conditions are often well below these design
conditions, air-moving equipment is often oversized,
operating below its most efficient point and creating
several types of problems. Among these problems
are high energy costs, high system pressures and
flow noise, and, in systems with high particulate
contents, erosion of impeller and casing surfaces.
Consequently, the combination of extended
operating times and the tendency to oversize the
air-moving equipment creates a need for efficient
flow control. Often, the existing flow control
devices are inefficient, yet the costs associated
with their performance are not recognized.
Dampers. Dampers provide flow control by
changing the restriction in the path of an airstream.
As dampers close, they reduce the amount of flow
and increase pressure on their upstream side.
By increasing system resistance, dampers force
fans to operate against higher backpressure, which
reduces their output. As a fan works against higher
backpressure, its operating point shifts to the left
along its performance curve. Fans operating away
from their best efficiency points suffer increased
operating and maintenance costs.
Inlet Vanes. Inlet vanes are more commonly used
with centrifugal fans than axial fans. Inlet vanes
Controlling Fans with Variable Loads
Figure 2-20. Relative Power Consumption Among
Flow Control Options
120
100
80
60
40
20
20 40 60 80 100
Percent of Full Flow
PercentofFullLoadPower
OutletVanesDisc
Throttle
Controllable-Pitch Blades
SpeedControl
FanLaw
Inlet Vanes

change the profile of an airstream entering a fan.
Inlet vanes create swirls that rotate in the same
direction as a fan impeller. These pre-rotating swirls
lessen the angle of attack between the incoming
air and the fan blades, which lowers the load on
the fan and reduces fan pressure and airflow. By
changing the severity of the inlet swirl, inlet vanes
essentially change the fan curve. Because they can
reduce both delivered airflow and fan load, inlet
vanes can improve fan efficiency. Inlet vanes are
particularly cost effective when the airflow demand
varies between 80 and 100 percent of full flow;
however, at lower airflow rates, inlet vanes become
less efficient.
Disc Throttle. In some centrifugal fan designs, the
generated airflow can be controlled by changing
the effective width of the impeller using a sliding
throttle plate. As the plate moves, it changes the
amount of impeller width that is exposed to the
airstream. Although this fan design characteristic is
not common, its simple design may be feasible in
some applications.
Variable-Pitch Fans. An option with some types of
axial fans is the incorporation of a variable-pitch
feature for the fan blades. Variable-pitch fans allow
the fan blades to tilt, changing the angle of attack
between the incoming airflow and the blade.
Reducing the angle of attack reduces both the
airflow and the load on the motor. Consequently,
variable-pitch fans can keep fan efficiency high
over a range of operating conditions.
Variable-pitch fans can be a very efficient flow
control option and offer several performance
advantages. Because variable-pitch fans maintain
their normal operating speed, they avoid reso-
nance problems that can be problematic for cer-
tain fan types. Additionally, variable-pitch blades
can operate from a no-flow to a full-flow condition
without stall problems. During start-up, the fan
blades can be shifted to a low angle of attack,
reducing the torque required to accelerate the fan
to normal operating speed.
Disadvantages of this flow-control option include
potential fouling problems because of contaminant
accumulation in the mechanical actuator that
controls the blades. Also, because motor efficiency
and power factor degrade significantly at loads
below 50 percent of rated capacity, operating at
low loads for long periods may not provide
efficiency advantages and can incur a low power
factor charge from the utility.
Fan Rotational Speed Adjustments. Fan rotational
speed adjustments provide the most efficient
means of controlling fan flow. By reducing fan
rotational speed, less energy is imparted to the air-
stream, which means less energy must be dissipated
by the system airflow-control devices. There are
two primary devices used to control fan rotational
speed: multiple-speed motors and adjustable speed
drives (ASDs). Although both directly control fan
output, multiple-speed motors and ASDs typically
serve separate applications.
Multiple-speed motors contain a different set of
windings for each motor speed. For example, a
motor controller may have high, medium, and low
settings. Depending on the application, switching
from one discrete setting to another may provide a
sufficient level of speed control. Although they are
more expensive than single-speed motors, multi-
ple-speed motors provide a wide range of fan out-
put within a single unit, avoiding the need for mul-
tiple fans.
ASDs allow fan rotational speed adjustments over
a continuous range, avoiding the need to jump
from speed to speed as required by multiple-speed
fans. ASDs include several different types of
mechanical and electrical systems. Mechanical
ASDs include hydraulic clutches, fluid couplings,
and adjustable belts and pulleys. Electrical ASDs
include eddy current clutches, wound rotor motor
controllers, and variable frequency drives (VFDs).
VFDs are by far the most popular type of ASD,
largely because of their proven effectiveness in
reducing energy costs.
◆ Advantages of VFDs
For many systems, VFDs offer a way to improve
fan operating efficiency over a wide range of
operating conditions. VFDs also provide an
effective and easy method of controlling airflow.
Among the primary reasons for selecting VFDs are
improved flow control, ability to retrofit to existing
motors, their compact space advantages, and elim-
ination of the fouling problems associated with
mechanical control devices.

VFDs decrease energy losses by lowering overall
system flow. By slowing the fan and lessening the
amount of unnecessary energy imparted to the
airstream, VFDs offer substantial savings with
respect to the cost-per-unit volume of air moved.
When fan speed decreases, the curves for fan
performance and brake horsepower move toward
the origin. Fan efficiency shifts to the left, providing
an essential cost advantage during periods of low
system demand. Keeping fan efficiency as high as
possible across variations in the system’s flow
requirements reduces fan operating costs.
VFDs eliminate the reliance on mechanical
components, providing an attractive operational
advantage, especially in “dirty” airstreams.
Noise. Other benefits of VFDs include lower airflow
noise. Excess fluid energy is primarily dissipated in
the form of noise; consequently, operating a fan at
high capacity and then throttling the airflow tends
to generate high noise levels. Airflow noise can be
a significant component of the overall ambient
noise in a workplace. In fact, in many fan systems,
airflow noise is high enough to require ear protection.
Because VFDs decrease airflow noise during low sys-
tem demand, they can improve worker comfort.
Other System Benefits. VFDs offer operating
improvements by allowing higher fan operating
efficiency and by increasing system efficiency as
well. Using a system perspective to identify areas
in which fluid energy is dissipated in non-useful
work often reveals opportunities for operating cost
reductions. For example, in many systems, venting
flow does not noticeably affect the backpressure
on a fan. Consequently, in these applications, fan
efficiency does not necessarily decline during
periods of low flow demand. However, by analyzing
the entire system, the energy lost in venting excess
pressure or dissipating it across dampers can be
identified.
Another system benefit of VFDs is their soft-start
capability. During start-up, most motors experience
in-rush currents that are 5 to 6 times higher than
normal operating currents. In contrast, VFDs allow
the motor to be started with a lower start-up current
(usually about 1.5 times the normal operating
current), thus reducing wear on the motor windings
and the controller. Soft starting a fan motor also
provides a benefit to the electrical distribution
system. Large start-up currents can create voltage
sags that affect the performance of sensitive
equipment, such as controllers. By limiting start-up
current, VFDs can reduce these power quality
problems.
◆ Disadvantages of VFDs
Although VFDs offer a number of benefits in terms
of lower operating and maintenance costs, they
are not appropriate for all applications.
Decreasing the rotational speed of a fan too much
often risks unstable operation, especially with axial
fans and some centrifugal fans, such as backward-
inclined airfoil and forward-curved types. With
these fans, careful review of the performance
curves should precede the selection of a VFD.
Resonance. Fans, like most rotating machinery, are
susceptible to resonance problems. Resonance is
an operating condition in which the natural
frequency of some component coincides with the
frequency set up by the rotation. Fans are usually
designed so that their normal operating speeds are
not near one of these resonant speeds. However,
decreasing the rotational speed of a fan increases
the chances of hitting a resonant speed.
The effects of operating at resonant speeds can be
damaging. Depending on which component of the
assembly is in resonance with the fan rotational
speed, the vibrations can cause a wide range of
problems, from annoying noise to destructive fail-
ure. Shafts, bearings, and foundations are
particularly susceptible to problems with
resonance.
To avoid resonance problems, VFDs should be
programmed to avoid operating near resonant
speeds. This requires knowing what these resonant
speeds are, which, in turn, requires input from the
fan manufacturers. Similarly, programming the VFDs
accordingly often requires input from the VFD
manufacturers.
High Static Pressure. Another concern is the effect
of reducing fan speed in a system with high static
pressure. When a fan’s rotational speed is reduced,

the fan generates less pressure, and some fans, like
many types of turbomachinery, operate poorly
against shut-off conditions. For example, in many
fan systems, duct outlets are equipped with
normally closed dampers that require a certain
amount of static pressure to open them. If a VFD
slows the fan so that this static pressure require-
ment exceeds the pressure generated by the fan,
no airflow will be generated and the fan may
operate poorly.
Power Quality. In some VFD applications, power
quality can also be a concern. VFDs operate by
varying the frequency of the electric power
supplied to the motor. The solid-state switching that
accompanies inverter operation can create voltage
spikes that increase motor winding temperatures,
accelerating the rate of insulation degradation. To
account for the added winding heat, conventional
motors usually must be de-rated by 5 to 10 percent
when used with VFDs. A classification of motors
known as “inverter-duty” has been developed to
improve the matching of VFDs to motors.
VFDs can also generate electrical noise that
interferes with the power quality of the supporting
electrical supply. These problems are typically
correctable with the installation of coils or
electrical filters. Systems that are sensitive to minor
power supply disturbances should be served
separately from the VFD power supply.
VFD Efficiency. Finally, in some applications,
anticipated energy savings from VFDs are not
realized because of incomplete consideration of all
the losses associated with a VFD installation.
Although at full capacity VFDs can achieve effi-
ciencies of 98 percent, their efficiency at part-
loads is often much lower. When considering
VFDs, test data from the manufacturer should be
evaluated for the efficiencies at the actual load of
the application.
Although VFDs offer an attractive opportunity to
reduce energy consumption in many applications,
all of these considerations should be included in
any feasibility study or system analysis.

9–Fan Drive Options
Fans are typically driven by alternating current
(AC) motors. In industrial fan applications, the
most common motor type is the squirrel-cage
induction motor. This motor type is commonly
used because of its characteristic durability, low
cost, reliability, and low maintenance. These
motors usually have 2 or 4 poles which, on a 60-
hertz system, translates to nominal operating speeds
of 3,600 revolutions per minute (rpm) and 1,800
rpm, respectively. Although motors with 6 poles or
more are used in some fan systems, they are rela-
tively expensive. The most common class of
motors for fan applications is NEMA Design B.
Service factors range from 1.1 to 1.15, meaning
that the motors can safely operate at loads between
110 to 115 percent of their horsepower (hp) ratings.
Motors are connected to fans either directly, through
a gearbox, or, more commonly, by a belt system.
There are advantages and drawbacks to each drive
option. Understanding how drives are selected can
be helpful in correcting problems that are the
result of poor design.
◆ Direct Drives
Direct drives have several advantages over belt
drives, including higher efficiency, compact space
requirements, and lower maintenance. The
absence of a belt removes a key maintenance
element, allowing a fan to operate more reliably
and more quietly. Although belt drives are
occasionally used in fan applications over 300 hp,
they are rarely found in fan applications over
500 hp. At these power levels, the efficiency
advantages of direct drives are very attractive.
However, direct-drive fans must rotate at the speed
of the motor (typically 3,600 rpm, 1,800 rpm, or
1,200 rpm). This limits the applications for which
they can be used.
Direct drives may be used in applications where
space is an important consideration. For example,
vaneaxial fans are well-suited for direct-drive
applications because the motor often fits
conveniently behind the fan hub.
◆ Gear Drives
Gear drives are not as common as belt or direct
drives, but are useful in a few applications that
require special configurations between the fan
and motor. Gear systems have a wide range of
efficiencies that depend on gear design and speed
ratio. Gear systems can be very robust, affording
high reliability—a characteristic that is very
important in applications with restricted access to the
drive system. However, gears, unlike belt systems,
do not allow much flexibility in changing fan speed.
◆ Belt Drives
Because the required rotational speed of a fan is
usually less than 1,800 rpm, belts are used to
transfer power from a motor pulley (sheave) to a
fan pulley with a larger diameter. The desired fan
rotational speed can be achieved using various
pulley sizes according to the following relationship:
In small horsepower applications (typically less
than 5 brake horsepower), adjustable pitch sheaves
can be used. Because the diameter ratio is vari-
able, these configurations can provide speed control
advantages. However, most large industrial fan
applications use fixed diameter sheaves.
Types of Belt Drives. The four principal types of
belts are flat, V-belts, cogged V-belts, and synchro-
nous, each shown in Figure 2-21. Flat belts have a
uniform cross-section and transmit power through
friction contact with flat pulley surfaces. V-belts
are an improvement over the flat belt, using a
wedging action to supplement friction-based power
transfer.
Cogged V-belts offer the same advantages as V-belts;
however, their notched design provides additional
flexibility that allows the use of smaller pulleys.
Cogged V-belts are slightly more efficient than
conventional V-belts, because of their added
Fan Drive Options
Ddriver
RPMdriven = RPMdriver x
Ddriven

flexibility and the fact that the notched surface
transfers force more effectively.
Synchronous belts offer many advantages over
standard flat belts and V-belts. By using a mesh
engagement, synchronous belts are the most
efficient type of belt drive because they do not
suffer efficiency losses through slip. Synchronous
belts have teeth that engage with grooves in the
sheave. Synchronous belts can allow lower belt
tension than conventional belts, reducing the radial
loads on motor and fan bearings and extending
their operating lives. Further, synchronous belts do
not lose efficiency as they wear.
Despite their advantages, synchronous belts
must be used with caution. Synchronous belts
are very noisy, which often discourages their use.
Synchronous belts transfer torque very quickly
and, in applications with rapid load changes, the
cumulative effects of sudden acceleration and
deceleration increases wear on the driven machinery
and the risk of catastrophic failure. Synchronous
belts also require precise alignment, which is diffi-
cult to achieve in some fan applications. Before
selecting or switching to synchronous drives, one
should contact the belt drive vendor and review
the history of similar equipment in similar service
conditions.
Belt Sizing Considerations. The required belt
capacity must not only include the horsepower
required by the driven load; it must also account
for site-specific factors, such as temperature,
service factor, and arc of contact. The effect of
temperature varies according to the belt material.
Rubber contracts at higher temperatures.
Consequently, in belts that have high rubber
content, tension and stress increase as the drive
system temperature increases. Because temperature
also affects the mechanical strength of a belt, belts
should be sized to meet the torque requirements at
the highest normal operating temperature.
Ignoring the belt service factor and arc of contact
(see Table 2-1) can lead to undersizing the belts,
which may lead to frequent servicing or belt failure.
The belt service factor accounts for acceleration
loads during start-up and under load changes. For
most fans, the belt service factor is between 1.2
and 1.4. The arc of contact correction factor
accounts for the loss in power that results when
the belt runs over by less than 180° of the pulley
circumference. As shown in Table 2-1, the horse-
power rating drops off as the arc of contact
decreases. In applications where a small arc of
contact is unavoidable, the use of cogged V-belts
is recommended.
Belt Speed. The sensitivity of fan power to speed
makes belt-drive sizing an important issue.
Although flow rate is linearly related to fan speed,
power is related to the cube of fan speed. Even
changes in the slip of an induction motor can
create noticeable changes in the power transferred
to the airstream. Consequently, establishing the right
fan speed is critical to operating the system efficiently.
In general, fan-belt speed should not exceed
Figure 2-21. Different Types of Belts
Flat Belt V-Belt Cogged V-Belt Synchronous Belt Mesh Contact

6,500 feet per minute (ft./min.). Many manufacturers
suggest that to minimize bearing loads and to
increase reliability, up to but no more than
6,500 ft./min is a good speed value for belt system
design.
Maintenance Practices. Belt tension and alignment
should be checked periodically (see Figure 2-22).
Proper belt tension is typically the lowest that
prevents a belt from slipping at peak load. An
important maintenance practice to avoid is the use
of belt dressing. Belt dressing is a surface treatment
that increases the level of friction between a belt
and pulley. Because it masks the fundamental
cause of slippage, belt dressing only provides a
temporary means of reducing noise. Belt slippage
should be corrected by either cleaning the drive
system or adjusting belt tension.
When installing or replacing belts, ensure they are
oriented correctly in accordance with the directions
of the manufacturer. Belts are often tagged to show
the preferred direction of rotation. Although some
belts can be operated in either direction, belt
manufacturers often test their belts in one direction
and package them with an indication of this
direction.
In high-temperature applications, new belts should
be operated under low-load conditions and at normal
Table 2-1. Effect of Arc of Contact on V-Belt Horsepower Rating
Arc of contact
Figure 2-22. Proper Belt Tension
IncorrectCorrect
Rotation
Rotation
Loose belt indicated by excessive
slack on the drive side
Reasonable slack on the
non-drive side of the belt
Correction factor for
horsepower rating for a V-belt
according to arc of contact
180° 1
170° .98
160° .95
150° .92
140° .89
130° .86
120° .83
110° .79
100° .74
90° .69

operating temperature for a reasonable period. This
run-in time increases the creep strength of the belt.
Maximum Practical Speed Ratio. Most industrial fan-
belt drive applications are limited to speed ratios
below 4:1 (the motor speed is 4 times faster that
the fan speed); however, for small horsepower
applications (less than 1 hp), this ratio can be as
high as 10:1. The limiting factors on speed ratios
are the practical size of the pulleys, the arc of con-
tact between the belt and the drive pulley, and belt
speed.
Alignment. Proper belt installation requires careful
alignment and tensioning to ensure that belts wear
correctly. Belt alignment is important to minimize
side wear on the belt and to keep the stress on the
belt distributed evenly (see Figure 2-23). Side wear
on a belt will shorten its life; insufficient tension
promotes belt slippage, which can “polish” the
sheave surface as well as the contact surface of the
belt. A polished sheave surface has a low friction
constant, which reduces the belt’s ability to transfer
power. This loss is especially problematic after a
belt stretches, releasing tension and decreasing the
force holding the belt against the sheave.
◆ Other Considerations
Service conditions, such as high-temperature,
contaminants, erosive or corrosive properties, and
moisture, can preclude the exposure of motors to
the airstream. Motors can be sealed for protection
against the harmful effects of some airstreams;
however, these motors are more expensive and
sometimes require external cooling services.
Motor performance is closely linked to operating
temperature and, in high-temperature applications,
less heat from the motor windings is rejected to
the ambient air. High winding temperatures
decrease motor efficiency and accelerate the
degradation of winding insulation, shortening
motor life. In most severe system environments,
belt drives are used to allow the motor to operate
outside of the harmful service conditions.
Access. Access to a motor for maintenance and
repairs in a direct-drive fan assembly can also be
problematic. Because many direct-drive
applications are selected for space-saving reasons,
these motors are often located in tight spaces,
complicating tasks such as lubricating and replacing
bearings.
Figure 2-23. Improper Alignment
To avoid side wear and to evenly load a belt,
minimize these types of misalignments.

◆ Basic Principle
Fans can be combined in series or in parallel as an
alternative to using single, large fans. In many
cases, two smaller fans are less expensive and
offer better performance than one relatively large
one. Fans configured in series tend to be appropriate
for systems that have long ducts or large pressure
drops across system components. Fans used in an
induced-draft/forced-draft configuration can
minimize the amount of pressurization in a duct or
an enclosure. Advantages of fans in series include:
■ Lower average duct pressure
■ Lower noise generation
■ Lower structural and electrical support
requirements.
Fans placed in parallel can provide several
advantages including:
■ High efficiencies across wide variations in
system demand
■ Redundancy to mitigate the risk of downtime
because of failure or unexpected maintenance.
Parallel configurations may be feasible for systems
with large changes in air-moving requirements.
Wide variations in system demand preclude a
single fan from consistently operating close to its
best efficiency point (BEP). Operating a fan away
from its BEP can result in higher operating and
maintenance costs. Multiple fans placed in parallel
allow units to be energized incrementally to meet
the demands of the system. By energizing or
de-energizing individual fans to meet demand
changes, each fan can be operated more efficiently.
To allow operation of individual fans in a multiple-
fan arrangement, each fan must have a back-draft
damper installed to prevent recirculation through
the fan when it is idle.
Parallel fan configurations may also be a safety
requirement in case of a single fan failure. In
mining and other hazardous work environments,
ventilation is critical to worker safety. The
existence of backup fans can help avoid production
stoppages and may be a safety requirement.
◆ Advantages of Multiple-Fan Arrangements
Lower Average Duct Pressure. As shown in
Figure 2-24, the series-configurations fans along
different points in a system minimize the average
static pressure in a duct. Because leakage in a duct
system depends largely on the pressure difference
between inside and outside the system, reducing
the maximum system pressure can minimize energy
losses attributable to system leaks.
Lower Noise Generation. Lower pressure
requirements can decrease the noise generated by
fan operation.
Redundancy. Failure of one unit does not force a
system shutdown. In a single-fan application, a
repair task on that fan requires a system shutdown.
With a multiple-fan arrangement, one can be
repaired while the others serve the system. In some
facilities, fan failure can cause the interruption of
production work. With redundant fan configurations,
failure of one fan does not necessarily cause the
whole process to halt. Although total fan output
falls if one of the parallel units fails, the capacity
of the remaining fan or fans may be sufficient for
limited production.
Efficiency. Allowing each fan to operate close to its
BEP can provide substantial energy savings. In
addition, a potential advantage of multiple fans is
a higher overall efficiency level. Although larger
motors tend to be more efficient than smaller ones,
operating smaller, higher-speed fans close to their
BEPs can often achieve a net efficiency advantage
over a single, low-speed fan.
Structural and Electrical Constraints. Two smaller
fans in series may be more suitable in terms of
structural and electrical requirements than a single
one. Large motors have large starting currents that
can affect the power supply to other parts of the
facility. This concern is particularly acute if the
service requires the fan to energize and de-energize
Multiple-Fan Arrangements

relatively often. Frequent power surges that often
accompany the start-up of large motors can create
power quality variations that are problematic for
numeric controlled machinery and other sensitive
equipment.
Also, the use of multiple fans in parallel may be
necessary because of space considerations. A sin-
gle fan with an impeller large enough to move the
proper amount of air may not fit into the available
space or may encounter structural constraints.
◆ Potential Disadvantages of Multiple-Fan
Arrangements
When placing centrifugal fans in parallel, caution
should be used to ensure that one fan does not
dominate another. Ideally, all fans should be the
same type and size; however, differences in the
duct configuration can cause one fan to operate
against a higher backpressure. In severe cases, one
fan will force another fan to operate far away from
its BEP. Often, fans placed in parallel are the same
model so that there is balanced load sharing
during periods when all the fans are operating.
Another problem that accompanies parallel
operation of fans is instability. This problem is
especially applicable to fans with unstable operating
regions (axial fans, forward-curved centrifugal fans,
and airfoil fans). Instability results from alternate
load sharing that can occur below certain airflow
rates, as shown by the shaded region in Figure 2-25.
This can occur despite the fact that each fan alone
is operating outside of its stall region.
However, the combined performance curve of
both fans has a region in which there are multiple
combinations of airflow from each fan that can
Figure 2-24. Lower Duct Pressure Because of Fans Placed in Series
Average Pressure
System Resistance
System Resistance
Airflow
Airflow
Peak Pressure
Average Pressure
Peak Pressure
Distance Along Duct
Distance Along Duct
System Resistance
PressurePressure
Two Fans in Series
Single Fan

meet the system needs. The instability results
from the fans’ shifting between these multiple
combinations (known as “hunting”), as the fans
tend to load and unload. In addition to creating
an annoying noise pattern, this continued hunting
increases the wear on the fan drives because of
repeated acceleration and deceleration. To avoid this
problem, the system airflow should be kept to the
right of Point A, shown in Figure 2-25.
◆ Other Options
Other alternatives that can handle widely varying
operating conditions include multiple-speed fans,
variable frequency drives (VFDs), inlet vanes, and,
in the case of axial fans, controllable-pitch fan
blades. In each of these options, the airflow
generated by the fan is adjusted to meet the needs
of the system.
Multispeed motors have separate windings for
each speed. Operators can select different speeds,
such as high, medium, and low, according to the
system requirement. VFDs adjust fan speed by
changing the frequency of the power supplied to
the motor. VFDs allow speed control over a con-
tinuous range, which allows relatively accurate
matching between the system requirements and
fan operating speed. See the fact sheet titled
Controlling Fans with Variable Loads on page 43.
Inlet vanes control fan output by creating a swirl
in the airflow before it reaches the fan blades, thus
changing the angle of attack. This affects how much
energy is added to the airflow. Although this option
is generally less efficient than speed adjustment, it
is a relatively simple and inexpensive option that is
widely used.
In applications that use axial fans, controllable-
pitch fans should be considered to handle varying
airflow conditions. This fan type allows the fan
blades to tilt away from the incoming airflow. By
changing the angle of attack to the incoming air,
the amount of airflow generated and the load on
the motor can be controlled. This flow control
option is relatively efficient and offers several
advantages that are discussed in more detail on
page 43.
Figure 2-25. Instability Region Because of Parallel Operation of Identical Fans
Region of Instability
Single Fan Curve
Flow Rate (cfm)
A
2
4
6
8
10
12
14
16
18
20
22
24
2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000
17,00015,00013,00011,0009,0007,0005,0003,000
Combined Fan Curve

Fan systems are often critical in supporting plant
operations. A significant portion of all energy con-
sumed by motor-driven equipment in manufactur-
ing facilities is for process fans and air distribution.
In many industrial applications, fans help maintain
environmental conditions that ensure worker safety
and productivity by keeping machinery spaces cool.
Because they often directly support production
processes, many fans operate continuously. These
long run times translate into significant energy
consumption and substantial annual operating
costs.
The operating costs of large fans are often high
enough that improving fan system efficiency can
offer a quick payback. In spite of this, facility person-
nel often do not know the annual operating costs
of an industrial fan, or how much money they
could save by improving fan system performance.
Fan system operating costs primarily include
electricity and maintenance costs. Of these two
components, electricity costs can be determined
with simple measurements. In contrast, maintenance
costs are highly dependent on service conditions
and need to be evaluated case-by-case. A
particularly useful method of estimating these costs
is to review the maintenance histories of similar
equipment in similar applications.
◆ Load Factor
Fan economic analyses are primarily affected by
the amount of time and the percentage of full
capacity at which a fan operates. Because the fan
usually does not operate at rated full load all the
time, an estimate of its average load factor—the
average percentage of full load that a fan operates
over a period of time—must be made. Unfortunately,
unless operators maintain comprehensive records
or are highly familiar with fan operating data, the
average load factor may be difficult to determine.
A more accurate analysis of equipment operation
is the load-duty cycle. Load-duty cycle refers to the
amount of time that equipment operates at various
loads relative to its rated capacity and is often used
during the system design process. An example of a
load-duty cycle is shown in Figure 2-26. Load
factor can be determined from the load-duty cycle.
◆ Calculating Electricity Consumption
Electricity consumption can be determined by
several methods, including:
■ Direct measurement of motor current or power
■ Use of motor nameplate data
■ Use of performance curve data.
With any of these methods, the data’s usefulness is
limited by how representative it is of the average
system operating conditions.
Fan System Economics
Figure 2-26. Load-Duty Cycle
100
80
60
40
20
0
0 20 40
Percent of Full Load
PercentofOperatingHours
60 80 100

In systems with widely varying operating conditions,
simply taking data once will probably not provide
a true indication of fan energy consumption.
Nameplate Data. A quick way to determine energy
costs is to use the fan motor nameplate data. In
many applications, the fan/motor assembly is
oversized, which means the motor operates well
below its full-load nameplate data. However, by
using the nameplate data in combination with load
factor and power factor estimates, the fan’s annual
operating costs can be calculated. Other necessary
data include the annual hours of operation
(hours/year) and the average annual unit cost of
electricity ($/kilowatt-hour [kWh]).
Annual electricity costs can be calculated by
inserting this information into the equation found
in the Simple Calculation sidebar. This equation
assumes the electric motor driving the fan is
95 percent efficient (the 0.95 in the 1/0.95 factor),
which is a reasonable estimate for a fan motor
larger than 50 horsepower (hp). Newer motors
may have even higher efficiencies, thanks to the
Energy Policy Act, which has been in effect since
October 1997. If the fan uses an older motor that
has been rewound several times or has a smaller
motor, then a lower motor efficiency should be
used.
The motors used on most fans have a 1.15 contin-
uous service factor. This means that a motor with a
nominal nameplate rating of 100 brake horsepower
(bhp) may be operated continuously up to 115 bhp,
although motor efficiency drops slightly above the
rated load. Using nameplate data to calculate
energy costs on motors that operate above their
rated loads will understate actual costs.
Direct Measurement. A more accurate way to
determine electricity consumption requires taking
electrical measurements of both full-load amps
and volts. Motor full-load bhp and efficiency are
not required for this calculation. However, the
power factor over a range of operating conditions is
required. If practical, the power factor should be
measured with a power meter; however, if this
measurement is not feasible, then it can be
obtained from the motor manufacturer.
Using a clamp-type ammeter, the current on each
of the three power cables running to the motor
should be measured. The average of these three
readings should be used as the current value. This
is also an opportunity to determine if there are
phase imbalances.
Sometimes the motor controller is a convenient
point to take these readings while, at other sites, the
connection box on the motor itself is more accessi-
ble. Line voltage is usually measured at the motor
controller and should be measured around the
same time as the current reading. In some facilities,
line voltage drops with increased power usage.
Wattmeters, in general, are more difficult to use
because they require two simultaneous inputs,
voltage and current; many motor installations do
not offer convenient access to both. However, if
the use of a wattmeter is practical, then it would
provide a more accurate indication of actual
power consumption. Wattmeters provide a direct
reading of real power, obviating the need to
estimate power factor. Note that the direct
measurement of motor current is not always
practical. “Hot” measurement of motor voltage
exposes workers to risk and may not be feasible
in some industrial environments because of expo-
sure of the power connections to moisture or
contaminants. Such readings should only be taken
by properly trained personnel.
Simple Calculation
Annual electricity costs =
(motor full-load bhp) x (0.746 kW/hp) x
(1/efficiency) x (annual hours of operation) x (electricity
cost in $/kWh) x (load factor)
Assumptions:
• Cost of electricity = $0.05/kWh
• Load factor = 65 percent
• Motor efficiency = 95 percent
For example:
• Motor full-load bhp = 100 hp
• Annual hours of operation = 8,760 hours (3-shift,
continuous operation)
(100 hp) x (0.746 kW/hp) x (1/0.95) x (8,760 hours)
x ($0.05/kWh) x (0.65) = $22,356

The Direct Measurement sidebar shows an exam-
ple calculation of energy costs. By taking full-load
amps and volts, converting them to full-load
kilowatt (kW), multiplying by hours of operation
and electricity price, annual energy costs can be
determined.
Use of Fan Curves. Another method of determining
fan power consumption is to take pressure
measurements of the airstream and use the fan’s
performance curve to determine the corresponding
bhp. Refer to Figure 2-27. The correct method of
measuring fan pressure depends on how the fan is
configured in the system.
Figure 2-28 shows different methods of measuring
fan pressure. Once the fan operating pressure is
known, the corresponding horsepower reading can
be found. The Calculation with Fan Curves sidebar
shows how to estimate annual energy cost.
◆ Energy and Demand Charges—
Understanding Your Electricity Bill
The calculations shown previously use electricity
rates that are stated in terms of average dollars per
kWh ($/kWh). However, electric utilities bill
industrial customers using more complicated rate
structures. These typically include both energy
($/kWh) and demand charges ($/kW), and have
different rates depending on the level of
consumption or seasons. Demand charges are
Calculation with Fan Curves
Fan bhp/motor efficiency x (annual hours of operation)
x (electricity cost in $/kWh) x (load factor)
Assumptions:
• Fan discharge pressure is known
• $0.05/kWh unit electricity cost
For example:
• Fan discharge pressure = 19 in. wg
• Reading from the bhp line, fan bhp = 49
(49 bhp) x (0.746 kW/hp) x (1/0.9) x (8,760 hours)
x ($0.05/kWh) x (0.65) = $11,563
Direct Measurement Calculation
Case I. Separately using a voltmeter and an ammeter
(full-load amps) x (volts) x (1.732) x (power factor) ÷(1000)
x (annual hours of operation) x (electricity cost in
$/kWh) x (load factor)
Case II. Use of a Wattmeter
Wattmeter reading (using a 3-phase setting) x (annual
hours of operation) x (electricity cost in $/kWh) x (load
factor)
Assumptions:
• Cost of electricity = $0.05/kWh
• Power factor = 0.85
For example:
• Full-load amps = 115 amps
• Voltage = 460 volts
• Annual hours of operation = 8,760 hours (3-shift,
continuous operation)
(115 amps) x (460 volts) x (1.732) x (0.85)÷(1000) x
(8,760 hours) x ($0.05/kWh) x (0.65) = $22,172
Figure 2-27. Use of Fan Curve to Determine Power
Consumption
BHP
10
20
30
40
50
60
Power Curve
Fan Curve
StaticPressure(inwg)
2
4
6
8
10
12
14
16
18
20
22
24
26
2,000
4,000
6,000 10,000 14,000 18,000
8,000 16,000
Flow Rate (CFM)
12,000
bhp
Flow Rate (cfm)

based on the peak demand for a given month or
season and can have significant impacts on
electricity costs for some customers. When the
economic impacts of efficiency measures are
calculated, the actual cost of the electricity needs to
be considered, taking into account energy and
demand charges, seasonal rates, and different rates
for different levels of consumption.
◆ Maintenance Considerations and
Life-Cycle Costs
In addition to the cost of energy consumption,
maintenance costs can be a significant portion of a
fan system’s total operating costs. There are two
principal types of maintenance: preventive and
predictive. Both are intended to improve system
reliability, reduce the risk of unplanned downtime,
and avoid expensive failures. Preventive mainte-
nance generally refers to the use of a schedule to
perform inspections and replacement tasks.
Predictive maintenance uses diagnostic tools to
evaluate machinery condition, allowing effective
planning of repair or replacement tasks.
In much the same way that preventive and predictive
maintenance schedules minimize expensive
repairs, a well-designed system can avoid higher-
than-necessary operating costs. Using a life-cycle
cost perspective during initial system design or
during the planning of system upgrades and
modifications can provide both lower operating
costs and improved system reliability. For fan
applications, the dominant components of life-
cycle cost include initial equipment cost, energy
consumption, maintenance, and decommissioning.
A highly efficient fan system is not merely a system
with an energy-efficient motor. Overall system
efficiency is the key to maximum cost savings.
Often, users are only concerned with initial cost,
accepting the lowest bid for a component, while
ignoring system efficiency. To achieve optimum
fan system economics, users should select equip-
ment based on life-cycle economics and operate
and maintain the equipment for peak performance.
Figure 2-28. Alternative Methods of Measuring Fan Pressure
Inlet Total Pressure
Ducted Inlet and Outlet
Free Inlet – Ducted Outlet Ducted Inlet – Free Outlet
Fan Total Pressure Outlet Total Pressure
Static
Pressure
Total
Pressure
Total
Pressure
Static
Pressure

Industrial Technologies Program
and BestPractices
◆ Overview
Industrial manufacturing consumes 36 percent of
all energy used in the United States. The U.S.
Department of Energy’s (DOE) Industrial Technologies
Program assists industry in achieving significant
energy and process efficiencies. This program
develops and delivers advanced energy-efficiency,
renewable energy, and pollution prevention
technologies and practices for industrial applications.
Through an industry-driven initiative called the
Industries of the Future (IOF), Industrial Technologies
works with the nation’s most energy- and resource-
intensive industries to develop visions of their future,
along with roadmaps to achieve these visions over
a 20-year time frame. This collaborative process
aligns industry goals with federal resources to
accelerate research and development of advanced
technologies identified as priorities by industry.
The advancement of energy- and process-efficient
technologies is complemented by Industrial
Technologies’ energy management best practices
for immediate savings results. Through BestPractices,
Industrial Technologies assists the eight IOFs—
aluminum, chemicals, forest products, glass, metal
casting, mining, petroleum, and steel—in identifying
and realizing their best energy-efficiency and
pollution-prevention options from a system and life-
cycle cost perspective. Through activities such as
plant-wide energy assessments, implementation of
emerging technologies, and energy management of
industrial systems, BestPractices delivers energy
solutions for industry that result in significant energy
and cost savings, waste reduction, pollution pre-
vention, and enhanced environmental performance.
◆ Plant Assessments
Depending on the industry, energy can account for
10 percent or more of total operating costs. Energy
assessments identify opportunities for implementing
new technologies and system improvements. Many
recommendations from energy assessments have
payback periods of less than 18 months and can
result in significant energy savings.
■ Plant-wide energy assessments help manufacturers
develop comprehensive plant strategies to
increase efficiency, reduce emissions, and boost
productivity. Annual competitive solicitations
offer a 50 percent cost share of up to $100,000
in matching funds.
■ Small- to medium-sized manufacturers can
qualify for free assessments from university-
based Industrial Assessment Centers.
◆ Emerging Technologies
Emerging technologies are those that result from
research and development and are ready for full-
scale demonstration in real-use applications.
Industrial Technologies recognizes that companies
may be reluctant to invest capital in these new
technologies, even though they can provide signifi-
cant energy and process improvements. However,
through technology implementation solicitations,
Industrial Technologies helps mitigate the risk
associated with using new technologies that are
supported by IOF partnerships. By sharing
implementation and providing third-party validation
and verification of performance data, the energy,
economic, and environmental benefits can be
assessed to accelerate acceptance of new technologies.
◆ Energy Management
Industrial Technologies encourages manufacturers
to adopt a comprehensive approach to energy use
that includes assessing industrial systems and
evaluating potential improvement opportunities.
Efficiency gains in compressed air, motor, process
heating, pumping, and steam systems can be
significant and usually result in immediate energy
and cost savings. The program offers software tools
and training in a variety of system areas to help
industry become more energy and process efficient,
reduce waste, and improve environmental
performance.
Programs, Contacts, and Resources
Section 3: Programs, Contacts, and Resources

◆ Allied Partnerships
Allied Partners are manufacturers, associations,
industrial service and equipment providers,
utilities, and other organizations that voluntarily
work with Industrial Technologies. Allied Partners
seek to increase energy efficiency and productivity
within industries by participating in, endorsing, and
promoting Industrial Technologies programs,
products, and services. Allied Partnerships help the
program achieve industrial energy efficiency goals
by extending delivery channels through the
partners’ existing networks. In turn, partners benefit;
they achieve their own corporate, institutional, or
plant goals and objectives by expanding services
to customers and suppliers. Allied Partners also
gain access to technical resources, such as soft-
ware, technical publications, and training, and can
gain recognition as leaders in the implementation
of energy-efficient technologies and practices.
Allied Partners who successfully complete training
and a qualifying exam in the use of Industrial
Technologies software tools are recognized as
Qualified Specialists. For more on Allied Partner-
ships, contact the Industrial Technologies
Information Clearinghouse at (800) 862-2086.
◆ Technical Resources
Industrial Technologies offers a variety of resources
to help industry achieve increased energy and
process efficiency, improved productivity, and
greater competitiveness.
Industrial Technologies Information Clearinghouse.
The Clearinghouse fields questions on products and
services including those focused on the IOFs. They
can also answer questions about industrial systems,
such as compressed air, motors, process heating,
and steam. The Clearinghouse can be the first stop
in finding out what’s available from Industrial
Technologies. Contact the Clearinghouse at
(800) 862-2086 or at clearinghouse@ee.doe.gov.
Industrial Technologies and BestPractices Web Sites.
The Industrial Technologies and BestPractices Web
sites offer an array of information, products, and
resources to assist manufacturers who are interested
in increasing the efficiency of their industrial
operations. Users can gain access to Web pages for
the eight IOFs, learn about upcoming events and
solicitations, and much more through the Industrial
Technologies Web site at www.oit.doe.gov.
The BestPractices Web site offers case studies of
companies that have successfully implemented
energy-efficient technologies and practices,
software tools, tip sheets, training events, and
solicitations for plant assessments. Find these and
other resources at www.oit.doe.gov/bestpractices.
Software Tools and Training. Industrial Technologies
and its partners have developed several software
tools for systems improvements to help users make
decisions for implementing efficient practices in
theirmanufacturing facilities. Tools for assessing the
efficiency of fan and process heating systems are
in development and will be ready in the near
future. The following software tools are currently
available.
• AirMaster+ provides comprehensive information
on assessing compressed air systems, including
modeling, upgrades to existing and future systems,
and evaluating savings and effectiveness of
energy-efficiency measures.
• MotorMaster+ 3.0 software is an energy-efficient
motor selection and management tool that
includes a catalog of more than 20,000 AC motors.
Version 3.0 features motor inventory manage
ment tools, maintenance log tracking, efficiency
analysis, savings evaluation, energy accounting,
and environmental reporting capabilities.
• The Pumping System Assessment Tool (PSAT)
helps industrial users assess the efficiency of
pumping system operations. PSAT uses achievable
pump performance data from Hydraulic Institute
standards and motor performance data from the
MotorMaster+ database to calculate potential
energy and associated cost savings.
• The Steam System Assessment Tool (SSAT) is
The Steam System Assessment Tool (SSAT) allows
users to assess potential savings from individual-
ized steam-system improvements. Users input
data about their plant's conditions, and the SSAT
generates results detailing the energy, cost, and
emissions savings that various improvements
could achieve.
• The Steam System Scoping Tool is designed to
help steam system energy managers and
operations personnel for large industrial plants.
This spreadsheet program profiles and grades

steam system operations and management. This
tool will help users evaluate steam system
operations against identified best practices.
• The 3E Plus software tool allows users to easily
determine whether boiler systems can be
optimized through the insulation of boiler steam
lines. The program calculates the most economical
thickness of industrial insulation for a variety of
operating conditions. Users can make calculations
using the built-in thermal performance relation-
ships of generic insulation materials or supply
conductivity data for other materials.
Training sessions in industrial systems improvements
using these software tools are offered periodically
through Allied Partners. For more information,
visit the BestPractices Web site at www.oit.doe.
gov/bestpractices.
Energy Matters Newsletter. Energy Matters, published
quarterly, is Industrial Technologies technical news-
letter. Articles include case studies of companies
that have successfully implemented energy-efficient
technologies and practices, optimization tips for
improving system operations, technology updates,
Allied Partner activities, and news and information
on plant assessments, system improvements, and
new products and services. For a free subscription
to Energy Matters, contact the Information
Clearinghouse or subscribe online at www.oit.doe.
gov/bestpractices/energymatters/energy_matters.shtml.
◆ Benefits of Participation
BestPractices is only as effective as its partners.
Industrial plant efficiencies can only be improved
when plant engineers, plant managers, service
providers, and industry leaders get involved. All of
these people can participate in and benefit from
BestPractices in the following ways.
End Users. End users have access to the broad
variety of BestPractices tools described earlier in this
section, and also have access to the Industrial
Technologies Information Clearinghouse. The
technical staff at the Clearinghouse can answer spe-
cific questions about energy efficiency upgrades
and assessments. They are available Monday
through Friday from 9 a.m. to 8 p.m., Eastern
Standard Time. Call (800) 862-2086 or e-mail
clearinghouse@ee.doe.gov.
End users can participate in plant-wide energy
assessments. Depending on the size of the facility,
BestPractices offers no-cost or cost-shared energy
assessments with a team of experts. Small- to
medium-sized plants may be eligible for a no-cost
assessment with one of our Industrial Assessment
Centers. Larger plants can propose a cost-shared,
plant-wide energy assessment.
Plant assessments provide the opportunity to work
with BestPractices’ Allied Partners to develop case
studies that document the results of the assessments
and any efficiency upgrades. Such written reports
provide positive public relations with existing and
potential customers, and with the plant’s surrounding
community.
Service Providers. Organizations that provide equip-
ment, advice, or other services to manufacturers
benefit by becoming Allied Partners. BestPractices
provides Allied Partners with the technical support,
software, and materials to improve users’ knowledge
of energy-efficient motor, steam, compressed air,
and other industrial systems. In addition, Allied
Partners who provide these unbiased materials to
their clients are seen as credible resources for
industrial customers.
Allied Partners can gain additional access to the
media. For example, an Allied Partner can refer
customers who have completed energy efficiency
improvements to BestPractices. These projects may
be featured in Industrial Technologies case studies,
Energy Matters newsletter, and on the BestPractices
and Industrial Technologies Web sites.
Industry Trade or Technical Associations. Original
equipment manufacturers’ trade associations, end-
user industry associations, and utility consortia
also work with BestPractices as Allied Partners.
Associations often work with BestPractices to
create new efficiency guidelines, products,
materials, and services.
◆ Benefits of a Systems Approach
BestPractices encourages use of the “systems
approach” energy system design and analysis.
The systems approach seeks to increase the
efficiency of systems by shifting the focus from
individual components and functions to total

Figure 3-1. Motor System Diagram
system performance (see Figure 3-1). When
applying the systems approach, system design and
manufacturing best practices seek to optimize per-
formance in the entire process system, and then focus
on selecting components and control strategies that
best match this optimized system. The steps involved
in accomplishing a system optimization include:
■ Characterizing the process load requirements
■ Minimizing distribution losses
■ Matching the equipment to load requirements
■ Controlling the process load in the most optimal
manner, considering all cycles of the process load
■ Properly matching the system components to
each other as well as to the load.
Figure 3-2 shows that two-thirds of the potential
manufacturing motor system savings are “system”
related, demonstrating that management decisions
and technical actions that support a systems
approach at the corporate and plant level will be
the key to achieving large-scale energy efficiency
improvement in manufacturing motor systems.
Motor Systems Market Study. A study commissioned
by DOE has estimated that optimizing industrial
motor systems through the implementation of mature,
proven, cost-effective energy-savings techniques
can reduce industrial energy consumption by 75 to
122 billion kilowatt-hours per year, or up to $5.8
billion per year. These estimates include only the
energy savings and do not factor in other benefits
likely to result from optimization. Benefits include
improved control over production processes, reduced
maintenance, and improved environmental compli-
ance. This study is based on on-site surveys of 265
industrial facilities in the United States, in a statistically
based sampling of the manufacturing sector. The study,
titled United States Industrial Electric Motor Systems
Market Opportunities Assessment, can be downloaded
from the BestPractices Web site at www.oit.doe.gov/
bestpractices or obtained through the Industrial
Technologies Information Clearinghouse at (800)
862-2086.
Figure 3-2. Savings Potential
System
Optimization
65%
Energy-Efficient
Motors
15%
Motor
Management
20%
Motor/Drive Subsystem
Power Controls Motor Coupling Load Process
Process Mechanical and Electrical Feedback
The Electric Motor System
Mechanical Subsystem
Three-phase
Input Power

Table 3-1. Financial Impact of Motor Consumption and Savings for Selected Industries
Table 3-1 displays motor systems energy use and
potential savings per establishment in the ten
4-digit Standard Industrial Classification groups
with the highest annual motor energy consumption.
In all these industries, the annual cost of motor
system energy in a typical plant exceeds $1 million;
in steel mills, the energy cost is $6 million. Potential
savings at the typical plant are also large, ranging
from $90,000 per year in the industrial organic
chemicals sector to nearly $1 million per year in
petroleum refineries.
The right-hand column of Table 3-1 shows potential
energy savings as a percentage of operating margin.
These figures suggest the potential impact of motor
energy savings on the bottom line. The process
industries listed in Table 3-1 operate on thin margins:
the difference between revenues from sales and
variable costs, including labor, materials, and sell-
ing costs. In 1996, operating margins for the groups
listed below ranged from 10 to 24 percent and
clustered around 16 percent. Thus, even relatively
small increases in operating margin can have a
significant impact on profitability.
Educational and informational materials, including
additional copies of this sourcebook and further
information on all aspects of the BestPractices
Program are available by calling the Information
Clearinghouse at (800) 862-2086. Information is
also available at the BestPractices Web site at
www.oit.doe.gov/bestpractices.
Air Movement and Control
Association International, Inc.
(AMCA International)
◆ Introduction to AMCA International
AMCA International is a not-for-profit international
association of the world’s manufacturers of related
air system equipment. Such equipment primarily
includes fans, louvers, dampers, air curtains, air-
flow measurement stations, acoustic attenuators, and
other air system components for the industrial,
commercial, and residential markets. The association’s
mission is to promote the health and growth of
industries covered by its scope and the members
of the association consistent with the interests of
the public. It encourages the effective and efficient
use of air systems. AMCA International, with origins
dating back to 1917, has members in most
industrialized countries throughout the world.
Motor Energy Savings per Savings as Percent
Motor Systems Costs/Total Establishment per of Operating
Industry Groups Costs/Establishment Operating Costs Year Margin
Paper Mills 4.6 million 6.5% $659,000 5%
Petroleum Refining 5.6 million 1.4% $946,000 1%
Industrial Inorganic 1.6 million 10.4% $283,000 6%
Chemicals, nec.
Paperboard Mills 3.0 million 6.4% $492,000 5%
Blast Furnaces and 6.0 million 2.1% $358,000 2%
Steel Mills
Industrial Organic 1.3 million 1.0% $91,000 1%
Chemicals, nec.
Industrial Gases 1.1 million 21.7% $116,000 13%
Plastics Materials 1.5 million 1.5% $121,000 4%
and Resins
Cement, Hydraulic 2.2 million 9.6% $219,000 4%
Pulp Mills 1.7 million 6.7% $483,000 5%
Sources: Manufacturers Energy Consumption Survey 1994, Bureau of Economic Analysis 1997, Census of Manufacturers 1993,
and United States Industrial Electric Motor Systems Market Opportunities Assessment, U.S. Department of Energy, 1998.

In 1917, a group of centrifugal fan manufacturers
decided to exchange credit information and other
ideas, thus creating the National Association of Fan
Manufacturers (NAFM). The association grew
steadily during the next several decades and devel-
oped into a multi-service trade association with
heavy emphasis on engineering standards and
product performance testing. Over the years, the
association merged with other similar groups
including the Home Ventilating Institute (HVI),
an association of manufacturers of residential
air movement equipment. HVI joined AMCA
International as the HVI Division in 1985. AMCA
International, headquartered in Arlington Heights,
Illinois, continues to expand and enlarge its product
scope to meet the changing needs of industry.
AMCA International provides a variety of services
to its members and the air movement and control
industry, including its Certified Ratings Program,
Standards, and Testing Laboratories. The following
sections provide information on these services.
◆ AMCA International’s Certified
Ratings Program
AMCA International’s Certified Ratings Program
(CRP) was developed in response to the concerns
about product performance by buyers, specifiers,
and users of air movement and air control devices.
The CRP assures that a product line has been tested
and rated in conformance with AMCA International
or Industrial Standards Organization (ISO) test
standards and rating requirements. Only after a
product has been tested and the manufacturer’s
catalogued ratings have been submitted to and
approved by AMCA International staff can
performance seals be displayed in literature and on
equipment. Currently, AMCA International has the
world’s only international CRP for air system
components. Each licensed product line is subject
to continual check tests in AMCA International’s
laboratories. All licensed products are open to
challenge testing, which can be initiated by
competing manufacturers. Participation in the CRP
is voluntary and open to both AMCA International
nonmembers and members. AMCA International
maintains the Directory of Products Licensed to
Use the AMCA International Certified Ratings Seal
on its Web site at www.amca.org. The information
on certified products is updated on a daily basis.
◆ AMCA International Standards
AMCA International, backed by almost 80 years of
standards development, is the world’s leading
authority in the development of the science and art
of engineering related to air movement and air
control devices. AMCA International publishes and
distributes standards, references, and application
manuals for specifiers, engineers, and others with
an interest in air systems to use in the selection,
evaluation, and troubleshooting of air system
components. Many of AMCA International’s
standards are accepted as American National
Standards. Descriptions of AMCA International’s
publications are contained in AMCA International’s
Publication Catalogue, which is available free-of-
charge from the association, or can be viewed on
AMCA International’s Web site at www.amca.org.
AMCA International and its member companies
and laboratories are located in many industrialized
countries around the world. These organizations
are active on the technical committees of the ISO
and participate in the development of international
standards for industry.
◆ The AMCA International Test Laboratory
The AMCA International test laboratory is located
in Arlington Heights, Illinois, and accredited AMCA
International laboratories are located around the
world. Independent accredited AMCA International
laboratories, located in the United Kingdom and
Taiwan, function much like AMCA International’s
primary laboratory. Negotiations are underway to
approve other designated, independent accredited
AMCA International test laboratories around the world.
The AMCA International test laboratory is equipped to
test fans in accordance with the following standards:
■ ANSI/AMCA 210, Laboratory Method of Testing
Fans for Aerodynamic Performance Rating
■ AMCA 220, Test Methods for Air Curtain Units
Air Circulator Fans for Rating
Positive Pressure Ventilators
AMCA International also has a series of test standards
for sound testing of fans using various testing

methods, and a standard for the field testing of
industrial process/power generation fans (AMCA
Standard 803.) These standards, as well as application
guides and certified ratings programs, are described
in AMCA International’s Publications Catalogue.
AMCA International tests to international standards,
including those of the ISO, and participates in the
international development of standards for industry.
Test standards provide an important equipment
performance yardstick, while customer feedback
provides an application yardstick. AMCA
International research contributes to improved test
standards or evaluation of application conditions.
The AMCA International laboratory also provides a
reference standard for testing by other laboratories.
Many laboratories around the world compare their
product test data with the AMCA International
laboratory test data on identical products. An overall
improved fan system performance results from the
application of AMCA International standards.
For additional information on AMCA International’s
products and services, call (847) 394-0150, or visit
the AMCA International Web site at www.amca.org.
Directory of Contacts
The following organizations can provide more
information on improving the performance of fans
and fan systems.
The U.S. Department of Energy
Information Clearinghouse
P.O. Box 43171
Olympia, WA 98504-3171
Phone: (800) 862-2086
Fax: (360) 586-8303
www.oit.doe.gov/bestpractices
The Information Clearinghouse provides resources
and information on improving electric motor
systems, including fan systems.
Air Movement and Control Association International,
Inc. (AMCA International)
30 West University Drive
Arlington Heights, IL 60004-1893
Phone: (847) 394-0150
Fax: (847) 253-0088
www.amca.org
AMCA International is a not-for-profit international
association of the world’s manufacturers of related
air system equipment. Such equipment primarily
includes fans, louvers, dampers, air curtains, air-
flow measurement stations, acoustic attenuators,
and other air system components for the industrial,
commercial, and residential markets. The
association’s mission is to promote the health and
growth of industries covered by its scope and the
members of the association consistent with the
interests of the public.
American National Standards Institute (ANSI)
11 West 42nd Street
New York, NY 10036
Phone: (212) 642-4900
Fax: (212) 398-0023
web.ansi.org
ANSI is a professional society that develops and
maintains standards for a broad range of goods
and services. ANSI has approved several standards
on fan performance for testing purposes.
American Society of Heating, Refrigerating and Air
Conditioning Engineers (ASHRAE)
1791 Tullie Circle, NE
Atlanta, GA 30329
Phone: (404) 636-8400
Fax: (404) 321-5478
www.ashrae.org
ASHRAE is a professional society that promotes
the responsible development and use of heating,
ventilating, and air conditioning (HVAC) technologies.
Because fans have a significant impact on HVAC
system performance, ASHRAE has an interest in
fan design, selection, operation, and maintenance.
Consortium for Energy Efficiency, Inc. (CEE)
One State Street
Suite 1400
Boston, MA 02109-3507
Phone: (617) 589-3949
Fax: (617) 589-3948
www.cee1.org
CEE is a national, non-profit public benefits corpo-
ration that promotes the manufacture and purchase
of energy-efficient products and services. CEE’s
goal is to induce lasting structural and behavioral

changes in the marketplace, resulting in the
increased adoption of energy-efficient technologies.
CEE provides a forum for the exchange of information
and ideas. CEE members include utilities, statewide
and regional market transformation administrators,
environmental groups, research organizations, and
state energy offices. Also contributing to the
collaborative process are CEE partners, including
manufacturers, retailers, and government agencies.
Energy Center of Wisconsin (ECW)
595 Science Drive
Madison, WI 53711-1076
Phone: (608) 238-4601
Fax: (608) 238-8733
www.ecw.org
ECW finds ways to use energy more efficiently by
providing research, education, and energy
information. ECW works closely with government
organizations, businesses, research and develop-
ment organizations, advocacy groups, and
Wisconsin’s electric and gas utilities to promote
energy efficiency and demonstrate ideas that
benefit both energy producers and energy con-
sumers. ECW also conducts and sponsors a variety
of energy-efficiency research.
Iowa Energy Center
2521 Elwood Drive Suite 124
Ames, Iowa 50010-8229
Phone: (515)-294-8819
Fax: (515)-294-9912
www.energy.iastate.edu
The Center’s mission is to increase energy efficiency
in all areas of energy use. It conducts and sponsors
research on energy efficiency, conservation, and
alternative energy systems that are based on
renewable resources. The Center assists in assessing
technology related to energy efficiency and
alternative energy production systems. It also
supports educational and demonstration programs
that encourage implementation of energy-efficient
and alternative-energy production systems
New York State Energy Research and Development
Authority (NYSERDA)
Corporate Plaza West
286 Washington Avenue Extension
Albany, New York 12203-6399
Phone: (518) 862-1090
www.nyserda.org
NYSERDA is a public benefit corporation that
provides energy efficiency services, including those
directed at the low-income sector, research and
development, and environmental protection
activities. NYSERDA has successfully developed
and brought into use more than 125 innovative,
energy-efficient, and environmentally beneficial
products, processes, and services.
Sheet Metal and Air Conditioning Contractors
National Association
4201 Lafayette Center Drive
Chantilly, VA 20151-1209
Phone: (703) 803-2980
Fax: (703) 803-3732
www.smacna.org
Northeast Energy Efficiency Partnerships, Inc. (NEEP)
5 Militia Drive
Lexington, MA 02421
Phone: (781) 860-9177
Fax: (781) 860-9178
www.neep.org
NEEP is a non-profit regional organization with a
mission to increase energy efficiency in homes, build-
ings, and industry throughout the Northeast region
of the United States. NEEP’s general method is to
recognize and engage all concerned and capable
organizations in regional initiatives that promise
greater results than an assortment of subregional
(state or service territory) efforts could produce.
The Northwest Energy Efficiency Alliance
522 SW Fifth Ave., Suite 410
Portland, Oregon 97204
Phone: (800) 411-0834
Fax: (503) 827-8437
www.nwalliance.org
The Alliance seeks to bring about significant and
lasting changes in markets for energy-efficient tech-
nologies and practices, to improve the Pacific
Northwest region’s efficient use of energy, and
reduce costs to consumers and the electric system.
The Alliance has documented several case studies
that demonstrate how energy projects have
improved fan system performance.

Resources and Tools
A wide range of information is available on the
application and use of fans. This section of the
sourcebook will focus on resources and tools in
these formats:
■ Books
■ Brochures/Guides/Manuals
■ Software
■ Training Courses
■ Periodicals
■ Reports and Technical Papers
■ Videos and Slide Programs
■ Other Sources of Information.
Note: The descriptions accompanying the following
sources have generally been taken directly from
the publisher/author/developer. Inclusion of these
sources does not imply endorsement by DOE.
ASHRAE Handbook
Author/Publisher: American Society of Heating,
Refrigerating, and Air-Conditioning Engineers
ISBN: Series publication in which each volume
has a separate ISBN record.
Axial Flow Fans and Compressors: Aerodynamic
Design and Performance
Author: McKenzie, A.B.
Publisher: Ashgate, Aldershot; Brookfield, VT, 1997.
ISBN: 0291398502
Axial Flow Fans and Ducts
Author: Wallis, R. Allen.
Publisher: Krieger Publishing Company, NY, 1983.
ISBN: 0894646443
Centrifugal Pumps and Blowers
Author: Church, Austin.
Publisher: Kreiger Publishing Company,
Melbourne, FL, 1972.
ASIN: 0882750089
Compressors and Fans
Author: Cheremisinoff, Nicholas P.
Publisher: Prentice Hall, Englewood Cliffs, NJ, 1992.
ASIN: 013159740X
Fans, 2nd ed.
Author: Osborne, William C.
Publisher: Pergamon Press, Oxford, NY, 1977.
ASIN: 0080217265
Fans, Design and Operation of Centrifugal,
Axial-flow, and Cross-Flow Fans
Author: Eck, Bruno.
Publisher: Pergamon Press, Oxford, NY, 1973.
Translated by Ram S. Azad and David R. Scott.
ASIN: 0080158722
Fan Handbook: Selection, Application, and
Design
Author: Bleier, Frank P.
Publisher: McGraw Hill, New York, NY, 1997.
ISBN: 0070059330
A Guidebook to Electrical Energy Savings at
Lumber Dry Kilns through Fan Speed Reduction
Author: Caroll, Hatch & Associates.
Publisher: Bonneville Power Administration
Portland, OR.
Industrial Ventilation (23rd ed.)
Publisher: American Conference of Governmental
and Industrial Hygenists, 1998.
ISBN: 1882417224
Mine Ventilation and Air Conditioning
Author: Hartman, Howard L. (ed), et al.
Publisher: John Wiley & Sons, 1997.
ISBN: 0471116351
Moving Air Through Fans and Ducts (Tech-Set
Series)
Author: Gladstone, John.
Publisher: Engineers Press, 1992.
ISBN: 0930644174
Pumps/Compressors/Fans: Pocket Handbook
Author: Cheremisinoff, Nicholas P. and Paul N.
Cheremisinoff.
Publisher: Technomic Publishing, 1989.
ISBN: 0877626235
Books

The following publications and standards are
available from:
AMCA International
Arlington Heights, IL, 60004-1893
Phone (847) 394-0150
Fax (847) 253-0088
E-mail: amca@amca.org
Web site: www.amca.org
AMCA Publication 9.5—Why Buy an ‘Efficient’
Agricultural Fan?
AMCA Publication 99-86—Standards Handbook
AMCA Publication 302-73—Application of Sone
Ratings for Non-ducted Air Moving Devices
AMCA Publication 303-79—Application Sound
Power Level Ratings for Fans
AMCA Publication 410-96—Recommended Safety
Practices for Users and Installers of Industrial and
Commercial Fans
AMCA Publication 801-01—AMCA Industrial
Process/Power Generation Fans: Specifications
Guidelines
AMCA Publication 802-92—Industrial Process
Power Generation Fans: Establishing Performance
Using Laboratory Models
AMCA Standard 300-96—Reverberant Room
Method for Sound Testing of Fans
AMCA Standard 301-90—Method for Calculating
Fan Sound Ratings from Laboratory Test Data
AMCA Standard 803-96—Industrial
Process/Power Performance Fans: Site
Performance Test Standard
ANSI/AMCA Standard 204-96, Balance Quality
and Vibration Levels for Fans
ANSI/AMCA Standard 210-99—Laboratory
Methods of Testing Fans for Aerodynamic
Performance Rating
Methods of Testing Air Circulator Fans for Rating
Methods of Testing Positive Pressure Ventilators
ANSI/AMCA Standard 330-97—Laboratory Method
of Testing to Determine the Sound Power in a Duct
Fan Application Manual, Air Movement and Control
Association International, Inc., 1975. Note: This
manual includes four informative publications:
Publication 200-95—Air Systems,
Publication 201-90—Fans and Systems,
Publication 202-98—Troubleshooting, and
Publication 203-90—Field Performance
Measurement of Fan Systems
Other Brochures/Guides/Manuals
ASHRAE Standard 90.1-2001—Energy Standard
for Buildings Except Low-Rise Residential
Buildings, American Society of Heating,
Refrigerating, and Air-Conditioning Engineers, Inc.,
Atlanta, GA, 2001.
Displacement Compressors, Vacuum Pumps, and
Blowers, American Society of Mechanical Engineers,
[Performance Test codes; 9-1970], New York, 1970.
Energy Saving in the Design and Operation of
Fans, Institution of Mechanical Engineers,
Mechanical Engineering Publications, London, 1995.
HVAC Air Duct Leakage Test Manual, Sheet Metal
and Air Conditioning Contractors National
Association, Chantilly, VA, 1985.
Motor Repair Tech Brief Information, U.S.
Department of Energy, Office of Industrial
Technologies Clearinghouse, Washington, DC, 2000.
Process Fan and Compressor Selection,
(ImechE guides for the process industries)
Davidson, John and Otto von Bertele (eds.).,
Mechanical Engineering Publications, London, 1996.
The Selection and Use of Fans, Osborne, William
C. [Engineering design guides series], Design
Council, The British Institution and The Council of
Engineering Institutions by Oxford University
Press, 1979.
Brochures/Guides/Manuals

ASDMaster
Developer:
Electric Power Research Institute and
Bonneville Power Administration
This software package consists of six modules design-
ed to educate and assist users in the proper applica-
tion of adjustable speed drives (ASDs). ASDMaster
contains instruction tools that discuss the technology,
process effects, and power quality issues associated
with ASDs. It also analyzes energy consumption and
performance differences between ASDs and constant
speed alternatives. ASDMaster contains a database
module that refers the user to manufacturers of ASDs
that can meet the needs of the application.
Available from:
Industrial Technologies Information Clearinghouse
P.O. Box 43171
925 Plum Street
Phone: (800) 862-2086
Fax: (360) 586-8303
Email: motorline@energy.wsu.edu
Web site: www.oit.doe.gov/bestpractices
CFSWin
Developer:
Cincinnati Fan
The Cincinnati Fan Selector for Windows guide
allows the user to input fan requirements and
operating constraints. The program provides a list of
fans that satisfy the user requirements.
Available from:
Cincinnati Fan
7697 Snider Road
Mason, OH 45040-9135
Phone: (513) 573-0600
Fax: (513) 573-0640
Web site: www.cincinnatifan.com
C-Max Software: Fluid Flow Analysis
Developer:
UNICADE, Inc.
This software program was developed for industrial
and large commercial systems’ design, engineering,
energy efficiency program analysis, and life-cycle
cost evaluation. C-MAX is designed for consulting
engineers, design professionals, process plant engi-
neers, energy engineers, and electric utilities.
Available from:
UNICADE, Inc.
13219 NE 20th Street, Suite 211
Bellevue, WA 98005-2020
Phone: (425) 747-0353
Computer-Aided Product Selection (CAPS)
Developer:
ABC Industries
This program helps users make fan selection deci-
sions. The program facilitates the specification
process for the manufacturer’s fans, which are
designed for the mining and tunneling industries.
Available from:
ABC Industries, Inc.
301 Kings Highway
P.O. Box 77
Warsaw, IN 46581
Phone: (574) 267-5166
Fax: (574) 267-2045
Web site: www.abc-industries.net
Computer Aided Product Selection (CAPS)
Developer:
Greenheck Fan Corporation
CAPS is an electronic catalog and fan selection pro-
gram. The software helps users select a fan, and pro-
vides operating data such as fan performance curves.
Available from:
Greenheck Fan Corporation
P.O.Box 410
Schofield, WI 54476-0410
Phone: (715) 359-6171
Fax: (715) 355-2399
Web site: www.greenheck.com
Software

Fan Selector
Developer:
Twin Cities Fan Companies, Ltd.
The Fan Selector software is a Windows®-based
fan selection program, featuring selections from
over 190 product lines. The program provides per-
formance operating data, power requirements, and
sound data. Other features include 50 and 60 Hz
selection, density adjustments, performance cor-
rections for inlet and outlet appurtenances, and
automatically calculated wheel diameters to match
direct drive speeds.
Available from:
Twin City Fan Companies, Ltd.
5959 Trenton Lane
Minneapolis, MN 55442
Phone: (763) 551-7600
Fax: (763) 551-7601
Web site: www.twincityfan.com
Fansizer
Developer:
Penn Ventilation
Fansizer is a fan selection guide that allows the user
to input fan requirements and operating constraints.
The program provides a list of fans that satisfy the
user requirements.
Available from:
Penn Ventilation
4509 Springfield Street
Dayton, OH 45431
Phone: (937) 475-6500
Fax: (937) 254-9519
Web site: www.pennvent.com
FANtastic!®
Developer:
ACME Engineering and Manufacturing Corporation
FANtastic!® is a fan selection program with project
management capabilities that supports all ACME
fan lines with performance and sound ratings. It
offers the ability to plot performance curves to any
graphics screen and to a wide variety of printers.
If required, appurtenance derating factors for drive
losses, etc., are available.
Available from:
ACME Engineering and Manufacturing Corporation
P.O. Box 978
Muskogee, OK 74402
Phone: (918) 682-7791
Fax: (918) 682-0134
Web site: www.acmefan.com
Fan-to-Size Selection Program
Developer:
New York Blower Company
This software program helps users select the proper
fan. Using performance requirements, this program
can identify fans that meet the needs of the system.
The program can also provide operating data, such
as fan curves, noise levels, and power require-
ments.
Available from:
New York Blower Company
7660 Quincy Street
Willowbrook, IL 60521
Phone: (630) 794-5700
Fax: (630) 794-5776
Web site: www.nyb.com
MotorMaster+
Developer:
This software package assists users in calculating
motor operating costs and tracking the installation
and service characteristics for a plant’s motor
inventory. Additionally, MotorMaster+ contains a
database of motors from which the user can select
an appropriate model. The software allows consid-
eration of special service requirements, such as
high starting torque, severe duty, two-speed drives,
inverter duty, and medium-voltage (2,300- and
4,000-volt) power supplies. MotorMaster+ allows
users to track motor loads, maintenance histories,
and energy consumption.

Available from:
Industrial Technologies Information Clearinghouse
P.O. Box 43171
925 Plum Street
Phone: (800) 862-2086
Fax: (360) 586-8303
Email: motorline@energy.wsu.edu
Web site: www.oit.doe.gov/bestpractices
Optisizer: Fan Selection Software
Developer:
Stanley Fans
A software program developed to help users select
fans using standard or metric units. Fan selection
can be done by direct model, aided by competitors
cross-reference. Optisizer fan selection software is
designed for project managers.
Available from:
Stanley Fans
6393 Powers Avenue
Jacksonville, FL 32217
Phone: (904) 731-4711
Fax: (904) 737-8322
Email: e-mail@stanleyfans.com
Web site: www.stanleyfans.com
T-duct Software: Duct Design Computer Program
Developer:
NETSAL & Associates
This software program was developed to evaluate
the performance of a fan/duct system under various
conditions, adjust the fan operating point, and dis-
play actual airflow, mass flow rate, velocity, and
pressure profile at each duct section. T-Duct is
designed for consulting engineers, plant engineers,
and equipment manufacturers.
Available from:
NETSAL & Associates
Phone: (714) 531-2960
Fax: (714) 531-2960
Email: netsal@mail.apc.net
Web site: www.apc.net/netsal
AMCA International Technical Seminar
Description:
This 2-1/2-day course is offered biennially, usually
during the month of December. The seminar is
designed to provide information about the perform-
ance of fans, louvers, dampers, airflow measure-
ment stations, air curtains, acoustic attenuators, and
other related components that comprise an air sys-
tem. The seminar provides practical information
covering fundamental concepts of the latest technol-
ogy, which can save time and money in the recom-
mendation or selection of proper equipment, avoiding
installation errors and potential liability problems.
Participants gain an understanding of how the com-
ponents relate to each other and learn important fac-
tors in the selection and application of air system
components.
Available From:
AMCA International
Arlington Heights, IL 60004-1893
Phone: (847) 394-0150
Fax: (847) 253-0088
E-mail: amca@amca.org
Web site: www.amca.org
Duct Design Using T-Method Techniques
Description:
This 2-day seminar is devoted to teaching duct
design from fundamentals through computerized life-
cycle cost optimization and modeling. Attendees
will be provided with the method required to accu-
rately determine the most energy-efficient duct
pressure losses, optimized duct sizes, and air
velocities in a duct system. This course is intended
for project engineers, HVAC consulting engineers
and designers, and research and development spe-
cialists.
Available from:
NETSAL & Associates
Phone: (714) 531-2960
Fax: (714) 531-2960
E-mail: netsal@mail.apc.net
Web site: www.apc.net/netsal
Training Courses

Effective Fan Systems
Description:
This course—based on the Energy Center of
Wisconsin’s Optimizing the Performance of
Industrial Fan, Pump, and Blower Systems
course—focuses strictly on fan systems. A 2-day
course enables engineers to optimize the operation
of existing fans and to maximize the effectiveness
of new fans. A 1-day version is also available for
audiences that want to identify and qualify oppor-
tunities in new and existing systems but do not
need all of the engineering details.
Available from:
Productive Energy Solutions, LLC
2229 Eton Ridge
Madison, WI 53705
Phone: (608) 232-1861
Fax: (608) 232-1863
E-mail: pesco@chorus.net
Evaluation of Industrial Ventilation Systems
Description:
This 3-day course is offered once a year during the
month of August. Participants are provided with
training, information, hands-on experience, and
practical guidance in conducting inspections and
evaluating the performance of industrial ventilation
systems. This course is designed specifically for
engineers, industrial hygiene and safety profession-
als, and HVAC personnel.
Available from:
Centers for Education and Training
317 George Street, Plaza II, 2nd Floor
New Brunswick, NJ 08901-2008
Phone: (732) 235-9450
Fax: (732) 235-9460
E-mail: cet@eohsi.rutgers.edu
Web site: www.eohsi.rutgers.edu
Optimizing the Performance of Industrial Fan,
Pump, and Blower Systems
Description:
This 2-day fan and pump system optimization
course was developed by the Energy Center of
Wisconsin and DOE BestPractices. Students
explore fan optimization techniques, including
changing belt ratios, pony fans, and parallel fans.
Students examine the different system types to bet-
ter match the machine to the needs of the process.
Students also explore the proper application of fans
and pumps, applying ASDs in fan and pump sys-
tems, and minimizing system effect. Also available
is a 1-day course on identifying and prioritizing opti-
mization opportunities in new and existing systems.
Available from:
Energy Center of Wisconsin
595 Science Drive
Madison, WI 53705
Phone: (608) 238-4601
Fax: (608) 238-8733
Web site: www.ecw.org

ASHRAE Journal
American Society of Heating, Refrigeration, and
Air-Conditioning Engineers (ASHRAE), Atlanta, GA
Phone: (800) 527-4723
Web site: www.ashrae.org
Consulting-Specifying Engineer
Cahners Publishing Company, A Division of Reed
Elsevier Properties, Inc., Des Plaines, IL
Phone: (212) 519-7700
Web site: www.csemag.com
Electrical Construction and Maintenance
Primedia Business Magazines and Media,
Overland Park, KS
Phone: (800) 441-0294
Web site: www.primediabusiness.com
Heating/Piping/Air-Conditioning (HPAC)
Engineering
Penton Publishing, Cleveland, OH
Phone: (216) 696-7000 x9291
Web site: www.hpac.com
IEEE Control Systems Magazine
Institute of Electrical and Electronics Engineers
(IEEE), Control Systems Society (CSS),
Indianapolis, IN
Phone: (800) 272-6657
Web site: www.ieee.org
IEEE Industry Applications Magazine
Institute of Electrical and Electronics Engineers
(IEEE), Industry Applications Society (IAS),
Indianapolis, IN
Phone: (800) 272-6657
IEEE Power Engineering Magazine
Institute of Electrical and Electronics Engineers,
Power Engineering Society (PES), Los Angeles, CA
Phone: (800) 272-6657
Industrial Maintenance & Plant Operation (IMPO)
Phone: (212) 519-7700
Web site: www.impomag.com
Mechanical Engineering
American Society of Mechanical Engineers (ASME),
New York, NY.
Phone: (800) 843-2763
Web site: www.asme.org
Plant Engineering
Phone: (630) 320-7144
Web site: www.plantengineering.com
Plant Services
Putnam Publishing, Itasca, IL
Phone: (630) 467-1300
Web site: www.plantservices.com
Pollution Engineering Magazine
Pollution Engineering, Troy, MI
Phone: (248) 244-1737
Web site: www.pollutionengineering.com
Periodicals

Air Handling Equipment Energy Efficiency
Standards Program, Science Applications, Inc.,
California Energy Commission, publisher.
(Consultant report), Sacramento, CA, 1982.
CEC#: 400-80-75.
A Study of the Energy Savings Possible by
Automatic Control of Mechanical Draft Cooling
Tower Fans, (Conservation paper), Gordon
Associates, Washington, DC, U.S. Federal Energy
Administration, Office of Industrial Programs, 1975.
GPO Item #: 434-A-10.
“Discharge Diffuser Effect on Performance-Axial
Fans,” Galbraith, L. E., AMCA Paper 1228-82-A6.
Energy-Efficient Fan Component Detailed Design
Report, Halle, J.F., and C.J. Michael, Cleveland,
OH, NASA-Lewis Research Center, 1981.
GPO Item #: 30-II-14 (MF).
“Fan Performance Testing and the Effects of the
System,” Cory, W. T. W., AMCA Paper 1228-82-
A6.
Field Performance of Erosion-Resistance Materials
on Boiler-Induced Fan Blades, Karr, Orval F., J.B.
Brooks, and Ed Seay, Tennessee Valley Authority,
Kingston Fossil Plant, 1993. GPO Item #: 1082
(MF).
Impact of Using Auxiliary Fans on Coal Mine
Ventilation Efficiency and Cost, Wallace, Keith G.,
Jr., U.S. Dept. of the Interior, Bureau of Mines,
Washington, DC, 1990, GPO Item #: 0637-A (MF).
Installation Effects in Ducted Fan System,
Institution of Mechanical Engineers, Engineering
Sciences Division and Power Industries Division,
Westminster, London, 1984.
Installation Effects in Fan Systems, [Proceedings of
the Institution of Mechanical Engineers European
Conference], London, 1990.
Limiting Noise From Pumps, Fans, and
Compressors, Institution of Mechanical Engineers,
Fluid Machinery Group, (Conference), ImechE
conference publications; 1977-10, London, 1977.
Market Baseline Evaluation Report: Fan Speed
Reduction in Pneumatic Conveying Systems in the
Secondary Wood Products Industry, SBW
Consulting, Northwest Energy Efficiency Alliance,
November, 1999.
Papers Presented at the International Conference
on Fan Design & Applications, International
Conference on Fan Design and Applications.
sponsored by BIIRA Fluid Engineering England,
[H.S. Stephens and Mrs. G.B. Warren, eds.],
Bedford, UK, 1982.
Power Station Pumps and Fans: International
Conference, Institution of Mechanical Engineers,
Power Industries Division, Proceedings of the
Institution of Mechanical Engineers,
Co-sponsored by EPRI, London, 1992.
Authority, Kingston Fossil Plant, 1993.
GPO Item #: 1082 (MF).
System Effect Factors for Axial Flow Fans, Zaleski,
R. H., AMCA Paper 2011-88, AMCA Engineering
Conference, 1988.
System Effects on Centrifugal Fan Performance,
Traver, D. G., ASHRAE Symposium Bulletin,
Fan Application Testing and Selection, 1971.
Reports/Technical Papers
SP2: Fans and Air Systems, Air Movement and
Control Association International, Inc. (Slide pro-
gram). Arlington Heights, IL.
V3: System Effect, Optimum System Performance,
Air Movement and Control Association
International, Inc. (Video). Arlington Heights, IL.
Videos/Slide Programs

This appendix is a collection of terms used in
fans and fan systems. It is based primarily on
Engineering Letter G, written by The New York
Blower Company, and is used here with permission.
acceleration loss—the energy required to induce
air to move at the entry to a system
acfm—actual cubic feet per minute; the quantity
or volume of a gas flowing at any point in a sys-
tem. Fans are rated and selected on the basis of
ACFM, as a fan handles the same volume of air
regardless of density.
air conditioning—treating air to meet the require-
ments of a conditioned space by controlling its
temperature, humidity, cleanliness, and distribu-
tion.
air curtain—mechanical air-moving device
designed to limit the influx of unwanted air at a
building opening
air handling unit—factory-made encased assembly
consisting of a fan or fans and other equipment to
circulate, clean, heat, cool, humidify, dehumidify,
or mix air
ambient—immediate surroundings or vicinity
AMCA—Air Movement and Control Association
International, Inc.
anemometer—a device that reads air velocity, such
as a wind vane. In fan applications, it is
usually a spinning-vane-type instrument used to
read low velocities at registers or grills.
anneal—the process of relieving stress and brittle-
ness in metals by controlled heating and cooling
ANSI—American National Standards Institute
API—American Petroleum Institute
ARI—Air Conditioning and Refrigeration Institute
ASHRAE—American Society of Heating,
Refrigerating, and Air Conditioning Engineers
ASME—American Society of Mechanical Engineers
aspect ratio—the ratio of width to length
ASTM—American Society for Testing and Materials
atmospheric pressure—one atmosphere is
approximately 14.7 psi, 408” water gauge at sea
level. Airflow is the result of a difference in pressure
(above or below atmospheric) between two points.
attenuation—absorption of sound pressure.
Attenuation reduces the amplitude of a sound wave
while leaving the frequency unchanged.
axial fan—fan where the airflow through the
impeller is predominantly parallel to the axis of
rotation. The impeller is contained in a cylindrical
housing.
axial flow—in-line air movement parallel to the
fan or motor shaft
backdraft damper—damper used in a system to
relieve air pressure in one direction and to prevent
airflow in the opposite direction
backward-inclined fan—a group of centrifugal fans
with blades that angle back from the direction of
fan rotation. These fans can have curved and air-
foil blade shapes. Airfoil blades are among the
most efficient fan types.
balancing—the process of adding (or removing)
weight on a rotor in order to move the center of
gravity toward the axis of rotation
barometric pressure—a measurement of the
pressure of the atmosphere; standard atmospheric
pressure is 29.92” Hg at sea level
Appendix A: Fan System Terminology

bearing losses—power losses resulting from friction
in the main bearings
Bernoulli’s Theorem—the principle that the total
energy per unit of mass in the streamline flow of a
moving fluid is constant, being the sum of the
potential energy, the kinetic energy, and the energy
because of pressure. In terms of air movement, the
theorem states that static pressure plus velocity
pressure as measured at a point upstream in the
direction of airflow is equal to the static pressure
plus velocity pressure as measured at a point
downstream in the direction of airflow plus the
friction and dynamic losses between the points.
best efficiency point (BEP)—the operating condition
at which a fan transfers energy to an airstream most
efficiently. In general, this is a point on a fan curve
to the right of peak pressure.
blade liners—pieces of material added over the
impeller blades to reduce abrasion of the blades
blade-pass frequency—the tone generated by the
blades passing a fixed object
blast area—the fan outlet area less the projected
area of the cut-off
brake horsepower (bhp)—a measure of the rate of
energy expended. One bhp is equivalent to mechan-
ical energy consumed at a rate of 33,000-ft. lbs.
per minute.
breakdown torque—maximum torque a motor will
produce without a sudden decrease in speed. Often
referred to as pullout torque or maximum torque.
Btu—British thermal unit; heat required to raise the
temperature of 1 pound of water by 1°F
capture velocity—air velocity necessary to over-
come opposing air currents or natural flow and
cause contaminated air, fumes, or material to flow
in a desired direction
Celsius—a thermometric scale in which water
boils at 100° and freezes at 0°
centrifugal fan—a fan design in which air is
discharged perpendicular to the impeller’s
rotational axis
cfm—cubic feet per minute; the volume of flow for
a given fan or system
coatings—specialty coverings, typically referred to
as paints, with varying degrees of resistance to
atmospheric or chemical corrosion
coefficient of conductivity—the rate of heat transfer
through a material, expressed in Btu, transmitted
per hour through one square foot of surface per
degree difference in temperature across the material.
compressibility—a factor used by fan manufacturers
to correct performance ratings in higher pressure
ranges to account for the fact that air is a
compressible gas
compression—a phenomenon related to positive
pressure. When air is forced into a system it is
compressed and becomes more dense. Depending on
the volume or weight of air required downstream
in the positive-pressure portion of the system, the
volume of air at the inlet of a fan may have to be
adjusted by the ratio of absolute pressure at the
entrance of the fan versus the design requirements
in the system.
conveying velocity—the air velocity required in a
duct system to maintain entrainment of a specific
material
corrosion—the deterioration of a material by
chemical or electrochemical reaction resulting
from exposure to weathering, moisture, chemical,
or other agents in the environment in which it is
placed
curve, fan performance—a graphic representation
of static or total pressure and fan bhp requirements
over an airflow volume range
curve, system—a graphic representation of the
pressure versus flow characteristics of a given system
damper—an accessory to be installed at the fan
inlet or outlet for air-volume modulation
density—the measure of unit mass equal to its
weight divided by its volume (lbs./ft.3); standard air
is 0.075 lbs./ft.3

dew point—the temperature at which condensation
begins to form as air is cooled
dust—air suspension of particles [aerosol] of any
solid material, usually with a particle size smaller
than 100 micrometers
dust collector—an air-cleaning device used to
remove heavy-particulate loadings from exhaust
systems prior to discharge
DWDI—double-width, double-inlet fans
dynamic balance—the mechanical balancing of a
rotating part or assembly in motion
efficiency, mechanical total—the ratio of fan out-
put to the power applied to the fan; can be helpful
in selecting fan size, type, or manufacturer for the
same application
elevation—the distance of the subject site above or
below sea level
entry loss—the loss in pressure caused by air
flowing into a system; normally expressed in
fractions of velocity pressure
equivalent duct diameter—for rectangular duct
with sides a and b is:
evase—a diffuser at the fan outlet that gradually
increases in area to decrease velocity and to
convert kinetic energy to static pressure at the fan
outlet and inlet
Fahrenheit—a thermometric scale in which water
boils at 212°F and freezes at 32°F
fan—a power-driven machine that moves a
continuous volume of air by converting rotational
mechanical energy to an increase in the total
pressure of the moving air
fan capacity—performance requirement for which
a fan is selected to meet specific system calculations
given in terms of ACFM at the fan inlet
fan class—operating limits at which a fan must be
physically capable of operating safely
fan laws—theoretical constant relationships
between cfm, rpm, static pressure (sp), and bhp for
a given fan used in a given fixed system:
cfm ~ rpm
sp ~ (rpm)2
bhp ~ (rpm)3
foot-pound (ft.-lb.)—torque rating or requirement;
equivalent to the force required to move a
1-pound weight 1 foot in distance, equal to
12 in.-lb.
forced draft—how air is provided in a process,
such as a combustion process; when air is blown
or forced into a process, it is known as a “forced
draft” system. Also see Induced Draft.
forward-curved blade fan—a fan type with blades
that angle toward the direction of rotation. This fan
type generates relatively high pressure at low
operating speeds and is used frequently in residential
furnace applications
fpm—feet per minute; commonly defines air veloc-
ity (to determine velocity pressure or suitability for
material conveying), shaft/bearing speeds (used to
determine lubrication requirements), and impeller
tip speeds
frame size—a set of physical dimensions of motors
as established by National Electrical Manufacturers
Association (NEMA) for interchangeability between
manufacturers. Dimensions include shaft diameter,
shaft height, and motor-mounting footprint.
frequency—any cyclic event, whether vibration,
alternating current, or rotational speed. Usually
expressed in cycles per second (cps) or just “cycles.”
friction loss—resistance to airflow through any
duct or fitting, given in terms of static pressure
FRP—abbreviation for fiberglass-reinforced-plastic
full-load speed—the speed at which the rated
horsepower is developed. This speed is less than
synchronous speed and varies with motor type and
manufacturer.
4ab
Deff =
√ π

full-load torque—the torque required to produce
the rated horsepower at full-load speed
fumes—airborne particles, usually less than
1 micrometer in size, formed by condensation of
vapors, sublimation, distillation, or chemical reaction
gauge (gage)—metal manufacturers’ standard
measure of thickness for sheet stock
gauge pressure—the pressure differential between
atmospheric and that measured in the system
heat exchanger—a device, such as a coil or
radiator, which is used to transfer heat between
two physically separated fluids
HEPA filter—high-efficiency particulate air filters,
commonly called absolute filters
hertz—frequency measured in cycles per second
Hg—symbol for mercury. Pressure is often measured
in inches of mercury (1 inch Hg = 13.64 inches
wg).
horsepower (hp)—(as applied to motors) an index
of the amount of work the machine can perform in
a period of time. One hp equals 33,000-ft. lbs. of
work per minute, also equal to 0.746 kilowatts.
Horsepower can be calculated by:
housing—the casing or shroud of a centrifugal fan
HVAC—heating, ventilating, and air conditioning
impeller—another term for fan “wheel.” The
rotating portion of the fan designed to increase the
energy level of the gas stream.
impeller diameter—the maximum diameter
measured over the impeller blades
impingement—striking or impacting, such as
material impingement on a fan impeller
inch of water—unit of pressure equal to the
pressure exerted by a column of water 1 inch high
at a standard density (1 inch of water = 0.036 psig)
inch-pound (in.-lb.)—torque equal to one-twelfth
foot-pound
inclined manometer—a metering device used to
obtain pressure measurements
induced draft—how air is provided in a process,
such as a combustion process, where air is drawn
or pulled through a process. Also see forced draft.
induction—the production of an electric current in
a conductor in a changing magnetic field
inertia—tendency of an object to remain in the
state it is in. Also see WR2.
inlet-vane damper—round multiblade damper
mounted to the inlet of a fan to vary the airflow
instability—the point of operation at which a fan or
system will “hunt” or pulse; common in forward-
curved fans and some axial fan types where the
point of operation is left of the peak of the static-
pressure curve
kilowatt—measure of power equal to 1.34 horse-
power
L-10 bearing life—the theoretical number of hours
after which 90 percent of the bearings subjected to
a given set of conditions will still be in operation
laminar flow—gas or fluid in parallel layers with
some sliding motion between the layers, characteristic
of airstreams with Reynolds numbers less than 2,000
load factor—ratio of the average capacity to the
rated full capacity, determined by the following
relationship:
louver—a device composed of multiple blades
which, when mounted in an opening, permits the
flow of air but inhibits the entrance of undesirable
elements
Torque x RPM
horsepower =
5,250
Load ∑ (Actual Load x Number of operating hours at this load)
Factor
=
Rated Full Load x Number of hours in the period

make-up air—a ventilating term which refers to the
replacement of air lost because of exhaust air
requirements
manometer—instrument for measuring pressure;
u-shaped, and partially filled with liquid, either
water, light oil, or mercury
maximum continuous rating—the point at which
the fan is expected to operate
natural frequency—the frequency at which a com-
ponent or system resonates
NEMA—the National Electrical Manufacturers
Association; the trade association establishing
standards of dimensions, ratings, enclosures,
insulation, and other design criteria for electric
motors and other devices
noise criteria—a way for a designer to specify the
maximum permissible sound-power level in each
of the eight-octave bands. Noise criteria curves give
maximum permissible intensity per octave-band in
a graphical form.
opposed-blade damper—a type of damper where
adjacent blades rotate in the opposite direction
parallel-blade damper—a type of damper where
the blades rotate in the same direction
parallel fans—two or more fans that draw air from a
common source and exhaust into a common duct
or plenum. A parallel fan arrangement is generally
used to meet volume requirements beyond that of
single fans. Two identical fans in parallel will
effectively deliver twice the rated flow of any one
fan at the same static pressure.
pitch diameter—the mean diameter or point at
which V-belts ride within a sheave. This dimension
is necessary for accurate drive calculations.
pitot tube—a metering device consisting of a
double-walled tube with a short right-angle bend; the
periphery of the tube has several holes through which
static pressure is measured; the bent end of the tube
has a hole through which total pressure is measured
when pointed upstream in a moving gas stream
plenum—a chamber or enclosure within an
air-handling system in which two or more branches
converge or where system components such as
fans, coils, filters, or dampers are located
poles—the number of magnetic poles established
inside an electric motor by the placement and
connection of the windings
propeller fan—an axial fan type that is compact,
inexpensive, but relatively inefficient
psia—pounds per square inch absolute, represents
total pressure above a perfect vacuum
psig—pounds per square inch measured in gauge
pressure, represents the difference between psia
and atmospheric pressure
radial blade—fan impeller design with blades posi-
tioned in straight radial direction from the hub
radial-tip fan—a fan type with short blades and
large clearances between the blades and the
impeller hub
rarefication—a phenomenon related to negative
pressure. When air is drawn through resistance
into a fan inlet, the air is stretched out, or rarefied,
and becomes less dense than at the entry to the
system. While negligible at low pressures and
volumes, high-pressure fan selection must be
based on rarefied inlet density.
relative humidity—the ratio of existing water vapor
to that of saturated air at the same dry-bulb tempera-
ture
Reynolds number—a mathematical factor used to
express the relation between velocity, viscosity,
density, and dimensions in a system of flow; used
to define fan proportionality
rotor—the rotating part of most alternating current
motors
rpm—revolutions per minute
radial tip—fan impeller design with shallow blades
in which the trailing edge points radially from the
axis of rotation

saturated air—air containing the maximum amount
of water vapor for a given temperature and pressure
scfm—standard cubic feet per minute; a volume of air
at 0.075 lbs./ft.3 density; used as an equivalent weight
scroll—the general shape of a centrifugal fan hous-
ing; the formed piece to which housing sides are
welded
sensible heat—any portion of heat which affects a
change in a substance’s temperature but does not
alter that substance’s state
series fans—a combination of fans connected so
that the outlet of one fan exhausts into the inlet of
another. Fans connected in this manner are capable
of higher pressures than a single fan and are used to
meet greater pressure requirements than single fans.
service factor—the number by which the horse-
power rating is multiplied to determine the
maximum safe load that a motor may be expected
to carry continuously
shaft seal—a device to limit gas leakage between
the shaft and fan housing
slip—the percentage difference between
synchronous speed and actual speed
sound—produced by the vibration of matter. The
vibration causes sound waves to spread through
the surrounding medium.
surge limit—that point near the peak of the
pressure curve that corresponds to the minimum
flow at which the fan medium can be operated
without instability
sound-power level—acoustic power radiating from
a sound source; expressed in watts or in decibels
sound-pressure level—the acoustic pressure at a
point in space where the microphone or listener’s
ear is situated; expressed in units of pressure or in
decibels
specific gravity—the ratio of the weight or mass of
a given volume of any substance to that of an
equal volume of some other substance taken as a
standard. The ratio of the density of any gas to the
density of dry air at the same temperature and
pressure is the specific gravity of the gas.
specific heat—the ratio of the quantity of heat
required to raise the temperature of a certain
volume by one degree to that required to raise an
equal volume of water by one degree
squirrel-cage winding—a permanently short-
circuited winding, usually uninsulated and chiefly
used in induction motors, with its conductors
uniformly distributed around the periphery of the
machine and joined by continuous end rings
standard air density—0.075 lbs./ft.3, corresponds
approximately to dry air at 70°F and 29.92 in. Hg
stator—the stationary parts of a magnetic circuit
with operating speeds associated windings
synchronous speed—rated motor speed expressed
in rpm:
system curve—graphic presentation of the
pressure versus volume flow-rate characteristics of
a particular system
system effect—the difference between the actual
flow-pressure characteristics of a fan or a fan system
component and the flow-pressure characteristics
determined in laboratory tests to obtain performance
ratings
tachometer—an instrument which measures the
speed of rotation; usually in rpm
tensile strength—the maximum stress a material
can withstand before it breaks; expressed in
pounds per square inch
tip speed—fan impeller velocity at a point
corresponding to the outside diameter of the
impeller blades; normally expressed in feet per
minute (circumference times rpm)
torque—a force that produces rotation; commonly
measured in ft.-lbs. or in.-lbs.
120 x Frequency
Synchronous speed =
Number of poles

tubeaxial fan—axial fan without guide vanes
tubular centrifugal fan—fan with a centrifugal
impeller within a cylindrical housing that discharges
the gas in an axial direction.
turbulent flow—airflow in which true velocities at
a given point vary erratically in speed and direction
uniform flow—airflow in which velocities between
any two given points remain fairly constant
vaneaxial fan—axial fan with either inlet or
discharge guide vanes or both
ventilation—supplying and removing air by natural
or mechanical means to and from any space
vibration—alternating mechanical motion of an
elastic system, components of which are amplitude,
frequency, and phase
viscosity—the characteristic of all fluids to resist
flow
watt—a unit of power. In electrical terms, the
product of voltage and amperage; 746 watts are
equal to 1 horsepower
wg—water gage. Also see “inch of water.”
WR2—the unit designation of fan-impeller
rotational inertia in lb.-ft.2, also known as WK2

The fan marketplace connects manufacturers,
manufacturer representatives, engineering/specifying
companies, and mechanical contractors to a wide
range of fan end users. Fans are used in residential,
commercial, agricultural, and industrial fluid system
applications, where customer sophistication varies
widely. Consequently, fans are sold through several
different market channels. Customer knowledge,
system application, and fan cost are among the
principal factors that affect the structure of these
market channels. Industrial applications represent
the largest fan-market segment in terms of energy
consumption and are the primary focus in this
sourcebook.
◆ Market Size and Energy Consumption
In 1997, U.S. fan and blower manufacturers
recorded almost $2 billion in sales to industrial,
commercial, and residential customers. Most of the
energy improvement opportunities for fan systems
are found in the industrial sector. The installed
base of fans in the industrial sector consumes
about 79 billion kilowatt-hours annually, repre-
senting about 11 percent of all motor-driven indus-
trial electricity consumption in the United States.
Although the market segment of fans below 5
horsepower (hp) accounts for the largest number of
units sold, the segment of fans above 1,000 hp
accounts for the highest energy consumption.
◆ Market Distribution Channels
The fan marketplace is relatively complex, because
of the wide range of applications (see Figure B-1).
Fan manufacturers sell fans through two primary
channels: original equipment manufacturers (OEMs)
and manufacturer representatives. The key points
Appendix B: The Fan System Marketplace
Figure B-1. Industrial Fan Marketplace
Original
Equipment
Manufacturer
Fan Users
• Power
• Mining
• Chemical
• Pulp & Paper
• Petroleum
• Other Process
Industries
Fan
Manufacturer
Fan Manufacturer
Representative
Variable Frequency Drive
Manufacturer
Motor
Manufacturer
Mechanical
Contractor
Market influences, AMCA, ARI, Trade Associations, Government, Utilities

of influence for promoting market transformation
in the process fan systems market are:
■ Fan manufacturers and their internal sales staffs
■ Manufacturers representatives
■ Specifying engineers and mechanical
contractors
■ Fan users
■ Standards and trade associations
■ Engineering societies.
Fan Manufacturers. The U.S. fan market is relatively
distributed. Fan manufacturers include large
companies that produce a wide range of fan types
and comparatively small companies that specialize
in a few fan designs.
Although fan manufacturers generally consider fans
to be commodity items, they cite technical features,
such as operating efficiency and durability, as
competitive advantages. Some manufacturers use
engineering support and order fulfillment time as
selling points to swing purchase decisions in their
favor.
Manufacturers do not typically provide complete
system design services to fan customers, although
a few manufacturers offer engineering services to
assist in fan selection. Most fan sales and service
support is provided by manufacturer representatives.
Fan manufacturers also sell fans to OEMs for use
as part of packaged products, such as unitary air
conditioning units.
Another channel for fan sales is directly to end users
who need replacement fans. Fans in corrosive
environments often degrade and require replace-
ment before the end of the system’s service life. In
these cases, end users may request an entire fan
assembly or individual components, such as fan
wheels.
Manufacturer Representatives. Manufacturer
representatives are the primary links between the
manufacturer and the mechanical contractors.
Manufacturer representatives do not take possession
of the fans and are not exposed to the risk of sales.
Manufacturer representatives place orders for sales,
and the manufacturer ships the unit directly to the
fan customer.
Specifying Engineers and Mechanical Contractors.
Contractor and engineering firms often handle
turnkey production facility design, including system
design, fan sizing, and selection. New fan systems
are typically installed by mechanical contractors.
Consulting engineers provide design services and
help specify equipment for new facilities, as well
as major retrofits and system renovations.
The role of specifying engineers is to design
systems and select fans that meet the system’s
needs. These engineers must ensure the system
meets performance criteria; however, once the
system is installed and operating, the specifying
engineer’s task is complete. Because operating and
maintenance costs are future costs, not applied to
the capital budget, there is a tendency to focus on
initial system performance. This practice often
results in equipment that is oversized. The
constraint against sourcing oversized equipment is
the higher cost associated with larger equipment
rather than the need to keep life-cycle costs down.
Fan Users. Most fan users rely on mechanical
contractors/fan manufacturer representatives for fan
procurement. However, some large, sophisticated
fan users may use an in-house engineering staff to
design specialized systems and to source system
equipment, such as fans, motors, and control
systems. Evaluation criteria for fan selection
include initial cost, performance, and reliability.
The balance among these criteria changes according
to the sophistication level of the fan user, the needs
of the application, and resource constraints.
In many applications, fan systems are conservatively
designed, which results in the selection of over-
sized fans. A common perception is that the costs
of oversizing fans are small relative to the cost of
insufficient fan output. However, this practice
overlooks the life-cycle cost components of energy
use, maintenance requirements, and risk of failure,
all of which are increased by operating a fan that
is improperly sized for its system.
Although some fan users are sufficiently
knowledgeable about fan system operation to
know the problems associated with poor system
design practices, many do not recognize the
penalties of inefficient fan operation. In addition to

increasing energy consumption, oversizing a fan
sacrifices—rather than improves—long-term
reliability. Fan manufacturers, manufacturer
representatives, specifying engineers, and
mechanical contractors are stakeholders in initial
fan performance. However, the fan user alone pays
for the long-term operating and maintenance costs.
Standards and Trade Associations. Trade associations,
government entities, and electric utilities also play
vital roles in the process fan market. Two trade
associations are key players in the fan industry:
• The Air Movement and Control Association
International, Inc. (AMCA) is a not-for-profit
international association of the world’s manufac-
turers of related air system equipment—primarily,
but not limited to fans, louvers, dampers, air
curtains, airflow measurement systems, acoustic
attenuators, and other air system components—
for the industrial, commercial, and residential
markets. The association’s mission is to promote
the health and growth of industries covered by
its scope and the members of the association
consistent with the interests of the public.
AMCA International developed a Certified
Ratings Program in response to the concerns
over product performance on the part of buyers,
specifiers, and users of air movement and
control devices. Currently, AMCA International
has the world’s only existing international
certified ratings program for air system compo
nents. All licensed products are open to
challenge testing, which can be initiated by
competing manufacturers. Participation in the
Certified Ratings Programs is voluntary and
open to AMCA International nonmembers as
well as members.
AMCA International publishes and distributes
standards, references, and application manuals
for specifiers, engineers, and others with an
interest in air systems, for use in the selection,
evaluation and troubleshooting of air system
components. Many of AMCA International’s
standards are accepted as American National
Standards. AMCA International is active on the
technical committees of the International
Standards Organization (ISO) and participates
in the development of international standards
for the industry.
• American National Standards Institute (ANSI)
is a professional society whose goal is the
review and approval of standards for a broad
range of goods and services. This voluntary,
private-sector organization is made up of
manufacturers and industry professionals. ANSI
is the sole U.S. representative to the ISO and the
International Electrotechnical Commission (IEC).
The purpose of standards organizations is to
promote uniformity in the nonproprietary aspects
of products. This uniformity provides a valuable
interchangeability among the products of different
manufacturers; for example, a burned-out light
bulb may be replaced with a light bulb from any
manufacturer. This interchangeability allows
plants to maintain standard parts inventories
rather than keep special replacement items for
each piece of equipment.
With respect to fans, ANSI has approved several
standards on fan performance for testing purposes.
Most of these standards are relatively general
and do not require specific performance criteria.
To contact ANSI, see the Directory of Contacts
on page 65.
Engineering Societies. Engineering societies can be
useful in resolving fan system problems by referring
to resources or publications that describe how other
fan users have resolved similar problems. Two such
societies are:
• The American Society of Heating, Refrigerating,
and Air-Conditioning Engineers (ASHRAE)
is an international organization with the sole
purpose of advancing the arts and sciences of
heating, ventilation, air conditioning, and
refrigeration (HVAC&R) for the public’s benefit
through research, standards writing, continuing
education, and publications.
Through its membership, ASHRAE writes
standards that set uniform methods of testing
and rating equipment and establish accepted
practices for the HVAC&R industry worldwide,
such as the design of energy-efficient buildings.
The Society’s research program investigates

numerous issues, such as identifying new
refrigerants that are environmentally safe.
ASHRAE organizes broad-based technical
programs for presentation at its semi-annual
meetings and co-sponsors the International Air-
Conditioning, Heating, and Refrigerating
Exposition, the largest HVAC&R trade show in
North America.
• The Society of Tribologists and Lubrication
Engineers (STLE) focuses on issues of wear and
machine reliability, which translates to an interest
in predicting and avoiding failures in bearings
and mechanical seals. Fan users who experience
bearing or seal problems may benefit from the
STLE’s knowledge of lubrication, material
selection, and predictive analysis.

Improving fan system performance 1989-doe-92pp

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water and space heating
Weatherization & Intergovernmental Program
Acelerating the use of today’s best energy-efficient and renewable
technologies in homes, communities, and businesses
Wind & Hydropower Technologies Program
Harnessing America’s abundant natural resources for clean power
generation
To learn more, visit www.eere.energy.gov
To order additional copies of
this sourcebook, please call:
Industrial Technologies
Information Clearinghouse
(800) 862-2086
Energy Efficiency and Renewable Energy
Washington, D.C. 20585
DOE/GO-102003-1294
April 2003

Improving fan system performance 1989-doe-92pp

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