RefrigerationAirConditioning TOTAL LECTUREPPT.ppt

REFRIGERATION
AND
AIR CONDITIONING
Dr. Gbeminiyi M. Sobamowo
Department of Mechanical Engineering
Faculty of Engineering
University of Lagos
Nigeria
LECTURE NOTES

Standard principles
of
REFRIGERATION
AND
AIR CONDITIONING systems

INTRODUCTION
TO
REFRIGERATION
Refrigeration may be defined as the process of removing heat
from a substance under controlled conditions.
It also includes the process of reducing and maintaining the
temperature of a body below the general temperature of its
surroundings.
In other words, the refrigeration means a continued extraction of
heat from a body whose temperature already below the
temperature of its surrounding.

Refrigeration and air conditioning cool without creating heat.
There are no other methods of cooling.
Boiling water only emits heat.
POPULAR MISCONCEPTIONS ABOUT REFRIGERATION
POPULAR MISCONCEPTIONS ABOUT REFRIGERATION

Refrigeration and air conditioning actually transfer heat. The
cool in one area and heat another!
Water evaporators can actually cool dry air.
Certain solid state materials can cool on one side and heat on the
other.
Boiling water absorbs heat when it becomes a gas (water vapor).
Rubbing alcohol cools the skin when it evaporates.
ACTUAL FACTS ABOUT REFRIGERATION
ACTUAL FACTS ABOUT REFRIGERATION

The two main principles for refrigeration and air conditioning
operation are:
Liquids absorb heat, when changing from liquid into gas.
Gases emit heat, when changing from gas into liquid.
In a refrigeration system, liquid refrigerant absorbs heat from the
air when changing to a gas (boiling).
BASIC PRINCIPLES OF REFRIGERATION
BASIC PRINCIPLES OF REFRIGERATION

Refrigerators and air conditioners:
 Remove heat from the air faster than warming sources.
 The removed heat is dissipated to the atmosphere.
BASIC COOLING PRINCIPLES
BASIC COOLING PRINCIPLES

REFRIGERATOR
REFRIGERATOR
In a refrigerator, heat is virtually being removed from a lower
temperature to a higher temperature.
According to the second law of thermodynamic (it is impossible to
construct a device which, operating in a cycle, will produce no effect
other than the transfer of heat from a cooler to a hotter body), this
process can only be performed with the aid of some external work.
It is thus obvious that supply of power (say electric motor) is regularly
required to drive refrigerator.

REVERSED HEAT ENGINE CYCLE
REVERSED HEAT ENGINE CYCLE
A reversed heat engine cycle is an engine operating in
the reverse way, i.e. receiving heat from a low
temperature region, discharging heat to a higher
temperature region, and receiving a net inflow of work.
Under such condition the cycle is called a heat pump or a
refrigeration cycle.

REVERSED CARNOT CYCLE
REVERSED CARNOT CYCLE
In the Reversed Carnot cycle, the refrigerant is first compressed reversibly and
adiabatically in process 1-2 where the work input per kg refrigerant is W0
, then it
is condensed reversibly in process 2-3 where the heat of rejection is Q1
, the
refrigerant then expands reversibly and adiabatically in process 3-4 where the
work output is WE
, and finally it absorbs heat Q2
reversibly by evaporation from
the surroundings in process 4 – 1.

THE IDEAL REFRIGERATION CYCLE : THE CARNOT CYCLE
.The Carnot refrigeration cycle Carnot refrigeration cycle is a completely reversible cycle,
hence is used as a model of perfection for a refrigeration cycle operating between a
constant temperature heat source and sink. It is used as reference against which the real
cycles are compared
Practical difficulties with Carnot refrigeration system:
It is difficult to build and operate a Carnot refrigeration system due to wet compression
due to the presence of liquid. In practice, wet compression is very difficult especially with
reciprocating compressors. This problem is particularly severe in case of high speed
reciprocating compressors, which get damaged due to the presence of liquid droplets in
the vapour.
ii. The second practical difficulty with Carnot cycle is that using a turbine and extracting
work from the system during the isentropic expansion of liquid refrigerant is not
economically feasible, particularly in case of small capacity systems.

PRINCIPLE
OF
VAPOUR COMPRESSION REFRIGERATION SYSTEM
.The Carnot cycle cannot be achieved for the vapour cycle in actual practice because liquid
slugging would occur during compression of the two-phase refrigerant. In addition, the
mixture, mostly liquid, does very little work when it expands after condensation in the heat
engine. Therefore, a single- stage ideal vapour compression cycle is used instead of the
Carnot cycle. In an ideal single-stage vapour compression cycle compression occurs in the
superheated region. A throttling device, such as an expansion valve, is used instead of the
heat engine. Single-stage means that there is only one stage of compression. An ideal cycle
is one in which the compression process is isentropic and the pressure losses in the
pipeline, valves, and other components are negligible.
Vapour compression means that the vapour refrigerant is compressed to a higher pressure,
and then the condensed liquid is throttled to a lower pressure to produce the refrigerating
effect by evaporation. It is different from the absorption or air expansion refrigeration
cycle.

PRINCIPLE OF VAPOUR COMPRESSION REFRIGERATION SYSTEM

Low pressure gas enters the compressor (1)
and leaves the compressor as a high pressure,
high temperature gas.
refrigerant cycle
refrigerant cycle

The high temperature, high pressure gas
flows into the condenser (2) and becomes a
liquid and gives off heat to the outside air.
refrigerant cycle
refrigerant cycle

The liquid then flows under high pressure, to
the expansion valve (3). This valve restricts
the flow of the liquid to lower its pressure as
refrigerant cycle
refrigerant cycle

The low pressure liquid then moves to the
evaporator (4), where heat from the inside
air is absorbed by the liquid changing its
refrigerant cycle
refrigerant cycle

The refrigerant, now a hot low-pressure gas,
moves back to the compressor (1) where the
entire cycle is repeated over and over again.
refrigerant cycle
refrigerant cycle

PRINCIPLE
OF
PRINCIPLE OF VAPOUR COMPRESSION REFRIGERATION SYSTEM
Heat is put into the fluid at the lower temperature and pressure in
the evaporator which provides the latent heat to make it boil and
change to a vapour. This vapour is then mechanically compressed
(by the compressor) to a higher pressure and a corresponding
saturation temperature at which its latent heat can be rejected in the
condenser so that it changes back to a liquid. The total cooling
effect will be the heat transferred to the working fluid in the boiling
or evaporating vessel (evaporator), i.e. the change in enthalpies
between the fluid entering and the vapour leaving the evaporator.

PRINCIPLE
OF
A working system will require a connection between the condenser
and the inlet to the evaporator to complete the circuit. Since these
are at different pressures this connection will require a pressure
reducing and metering valve. Since the reduction in pressure at this
valve must cause a corresponding drop in temperature, some of the
fluid will flash off into vapour to remove the energy for this
cooling. The volume of the working fluid therefore increases at the
valve by this amount of flash gas, and gives rise to its name, the
expansion valve.
.

PRINCIPLE
OF

PRINCIPLE
OF
The refrigeration cycle is shown by the process lines ABCD (Figure
2). Compression is assumed to be adiabatic, but this will alter
according to the type of compressor. Since there is no energy input
or loss within the expansion valve, these two points lie on a line of
equal enthalpy. The pressure–enthalpy chart can give a direct
measure of the energy transferred in the process.
In a working circuit, the vapour leaving the evaporator will
probably be slightly superheated and the liquid leaving the
condenser subcooled. The gas leaving the evaporator is superheated
to point A1 and the liquid subcooled to C1.

PRINCIPLE
OF
Also, pressure losses will occur across the gas inlet and outlet, and
there will be pressure drops through the heat exchangers and piping.
The final temperature at the end of compression will depend on the
working limits and the refrigerant. Taking these many factors into
account, the refrigerating effect (A1 – D1) and the compressor
energy (B1 – A1) may be read off directly in terms of enthalpy of
the fluid. The distance of D1 between the two parts of the curve
indicates the proportion of flash gas at that point. The condenser
receives the high-pressure superheated gas, cools it down to
saturation temperature, condenses it to liquid, and finally subcools
it slightly. The energy removed in the condenser is seen to be the
refrigerating effect plus the heat of compression.

COEFFICIENT OF PERFORMANCE
COEFFICIENT OF PERFORMANCE
Since the vapour compression cycle uses energy to move energy, the ratio of these two
quantities can be used directly as a measure of the performance of the system. This ratio,
the coefficient of performance, was first expressed by Sadi Carnot in 1824 ideal reversible
cycle, and based on the two temperatures of the system, assuming that all heat is
transferred at constant temperature. Since there are mechanical and thermal losses in a real
circuit, the coefficient of performance (COP) will always be less than the ideal Carnot
figure. For practical purposes in working systems, it is the ratio of the cooling effect to the
input compressor power.
The coefficient of performance which is an index of performance of a thermodynamic
cycle or a thermal system. Because it can be greater than 1, “COP” is used instead of
thermal efficiency.
.
.

PRINCIPLE
OF
Subcooling
Condensed liquid refrigerant is usually subcooled to a temperature lower than the saturated
temperature corresponding to the condensing pressure of the refrigerant. This is done to
increase the refrigerating effect. The degree of subcooling depends mainly on the
temperature of the coolant (e.g., atmospheric air, surface water, or well water) during
condensation, and the construction and capacity of the condenser.
Superheating
the purpose of superheating is to avoid compressor slugging damage. The degree of
superheat depends mainly on the type of refrigerant feed and compressor as well as the
construction of the evaporator

PRINCIPLE
OF
.Vapour compression refrigeration systems are the most commonly used among all
refrigeration systems. As the name implies, these systems belong to the general
class of vapour cycles, wherein the working fluid (refrigerant) undergoes phase
change at least during one process. In a vapour compression refrigeration system,
refrigeration is obtained as the refrigerant evaporates at low temperatures. The
input to the system is in the form of mechanical energy required to run the
compressor. Hence these systems are also called as mechanical refrigeration
systems. Vapour compression refrigeration systems are available to suit almost all
applications with the refrigeration capacities ranging from few Watts to few
megawatts. A wide variety of refrigerants can be used in these systems to suit
different applications, capacities etc. The actual vapour compression cycle is based
on Evans-Perkins cycle, which is also called as reverse Rankine cycle. Before the
actual cycle is discussed and analysed, it is essential to find the upper limit of
performance of vapour compression cycles. This limit is set by a completely
reversible cycle.

TYPES OF REFRIGERATION SYSTEM
1. VAPOUR COMPRESSION RERIGERATION SYSTEM
2. VAPOUR ABSOPTION RERIGERATION SYSTEM
3. VAPOUR ADSOPTION RERIGERATION SYSTEM
4. ELECTROLUX REFRIGERATION SYSTEM
5. THERMOELECTRIC REFRIGERATION SYSTEM
6. EJECTOR REFRIGERATION SYSTEM

VAPOUR COMRESSION REFRIGERATION SYSTEM
In an vapour refrigeration cycle, an exanpder or
expansion engine is not used, since power
recovering is small and does not justify the cost of
the engine. A throttle valve or capillary tube is
used for expansion in reducing the pressure from
P1
to P2
.

Actual vapour compression
REFRIGERATION cycle
ACTUAL VAPOUR COMPRESSION REFRIGERATION CYCLE
In order to ascertain that there is no droplet of liquid refrigerant being carried
over into the compressor, some superheating of vapour is used after the
evaporator.
A small degree of subcooling of the liquid refrigerant after the condenser is also
used to reduce the mass of vapour formed during expansion, so that too many
vapour bubbles do not impede the flow and the liquid refrigerant through the
expansion valve.
Both the superheating of vapour at the evaporator outlet and subcooling of
liquid at the condenser outlet contributed to an increase in the refrigerating
effect.

THE FLOW SYSTEM OF
VAPOUR COMRESSION REFRIGERATION CYCLE

A CYCLE DIAGRAM OF A REFRIGERATOR

Refrigerator component functions
1. Compressor: The low pressure and temperature vapour refrigerant from
evaporator is drawn into the compressor through the inlet or suction valve,
where it is compressed to high pressure and temperature. This high pressure
and temperature vapour refrigerant is discharged into the condenser through
the delivery or discharge valve.
2. Condenser: The condenser or cooler consists of coils of pipe in which the
high pressure and temperature vapour refrigerant is cooled and condensed.
The refrigerant, while passing through the condenser, gives up its latent heat
to the surrounding condensing medium which is normally air or water.

Refrigerator component functions
Expansion Valve: It is also called throttle valve or refrigerant control valve. The function
of the expansion valve is to allow the liquid refrigerant under high pressure and
temperature to pass at a controlled rate after reducing its pressure and temperature. Some of
the liquid refrigerant evaporates as it passes through the expansion valve, but the greater
portion is vapourised In the evaporator at the low pressure and pressure.
Evaporator:
An evaporator consists of coils of pipe in which the liquid-vapour refrigerant at low
pressure
and temperature is evaporated and changed into vapour refrigerant at low pressure and
temperature. In evaporating, the liquid vapour refrigerant absorbs its latent heat of
vaporization from the medium (air, water, brine) which is to be cooled. The evaporator
produces the cooling or refrigerating effect.

RefrigerationAirConditioning TOTAL LECTUREPPT.ppt

THE WORKING PRINCIPLES
OF
EVAPORATOR AND CONDENSER
Hot
Fluid
Cold
Fluid

THE WORKING PRINCIPLE OF AN EVAPORATOR

THE WORKING PRINCIPLE OF A CONDENSER

CONDENSER
EVAPORATOR?
An evaporator is a heat device or heat exchanger that is
used in to cool a space by extracting heat from the space
and transfer the heat to a low temperature liquid through
its tube
Tube
Fins
Evaporator Fan
Temperature Sensor
Evaporator Battery

The Purpose
The purpose of the evaporator is to receive the low-pressure and temperature liquid from the
expansion valve and convert this liquid into gas, while extracting heat from the space to be
cooled.
The Parts
The evaporator consists of pipes, usually made of cooper and cooling fins usually made of
aluminum.
The Process
In the evaporator, the refrigerant turns into gas at low pressure and temperature, while
absorbing heat from the space to be cooled. The cooling down is done by the evaporator,
which the air from the refrigerated area and blows it through the evaporator fines. When the
air has passed through the evaporator fins and gave up its heat, it returns to the refrigerated
area a lot cooler and drier. As the refrigerant evaporates, the vapor is returned to the suction
side of the compressor via the suction line.
Therefore, it could be stated stepwisely that in evaporator:
the refrigerant turns into a low pressure and temperature gas that could absorb heat.
 the evaporator blower sucks in relatively hot air from the refrigerated area/space to be cooled.
 the relatively hot air passes through the evaporator fins and is cooled by the low pressure and
temperature gas by means of heat exchanging process.
EVAPORATOR : The Purpose, the Parts, the Process

CONDENSER
CONDENSER?
An condenser is a heat device or heat exchanger that is used
to receive the high-pressure and temperature gas from a
source and converts the gas into liquid, while emitting heat
to the sink/surroundings.
Tube
Fins
Condenser Fan
Temperature Sensor
Condenser Battery

The Purpose
The condenser function is the opposite of the evaporator function. The purpose of the
condenser is to receive the high-pressure and temperature gas from the Compressor
and convert this gas into liquid, while emitting heat to the surroundings.
The Parts
The condenser consists of pipes, usually made of cooper and cooling fins usually
made of aluminum.
Process
The refrigerant in its gas state flows through the condenser pipes, while the air from
the surrounding is (by cooling ) around the fins.
CONDENSER : The Purpose, the Parts, the Process
It could stated stepwisely that the condenser:
Gets high pressure and temperature refrigerant gas from the compressor.
Converts the gas to a liquid at the outlet of the condenser by heat exchanging process
Uses fins to enhance the rate of heat transfer from the primary surfaces, the tubes
Additionally, a fan can be used to increase heat transfer to the outside.
Therefore, it acts as a radiator that heats the outside environment .

FINS! WHAT FOR?
Fins are employed to enhance the heat transfer rate between the primary surface and
its conductive, convective, radiative environment. In refrigeration and air
conditioning systems, refrigerant flows through the evaporative tubes absorbing heat
from the surrounding air to maintain a temperature below the surrounding or
refrigerant flows through the condenser tubes emitting heat to the surrounding air.
As the outer surface of the evaporator/condenser is air, the fin surface are commonly
employed to reduce the convective resistance at the air side of the heat exchanger
Fins

FANS! WHY?
The fan's purpose is to move the air through the evaporator or the condenser. The heat
exchange depends upon the temperature difference between the air and the refrigerant. The
greater the difference will be, the greater will be the heat amount that is exchanged between
the air and the refrigerant.
When the fan operates at its higher speed, it delivers its greatest volume of air across the fins
and coils for a rapid evaporation. As the area is cooled down, it will soon reach a temperature,
in which little extra cooling will result, if the fan is allowed to continue at its high-volume
flow. A reduction in the fan speed will decrease the airflow volume but the lower volume rate
will allow the air to remain in contact with the fins and coils for a longer period of time and
give up its heat to the refrigerant.
Fan

The compressor:
• Circulates the refrigerant in the circuit.
• Compresses the refrigerant that leaves the evaporator.
• Raises its temperature to enable heat transfer to the outside.
COMPRESSOR

Electricity energizes the motor to rotate
the compressor crankshaft. Reciprocating
compressors have a cylinder, piston,
connecting rod, crankshaft, cylinder head
and valves. The operating cycle is shown
in the diagram.
On the down stroke of the piston, a low pressure area is created
between the top of the piston, the cylinder head and the suction line
of the air conditioning evaporator. Cold refrigerant vapor rushes
through the suction valve inlet and into the low pressure area
WORKING PRINCIPLE OF COMPRESSOR

HOW DOES IT WORK?
The exhaust (discharge) valve is forced
open with the increasing pressure. The
vapor is compressed and forced into the
discharge (high) side of the refrigeration
system.
On the up stroke, the suction valve closes
and piston decreases the volume of the
refrigerant gas, thus increasing its
pressure.

60
HOW DOES IT WORK?
When the piston reaches the top of the cylinder, the discharge valve
closes, and the suction valve opens as the piston starts down again
drawing in cold refrigerant vapor to complete the cycle.
Note that the connecting rod attached between the crankshaft and piston serves to change
rotary motion into reciprocating (back and forth) motion.

61
HOW DOES IT WORK?
The piston rings prevent the vapor from escaping between the
piston and cylinder walls and improve the operating efficiency.
The compressor housing or crankcase contains the bearing
surfaces for the crankshaft and stores the oil that lubricates the
compressor parts.

62
THERMAL EXPANSION VALVE
The thermal expansion valve (TEV or TXV):
• Main objective: To regulate refrigerant flow
• Also achieves:
• Increased outlet pressure from the compressor
• Reduced pressure to the evaporator
• Lowers the temperature of the liquid coolant
• Regulates the cooling output of the evaporator
• Prevents ice formation on the evaporator pipes

63
How does the TEV or TXV work:
As the thermostatic expansion valve regulates the
rate at which liquid refrigerant flows into the
evaporator, it maintains a proper supply of
refrigerant by matching this flow rate against how
quickly the refrigerant evaporates (boils off) in
the evaporator coil.
To do this, the TEV responds to temperature of the refrigerant vapor as
it leaves the evaporator (P1) and the pressure in the evaporator (P2).
It does this by using a movable valve pin against the spring pressure
(P3) to precisely control the flow of liquid refrigerant into the
evaporator (P4):

Pressure Balance Equation
P1+P4 = P2+P3
P1 = Bulb pressure (opening force)
P2 = Evaporator pressure (closing force)
P3 = Superheat spring pressure
(closing force – usually adjustable)
P4 = Liquid pressure (opening force)
To do this, the TEV responds to temperature of the refrigerant vapor as
it leaves the evaporator (P1) and the pressure in the evaporator (P2).
It does this by using a movable valve pin against the spring pressure
(P3) to precisely control the flow of liquid refrigerant into the
evaporator (P4):

• This “flash gas” has a high degree of energy transfer, as sensible
heat of the refrigerant is converted to latent heat.
• The low pressure liquid and vapor combination moves into the
evaporator, where the rest of the liquid refrigerant “boils off” into a
gas as it absorbs heat from its surroundings.
When the flow of the liquid refrigerant is
restricted by the valve pin:
• The pressure on the liquid refrigerant
drops.
• A small amount of liquid refrigerant is
converted (boils) to gas, due to the drop in
pressure.

From the CYCLE to the P-H diagrams

REFRIGERATION SYSTEM SCHEMATIC

The hidden parts of a
REFRIGERATION SYSTEM

VAPOUR COMRESSION REFRIGERATION
SYSTEM

MULTISTAGE VAPOUR COMPRESION SYSTEM
For a given condensation temperature, the lower the evaporator temperature, the
higher becomes the compressor pressure ratio. For a reciprocating compressor, a
high pressure ratio across a single stage means low volumetric efficiency (ratio
of the act volume of gas drawn at evaporator pressure and temperature to the
Piston displacement). Also, with dry compression the high pressure ratio results
in high compressor discharge temperature which may damage the refrigerant. To
reduce the work of compression and improve the COP, multistage compression
with intercooling may be adopted.

In refrigeration plant where different temperatures are required to be
maintained at vapour points in the plant such as in hotels, large
restaurants, institution, industrial plants and food markets where the food
products are received in large quantities and stored at different
temperatures e.g. fresh fruits, fresh vegetables, fresh cut meats, frozen
products, diary products, canned goods, bottle goods all have different
conditions of temperature and humidity for storage. In such case, multiple
evaporators and compressors are needed since each location is cooled by
its own evaporator in order to obtain more satisfactory control of the
location.

The absorption cycle is a process by which refrigeration effect is produced through the use of
two fluids and some quantity of heat input, rather than electrical input as in the more familiar
vapor compression cycle.
The refrigeration system working on vapour absorption cycle was developed by a
Frenchman, Ferdinand Carré, and brought to the US during the Civil War when the North
cut off the supply of natural ice from the South.
Heat-driven system: work input is very low, but a larger heat input is required
More expensive and complex, larger, less efficient than vapor-compression systems
Used when unit cost of heat (thermal energy) is low or thermal energy is available that would
otherwise be wasted
Used primarily in large commercial and industrial applications
May include a secondary loop for safety reasons and for ease and cost of set-up
vapour absoption refrigeration system

VAPOUR ABSOPTION REFRIGERATION SYSTEM

vapour absoption refrigeration system

SIMPLE SCHEMATIC DIAGRAM OF vapour absoption refrigeration cycle

Step or operation principle of vapour absoption system
Low pressure vapor from evaporator is absorbed by liquid solution in absorber.
This process is exothermic. If heat weren’t removed, the temp would rise and
absorption would cease.
Absorber is cooled by water or air.
Low pressure liquid is pumped to a higher pressure and enters the generator.
Heat from a high temp source drives the vapor out of the liquid
The liquid returns to the absorber through a throttling valve, returning to a low
pressure.
The high-pressure vapor is sent to a condenser, expansion valve, and then the
evaporator.

COMMON REFRIGERANTS USED IN VAS
• Ammonia-water systems, ammonia is the refrigerant
• Water-lithium bromide , water is the refrigerant
• Water-lithium chloride , water is the refrigerant
• R134a-DMac

vapour absoption refrigeration cycle

Some liquids like water have great affinity for absorbing large quantities of certain vapors (NH3) and
reduce the total volume greatly. The absorption refrigeration system differs fundamentally from vapor
compression system only in the method of compressing the refrigerant. An absorber, generator and pump
in the absorption refrigerating system replace the compressor of a vapor compression system. Figure 6.7
shows the schematic diagram of a vapor absorption system. Ammonia vapor is produced in the generator
at high pressure from the strong solution of NH3 by an external heating source. The water vapor carried
with ammonia is removed in the rectifier and only the dehydrated ammonia gas enters into the condenser.
High pressure NH3 vapor is condensed in the condenser. The cooled NH3 solution is passed through a
throttle valve and the pressure and temperature of the refrigerant are reduced below the Refrigeration
Cycles temperature to be maintained in the evaporator. The low temperature refrigerant enters the
evaporator and absorbs the required heat from the evaporator and leaves the evaporator as saturated
vapor. Slightly superheated, low pressure NH3 vapor is absorbed by the weak solution of NH3 which is
sprayed in the absorber as shown in the Fig. Weak NH3 solution (aqua–ammonia) entering the absorber
becomes strong solution after absorbing NH3 vapor and then it is pumped to the generator through the
heat exchanger. The pump increases the pressure of the strong solution to generator pressure. The strong
NH3 solution coming from the absorber absorbs heat form high temperature weak NH3 solution in the
heat exchanger. The solution in the generator becomes weak as NH3 vapor comes out of it. The weak
high temperature ammonia solution from the generator is passed to the heat exchanger through the
throttle valve. The pressure of the liquid is reduced to the absorber pressure by the throttle valve.
working principle of nh3-h20 vapour absorption refrigeration system

Ammonia vapor passes through the condenser, expansion valve, and evaporator.
In the absorber it reacts with and is absorbed by the water in an exothermic reaction. Heat is
removed with cooling water.
Solution is pumped to the regenerator, increasing the pressure.
Heat is added in the regenerator, and ammonia and a little water vaporizes.
Ammonia and water vapor are separated in the rectifier. Ammonia goes to the condenser &
water is returned to the regenerator.
Hot liquid solution goes through a regenerator, where some heat is transferred to the liquid
leaving the pump.
The now somewhat cooler liquid goes through an expansion valve, taking it to a lower
pressure and temperature
summary of the working principle of nh3-h20 vas

LECTURE 2
REFRIGERANTS
AND
MONTREAL PROTOCOL

THE DEFINITION AND History of refrigerants
1800–1900 Ethyl alcohol, methyl amine, ethyl amine, methyl chloride, ethyl chloride, sulphur dioxide, carbon dioxide, ammonia
1900–1930 Ethyl bromide, carbon tetrachloride, water, propane, isobutene, gasoline, methylene chloride
1931–1990 Chlorofluorocarbons, hydrochlorofluorocarbons, ammonia, water
1990–2010 Hydrofluorocarbons, ammonia, isobutene, propane, carbon dioxide, water
Immediate future Hydrofluorooelifins, hydrofluorocarbons, hydrocarbons, carbon dioxide, water
According to ASHRAE standard 34-1978, Refrigerant is defined as the medium of heat transfer in a refrigerating system
which picks up heat by evaporating at low temperature and pressure and gives up heat on condensing at higher
temperature and pressure.
Many of the refrigerants used during the early periods did not survive, mainly due to their toxicity. Ammonia, however,
continues to be a refrigerant of choice for food freezing applications even today in spite of its toxicity, mainly due to its
excellent thermodynamic and thermal properties. Carbon dioxide used in the early days of refrigeration is again being
considered as a refrigerant in spite of its high operating pressures. Hydrocarbons used in the early part of the last century
were quickly discontinued because of their flammability. However, hydrocarbons have made a successful comeback and
are being used extensively in small domestic refrigerators and freezers in recent years. The discovery of CFCs in the late
twenties revolutionized the refrigeration industry. Both CFCs and hydrochlorofluorocarbons (HCFCs) are non-toxic,
possess excellent thermodynamic properties, and are non-flammable. Both CFCs and HCFCs dominated the
refrigeration industry for nearly 70 years till the Montreal Protocol imposed a ban due to their contribution to ozone
depletion. In the last two decades, hydrofluorocarbons (HFCs), which possess zero Ozone Depletion Potential (ODP),
have gradually replaced CFCs. Very recently, global warming due to emission of various gases into the atmosphere has
been the issue being dealt with by the Kyoto Protocol HFCs which have high Global Warming Potential (GWP) are also
being banned in spite of the fact that they are ozone friendly. Hydrofluorooelifins (HFOs), which have very low GWP
and invented
very recently are expected to replace HFCs in many applications. A detailed discussion on the different refrigerants is
given below.

INTRODUCTION
Over the years, there have radical changes in the selection and use of
refrigerants, mainly in response to the environmental issues of ‘holes in the
ozone layer’ and ‘global warming or greenhouse effect’. These refrigerants
include R11, R12, R22, R502 and ammonia (R717) of which only ammonia is
considered environmentally friendly, but it is not readily suited to commercial
or air-conditioning refrigeration applications because of its toxicity,
flammability and attack by copper.

refrigerants from different chemical group

IDEAL Refrigerant PROPERTIES
Ideal properties for a refrigerant for vapour compression cycles
The requirements for the working fluid are as follows:
1. A high latent heat of vaporization
2. High density of suction gas
3. Non-corrosive, non-toxic and non-flammable
4. Critical temperature and triple point outside the working range
5. Compatibility with materials of construction, with lubricating oils, and with other materials present in the
system
6. Convenient working pressures, i.e. not too high and preferably not below atmospheric pressure
7. High dielectric strength (for compressors having integral electric motors)
8. Low cost
9. Ease of leak detection
10. Environmentally friendly
No single working fluid has all these properties and a great many different chemicals have been used over the
years. The present situation has been dominated by the need for fluids which are environmentally friendly.

Refrigerants APPLICATIONS
TYPICAL USES OF REFRIGERANTS BEFORE 1987
TYPICAL APPLICATION REFRIGERANTS RECOMMENDED
Domestic refrigerators and freezers R12
Small retail and supermarkets R12, R22, R502
Air-conditioning R11, R114, R12, R22
Industrial R717, R22, R502, R13B1
Transport R12, R502

Global warming potential
Global warming potential (GWP)
Global warming is the increasing of the world’s temperatures, which results
in melting of the polar ice caps and rising sea levels. It is caused by the
release into the atmosphere of so-called ‘greenhouse’ gases, which form a
blanket and reflect heat back to the earth’s surface, or hold heat in the
atmosphere. The most infamous greenhouse gas is carbon dioxide (CO2),
which once released remains in the atmosphere for 500 years, so there is a
constant build-up as time progresses.
The main cause of Carbon dioxide emission is in the generation of
electricity at power stations. Each kWh of electricity used in the UK (as
example) produces about 0.53 kg of the gas and it is estimated that
refrigeration compressors in the UK consume 12.5 billion kWh per year.

OZONE DEPLETION POTENTIAL
AND
MONTREAL PROTOCOL
Ozone depletion potential (ODP)
The ozone layer in our upper atmosphere provides a filter for ultraviolet
radiation, which can be harmful to our health. Research has found that the
ozone layer is thinning, due to emissions into the atmosphere of
chlorofluorocarbons (CFCs), halons and bromides.
THE MONTREAL PROTOCOL in 1987 agreed that the production of these
chemicals would be phased out by 1995 and alternative fluids developed.
From Table 3.1, R11, R12, R114 and R502 are all CFCs used as
refrigerants, while R13B1 is a halon. They have all ceased production within
those countries which are signatories to the Montreal Protocol. The situation
is not so clear-cut, because there are countries like Russia, India, China etc.
who are not signatories and who could still be producing these harmful
chemicals.

SET DATES OF BAN
It should be noted that prior to 1987, total CFC
emissions were made up from aerosol sprays, solvents
and foam insulation, and that refrigerant emissions
were about 10% of the total. However, all the different
users have replaced CFCs with alternatives. R22 is an
HCFC and now regarded as a transitional refrigerant,
in that it will be completely phased out of production
by 2030, as agreed under the Montreal Protocol. A
separate European Community decision has set the
following dates.

The atmosphere is divided into layers defined by the distance above the surface of the earth
as follows:
0–15 kilometers (Troposphere)
15–50 kilometers (Stratosphere)
50–85 kilometers (Mesosphere)
•
>85 kilometers (Thermosphere)
A proportion of the sun’s energy is emitted as ultraviolet (UV) radiation which can be
divided into three types according to the wave length:
UVA : 3200 – 4000 Å
UVB : 2900 – 3200 Å
UVC : < 2900 Å (1 Å = 10–10m)
Ozone depletion effects

Ozone depletion effects
The short wavelength bands of the UV radiation are harmful to the life on earth in many ways. A layer
of the stratosphere, 20–40 km thick and rich in ozone, filters out a major portion of this harmful UV
radiation from reaching the earth’s surface. Chemically stable chlorofluorocarbon (CFC) refrigerant
molecules remain for a very long time in the atmosphere and can therefore reach the ozone layer. In the
stratospheric area an energetic UV photon strikes the CFC molecule. The energy of the impact releases a
chlorine atom, which is chemically very active and reacts with an ozone molecule. Through this
interaction, the ozone molecule is destroyed. This is a complicated chain reaction leading to the ‘ozone
hole’.
Health and environmental effects of ozone depletion can be multifarious. Because biological life on this
planet evolved only after the ozone shield developed, enormous potential for harm exists if the shield is
damaged. DNA, the genetic code present in all living cells is damaged by UV radiation, UVC being the
most damaging. A significant reduction in ozone in the upper atmosphere could result in long-time
increase in skin cancer and cataracts, and probably damage the human immune system. Environmental
damage and the resulting economic losses could be because of decreased yields of major agricultural
crops, and reduced productivity of phytoplankton with possible implications for the aquatic food chain,
resulting in substantial losses at the larval stage of many fish (e.g. anchovies, shrimps and crabs)
The extent of damage that a refrigerant can cause to the ozone layer is quantified by the Ozone
Depletion Potential (ODP), which is the ratio of impact caused by the substance on ozone to that caused
by CFC 11.

SET DATES FOR Refrigerant BAN
• 1/1/2000 CFCs banned for servicing existing plants
• 1/1/2000 HCFCs banned for new systems with a shaft input power greater
than 150kW
• 1/1/2001 HCFCs banned in all new systems except heat pumps and
reversible systems
• 1/1/2004 HCFCs banned for all systems
• 1/1/2008 Virgin HCFCs banned for plant servicing

NEWLY DEVELOPED REFRIGERANTS
HFCFC/HFC service-blends (transitional alternatives)
R401A R401B R409A
HFC–Chlorine free (long-term alternative)
R134A
HFC–Chlorine free–blends–(long-term alternatives)
R404A ISCEON 59 R407A R407B
R407C R410A R411B
Halogen free (long-term alternatives)
R717 ammonia R600a R114 R290 R1270

AMMONIA AND THE HYDROCARBONS
Ammonia and the hydrocarbons
These fluids have virtually zero ODP and zero GWP when released into the atmosphere
and therefore present a very friendly environmental picture. Ammonia has long been used
as a refrigerant for industrial applications. The engineering and servicing requirements are
well established to deal with its high toxicity and flammability.
There have been developments to produce packaged liquid chillers with ammonia as the
refrigerant for use in air-conditioning in supermarkets, for example. Ammonia cannot be
used with copper or copper alloys, so refrigerant piping and components have to be steel
or aluminum. This may present difficulties for the air conditioning market where copper
has been the base material for piping and plant. One property that is unique to ammonia
compared to all other refrigerants is that it is less dense than air, so a leakage of ammonia
results in it rising above the plant room and into the atmosphere. If the plant room is
outside or on the roof of a building, the escaping ammonia will drift away from the
refrigeration plant.

AMMONIA AND THE HYDROCARBONS
The safety aspects of ammonia plants are well
documented and there is reason to expect an increase in
the use of ammonia as a refrigerant.
Hydrocarbons such as propane and butane are being
successfully used as replacement and new refrigerants for
R12 systems. They obviously have flammable
characteristics which have to be taken into account by
health and safety requirements. However, there is a
market for their use in sealed refrigerant systems such as
domestic refrigeration and unitary air-conditioners.

TOTAL EQUIVALENT WARMING IMPACT
The newly developed refrigerant gases also have a global warming potential if
released into the atmosphere. For example, R134a has a GWP of 1300, which
means that the emission of 1 kg of R134a is equivalent to 1300 kg of CO2. The
choice of refrigerant affects the GWP of the plant, but other factors also
contribute to the overall GWP and this has been represented by the term total
equivalent warming impact (TEWI). This term shows the overall impact on the
global warming effect, and includes refrigerant leakage, refrigerant recovery
losses and energy consumption. It is a term which should be calculated for each
refrigeration plant. Other newly developed refrigerants include R404a HFC
R407c HFC R410a HFC R411b HCFC R717 ammonia R290 propane R600a
isobutene R1270 propylene

REFRIGERANT BLENDS
REFRIGERANT BLENDS
Many of the new, alternative refrigerants are ‘blends’, which have two or three components,
developed for existing and new plants as comparable alternatives to the refrigerants being replaced.
They are ‘zeotropes’ with varying evaporating or condensing temperatures in the latent heat of
vaporization phase, referred to as the ‘temperature glide’ improving plant performance, by correct
design of the heat exchangers.
Blends or mixtures are used either to obtain different desired properties such as bubble point
temperature, oil solubility, flammability, as drop-in-substitutes for older refrigerants that are no longer
produced, etc. by combining different fluids or to obtain variable temperature refrigeration. The
mixtures used in refrigeration systems can be divided into four categories, namely, azeotropes, near-
azeotropes, zeotropes and very wide boiling zeotropes.

Chloroflurocarbons (CFC)
These are fully halogenated fluids that have high ODP and were found to be the most responsible for the
creation of ozone hole. Use of formerly popular CFCs such as R12 and R11 in ne equipment was banned
by the Montreal Protocol. While R12 recovered from old systems may still be available, new lots of
CFCs are no longer being produced.
Hydrochlorofluorocarbons (HCFC)
Unlike fully-halogenated CFCs, which contain only carbon and halogen atoms, in the case of partially-
halogenated HCFCs, not all hydrogen atoms are replaced by halogen atoms. The remaining hydrogen
atoms facilitate partial breakdown of the compounds in the troposphere. For this reason these compounds
are less harmful to the stratospheric ozone layer, though they still have the some potential to damage the
ozone layer. However, since they are known to cause global warming, HCFCs are no longer used in the
industrialized countries of the West. Phase-out of HCFCs (mainly HCFC22, which is still widely used in
India) is being accelerated.
Hydrofluorocarbons (HFC)
Hydrofluorocarbons contain fluorine but no chlorine or bromine in the molecule, so that their ODP is
zero. Some examples of HFCs are R23, R32, R125, 134a, 143a and 152a. A problem with HFCs is that
they are chemically stable and can accumulate in the atmosphere contributing to the global warming.
Hence, HFCs need to be eventually replaced.

Hydrofluorooelifins (HFO)
These also belong to a class of HFCs, but are derived from unsaturated hydrocarbon molecules such as propylene. HFOs
are relatively unstable, have a small atmospheric lifetime and therefore a small GWP. R1234yf and R1234ze are two
HFO refrigerants invented recently. R1234yf has been widely accepted for use in cars by the automobile industry
because of its very low GWP of 4. As soon as it becomes commercially available, R1234yf is expected to replace
R134a, which is currently being widely used in air-conditioning plants, automobile air conditioners, domestic
refrigerators, etc. There are also attempts to find mixtures of R1234yf and other HFCs such as R32 for use in other
applications such as domestic air conditioners since mixtures containing R1234yf will have low GWP, typically less
than 1000.
Fluoroiodocarbons (FIC)
These are a group of chemicals containing fluorine, iodine and carbon such as, trifluoromethyl iodide (CF3I)
perfluoroethyliodide (C2F5I) and perfluoropropyl iodide (C3F7I). The FICs are reported to have zero ODP and negligible
GWP due to their very short life periods. These can also be used in blends. A blend of C3F7 and HFC 152a (51/49 mole
percent) was run in a refrigerator without oil change for over 1,500 hours without apparent ill effects. Measurements
showed that the energy efficiency and capacity were equal to or slightly better than CFC 12.
Hydrocarbons
Several hydrocarbons have excellent thermodynamic properties and can be used as refrigerants. Though alkanes,
ketones, alcohols and ethers can be used, alkanes are the most preferred group. As already mentioned, the main concern
is that most of the hydrocarbons are flammable. Here, one should note that in certain industrial applications
hydrocarbons have been used as refrigerants since the beginning of the 20th century. Hydrocarbons, for instance, are
used in pure or mixture forms as refrigerants in petrochemical plants and in gas liquefaction plants. In LNG plants,
mixtures of methane and n-pentane are in common use. With adequate safety precautions flammability will not pose a
major problem in the usage of hydrocarbons. Home refrigerators have been sold in tens of millions worldwide,
including India, during the last twenty years. The ODP of hydrocarbons is zero, while their GWP is very small.

Natural Inorganic Fluids
Ammonia is an environmentally safe but toxic working fluid which is attracting renewed attention. It possesses the
most advantageous thermodynamic and thermo-physical properties needed for refrigeration. Ammonia-based
compression systems, mainly for low temperature applications, are well developed.
These are generally suited for industrial surroundings where sufficient knowledge and facilities exist to handle chemical
leaks. There are proposals to extend its use into areas occupied by common public (e.g., comfort air conditioning,
cooling of display cases in food shops, heat pumps, etc.). But this requires careful planning and design to avoid panic
and accidents in case of leaks.
Water has many desirable characteristics for cooling applications such as: thermal and chemical stability, neither toxic
nor flammable, high COP and high heat transfer coefficients. Disadvantages of water include sub-atmospheric pressure
operation, large specific compressor displacement, limitations of evaporation temperatures above 0°C and problems of
lubrication.
Air has been used commercially for aircraft cooling since a long time. In spite of the low COP, this is being used
because of the operating conditions (e.g., availability of compressed air and ram effect) and stringent specifications
(e.g., low weight, small size, absolute safety, zero toxicity, etc.) which are exclusive to aircrafts. In the light of the new
situation created due to the ban on synthetic refrigerants, possible use of air for on-ground applications is being
considered actively. It should be noted here that the technology with air as refrigerant will be totally different from that
with other working fluids due to the fact that air does not undergo phase change (condensation/evaporation) at the
temperature levels encountered in conventional refrigeration applications.
Use of carbon dioxide as refrigerant dates back to the early years of refrigeration. It is environmentally benign. Being
the by- product of many energy conversion processes, it is cheap and easily available. Its use as a refrigerant can reduce
its release to the atmosphere, thereby making a positive contribution to the environment. Very high operating pressure is
a drawback. Because of its low critical point, most of the thermodynamic cycle operates in the single phase region.
Since CO2 enters the expansion valve as a superheated vapour, it results in a large energy loss during the throttling
process. Carbon dioxide is an excellent refrigerant when both heating and cooling are desired. Also, it is not preferable
for use in tropical countries such as India due to the high ambient temperatures which result in high condensing

Comparison of different refrigerants

conclusion
Thus, there are no refrigerants in the horizon that completely meet the safety,
stability, energy efficiency and environmental friendliness. It seems that the
refrigeration industry will have very little choice but to use flammable refrigerants
(HFOs, low GWP HFCs, HCs, NH3, etc). Since the energy efficiency of HFOs is
somewhat low, mixtures of medium GWP fluids such as R32 and low GWP
refrigerants such as R1234yf may be the working fluids of choice in the immediate
future. Meanwhile, the quest for better molecules continues. Barring new
inventions, natural refrigerants appear to be the best choice in the long term.

LECTURE 4
AIR-CONDITIONING SYSTEM

Evaporator
Condenser
Compressor
Expansion Valve
Blower Fan
A Window Unit Air-Conditioning System

RADIANT AND CONVECTIVE LOADS
.

AIR CONDITIONING CLASSIFICATION
.
CLASSIFICATIONS OF AIR CONDITIONING SYSTEM
BASED ON MAJOR FUNCTION
Comfort and industrial air conditioning systems.
BASED ON THE SEASON OF THE YEAR
Summer, Winter and Year Round air conditioning system
BASED ON THE EQUIPMENT ARRANGEMENT
Central, Unitary and Combined central and unitary

PRINCIPLE OF AIR-CONDITIONING SYSTEM
.

SOME INDOOR AND OUTDOOR PARTS
OF A CENTRAL AIR-CONDITIONER
.

SOME INDOOR AND OUTDOOR PARTS OF A CENTRAL AIR-
CONDITIONER
.

SOME INDOOR AND OUTDOOR PARTS OF A CENTRAL AIR-
CONDITIONER WITH THE DUCT SYSTEM
.

COOLING BY THERMAL STRATIFICATION
.

MIXED MODE VENTILATION
. APPLICATION OF MIXED MODE VENTILATION
By combining natural ventilation and comfort cooling,
the Mixed Mode system really does offer the best of
both worlds. Natural ventilation is the preferred low
energy strategy option for commercial buildings. Air
conditioning can provide the close climate control
desired in periods of occasional hot or cold weather.
The Mixed Mode cooling system combines these two
elements, providing the benefits of both-energy
efficiency and improved comfort.

CONCURRENT MIXED MODE OPERATION
.
In concurrent mixed-mode operation, the air conditioning
systems and the operable windows operates in the same space
and at the same time.

MIXED-MODE OPERATION SYSTEM
.
In this mixed-mode operation, the building “change-over”
between natural ventilation and air-conditioning on a seasonal or
daily basis.

ZONED MIXED-MODE OPERATION SYSTEM
.
In zoned operation system, different zones within
the building have different conditioning strategies.

MIXED MODE VENTILATION SYSTEM
.

ADVANTAGES OF MIXED-MODE IN BUILDINGS
.
ADVANTAGES OF MIXED-MODE BUILDINGS
Reduced HVAC energy consumption
Higher occupant satisfaction
Highly “tunable” buildings
Mixed mode can be useful in places where natural
ventilation is not suitable (e.g very cold weather) where
fully mechanically ventilated rooms are not available.

BENEFITS OF MIXED-MODE VENTILATION
.BENEFITS OF MIXED-MODE VENTILATION
•Energy savings
•Thermal comfort
•Health and productivity
WHY AREN’T WE SEEING MORE MIXED-MODE BUILDINGS?
•Building design issues
•Building operations and controls issues
•Fire and safety concerns
•Energy code concerns

CENTRAL AIR-CONDITIONING SYSTEM
.

CENTRAL AIR CONDITIONING SYSTEM
.

CENTRAL AIR CONDITIONING SYSTEM
.A Central air conditioning unit commonly is an air
conditioning system that uses ducts to distribute cooled
and dehumidified air to more than one room, or uses
pipes to distribute chilled water to heat exchangers in
more than one room and which is not plugged to a
standard electrical outlet.
•The components of a central air conditioning unit are;
the refrigerant, coil, the evaporator, the compressor,
the condenser, the expansion device and the plenum.

CENTRAL AIR-CONDITING SYSTEM
. OPERATING SYSTEM OF CENTRAL AIR-CONDITIONER
The centralized cooling system is outfitted by
ducts for the distribution of air in all sections
of the space to be cooled. The air is cooled by
pipe lines that are chilled. The setup of the
central cooling system automatically reduces
the sound created by its operation as it is
installed outside of our homes.

TYPES OF CENTRAL AC
. •Field Erected Systems
These are usually used in large commercial structures. They may also be
used to heat and cool various sections of a large building. Field erected
systems frequently use chilled or heated liquid to transfer heating and
cooling.
•Central or Unitary Systems
Central air conditioning systems are ideal for residential air conditioning.
They are a complete, manufactured package ready for assembly. All
internal wiring and piping has been done. The condensing unit is located
away from the evaporator. There are three evaporator designs in use:
•The A-type evaporator
•The slant-type evaporator
•The flat-type evaporator for horizontal flow

CENTRAL AIR CONDITIONING WITH DUCT
.

PRINCIPLE
OF
. .
QUESTION?

RefrigerationAirConditioning TOTAL LECTUREPPT.ppt

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