LECTURE 6 ZONING IN HVAC.ppt

SERVICES VI ( AR-310B)
LECTURE 6
ZONING AND AIR DISTRIBUTION
SYSTEMS

HOW DOES A ZONING SYSTEM WORKS IN HVAC
A zoning system for an HVAC system is a way to control the temperature
for each area, or “zone” in a home, rather than have to heat or cool the whole
house to the same temperature.
With a zoning system, we can set temperatures differently for either
individual rooms or sections of our home.

Once that thermostat calls for heating or cooling there is virtually no way
to control the temperature in each room of the house except by manually
closing off the outlets in eachroom.
This manual method is time-consuming and can cause harm to the
HVAC unit, as closing off too many outlets can reduce the airflow. This
could shortenthelife of the furnace, air conditioner or heat pump.

Zoning solves this problem.
Zoning allows us to save energy (and therefore money) by not heating or cooling
roomswhen theydon’t need it.
A zoning system is a professionally installed control system consisting of a damper
and thermostat for each room or zone of the house. This control system is wired into a
central control panel that sequences each thermostat’s call with the zone dampers in the
ducts andthe HVACsystem.

HOW DOES A ZONING WORK IN HVAC?
Zoning provides the ability to only condition those rooms that need
heating or cooling and does not allow conditioned air into those zones not
requiring it.
Zoning does this through a series of components, the first being motorized
dampers that openand closebased on the demands of the zone thermostats.
These dampers are inserted into the ducts or can be installed at the air
outlet for each roomor zone.
Multiple dampers can be controlled together for a single zone if multiple
ducts serve a singleroomor zone. We will discuss these later.

As each zone is divided, each zone uses a thermostat to control the
heating, cooling and fan operationfor its individual zone.
The zone thermostats and dampers are wired into a central control
panel.
The panel then also connects to the thermostat connections on the HVAC
Unit. Instead of using one central thermostat, the control panel allows the
unit to be controlledby multiple thermostats.

As each thermostat calls for heating or cooling, the panel takes the first call
fromany zone.
If it’s heating, for example, it will keep open the damper to the calling zone,
close the dampers to satisfied zones not calling for heating, activate the furnace
or heat pump and beginsupplying air only to that zone.
If during this call other zones call for heating, those zone dampers would
openand heatedair wouldbe supplied to those zones as well.
Once all heating calls are satisfied the panel will shut off the furnace or heat
pump.

ROOM AIR DISTRIBUTION SYSTEMS
HVAC airflow in spaces generally can be classified by two different
types: mixing (or dilution)and displacement.
Mixing Systems Of Air
Mixing systems generally supply air such that the supply air mixes with
the room air so that the mixed air is at the room design temperature and
humidity.
The high velocity supply air stream causes turbulence causing the room air to
mix withthe supplyair.

FANS IN HVAC
Fans push or pull air around the system. The simplest air distribution
systems use constant fan speed and constant-size damper openings.
However, Variable Air Volume ("VAV") systems change fan speed on the
fly, saving up to 10 - 20% of HVAC energy use.

DAMPERS IN HVAC
HVAC rely on dampers to help control indoor temperatures.
 They can also be shut in unused rooms to save energy costs or opened
wide to allow more air flow into one area that needs additional heating or
cooling.
In addition to offering different types according to function, dampers also
feature different styles, different leak ranges and how the damper is
controlled.
Picking the right HVAC damper initially requires narrowing down the
different typesaccording to its function.

DAMPERS IN HVAC
Zone control dampers play a part in a much larger zone control HVAC
system. This system controls the dampers to determine how each zone is
heated and cooled. The use of motorized modulating dampers allows the
systemto controlthe air flow automatically.
A back-draft damper allows air to travel one way without travelling the
opposite way. These dampers are often circular and are balanced according
to what direction they are positioned on the wall so that gravity creates a
natural seal. At the same time, they are designed to open as air pushes
against it from the correct direction and close when that airflow is cut off to
prevent any air returning fromthe other direction.

DUCTS IN HVAC?
Ducts or plenums provide the pathways for air. Plenums are more open
spaces for air circulation, while ductworkprovides definedpathways.

THE PLENUM SYSTEM
• Suitedfor a job wherethe roomoutlets are all close to the unit
• Supply diffusers are normally locatedon theinside walls
• Work better on fossil-fuelsystems
• Fossil-fuel supply air temperaturescouldeasily reach130°F
Plenum
system
Return
duct
Supply plenum
Branch
ducts

THE EXTENDED PLENUM SYSTEM
• Canbe appliedto a long structure
• This systemtakes the plenumcloser to the farthest point
• Called the trunkduct system
• Ducts called branches completetheconnection to the terminal units
Living Room
9,000 btu (cooling)
18,000 btu
(heating) 300 cfm
100
cfm
100 cfm
200 cfm
100
cfm
200
cfm
50
cfm
100
cfm
50 cfm

PERIMETER LOOP SYSTEM
Well suitedfor installationin a concrete floor in a colder climate
Warmair is in the whole loop whenthe furnace fan is running
Keeps the slab at a more even temperature
Provides the same pressure to all outlets
Living Room
9,000 btu (cooling)
18,000 btu
(heating) 300 cfm
100
cfm
100 cfm
200 cfm
100
cfm
200
cfm
50
cfm
100
cfm
50 cfm

DUCTS IN HVAC
There mustalways be a supply path and a return or exhaust path.
The return path generally brings used air back to be recycled into the
building but mixed with some percentage of outside air to maintain
freshness. This saves energy, as it avoids conditioning more outside
air. However, some laboratories and other programs require 100% outside
air for healthand safety.
Plenums can provide less resistance to airflow and have slower-moving
air. While this can be advantageous, they can also be more expensive and
are not appropriatefor space-constrainedbuildings.

DUCTS IN HVAC
There must always be a supplypathand a return or exhaust path.
The return path generally brings used air back to be recycled into the building but
mixed with some percentage of outside air to maintain freshness. This saves energy, as it
avoids conditioning more outside air. However, some laboratories and other programs
require 100%outside air for healthandsafety.
Plenums can provide less resistance to airflow and have slower-moving air. While this
can be advantageous, they can also be more expensive and are not appropriate for space-
constrained buildings.

DUCT MATERIALS
• Ductworkmust meet local codes . In India it
IS 655:2006
• For years, galvanized sheetmetal was used exclusively
• Other ductworkmaterials
Aluminum
Fiberglass duct-board
Spiral metal duct
Flexible duct

FLEXIBLE DUCTS
Comes in sizedup to about 24 in. in diameter.
Some have a reinforcedaluminumfoil backing
Some come withvinyl or foil backing and insulationon it
Keepduct runs as short as possible
Has more friction loss inside it thanmetal duct
Flex duct shouldbe stretched as tightas possible

FLEXIBLE DUCTS
Floor
Register
Flexible Duct
Damper Supply
Return

DUCT AIR MOVEMENT
Branchducts are fastened to the maintrunkby a takeoff-fitting
The takeoff encourages the air moving the duct to enter the takeoff to the
branch duct
Air moving in the duct has inertia, meaning it wants to move in a straight
line
Using turning vanes will improve theair-flowaroundcorners

Low Velocity Duct Systems: Low-velocity ducts are characterized by air
velocities in therange of 400 to 2000 feet per minute (fpm).
Medium Velocity Duct Systems: Medium-velocity (MV) duct systems are
characterizedby air velocities in therange of 2000 to 2500fpm.
High Velocity Duct Systems: High-velocity (HV) duct systems are
characterizedby air velocities in the range of 2500 to 3500 fpm.
DUCT CLASSIFICATION

Low-velocity ductwork design is very important for energy efficiency in air
distributionsystems.
Low-velocity design will lead to larger duct sizes, but it may be worth since,
doubling of duct diameter will reduce friction loss by a factor of 32 times and
will be less noisy.
The low-velocity systems occupy more space and have higher first costs;
facility owners are often reluctant to provide the space for more expensive
ductwork, but significant energy savings can be realized even when the
ductworkis only increasedby one standardsize.
DUCT CLASSIFICATION

DUCT CLASSIFICATION
Some guidelines for determining the maximumairflowvelocityto use in selected
applications of low-velocitysystems include:

 Source Components : Boilers, Chillers, Furnace,
Cooling Towers.
HVAC COMPONENTS

 Distribution Components: Ducts, Pumps, Dampers, Splitters, Turning Vanes, Fan.
HVAC COMPONENTS

 Delivery Components : Diffuser, Register, Grille, Baseboard Radiator, Convector ,
Personal Climate control
HVAC COMPONENTS

LECTURE 6 ZONING IN HVAC.ppt

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