DEPARTMENT OF TECHNICAL AND VOCATIONAL EDUCATION

ME-31017
REFRIGERATION AND AIR CONDITIONING I
SEMESTER – I

A.G.T.I (THIRD YEAR)

BY
DR. SU THET MON THAN
ASSOCIATED PROFESSOR
 CONTENTS
Chapter Title Page No

1 INTRODUCTION 1

2 VAPOUR COMPRESSION SYSTEM 9

3 REFRIGERATION EQUIPMENTS 26
4 ASSEMBLE PARTS OF A DOMESTIC 45
REFRIGERATOR AND TROUBLESHOOTING
APPENDIX
REFERENCES
 CHAPTER 1
INTRODUCTION

1.1 Meaning of Refrigeration

Refrigeration is the process of maintaining the temperature of a space or a system
lower than the ambient temperature. Thus, it requires continuous removal of heat from the
system at a lower temperature, and to reject it at a higher temperature.
To produce and maintain temperatures lower than the ambient, energy has to be spent.
In most of cases, this energy is in the form of mechanical work. The requirement of energy
for producing refrigeration is in accordance with the second law of thermodynamics. Thus a
refrigeration system has to obey the first law as well as the second law of thermodynamics.
1.2 Development of Refrigeration
Preservation of food is one of the most important uses of refrigeration. Food lasts
longer when kept in cool areas. Studied show that food have microbes that multiply faster in
warm places. This multiplication of microbes had been recognized as the major cause of food
spoilage. At the temperature of 50ºF or less, microbes could not multiply at all.
Refrigeration was first used by Chinese when they discovered that ice improves the
taste of drinks. The early Egyptians found out that water could be cooled by placing it in jars
on roof top at sundown. The Greeks and the Romans place their foods in snow for
preservation purposes. In warm places, people place their foods in vessels emmersed in
streams of water or by storing them in holes dug at the ground for preservation.

Figure 1.1 Ice Box Refrigerator

Since little was known about the procedures on how to lower the temperature enough
to freeze water into ice, ice was then transported. The value of ice for the preservation of
foods had been recognized for hundreds of years. An ice box was used as the refrigerator
during that time. It was the first refrigerator introduce to the society.
 2

It was in 1834 when an American Engineer, Jacob Perkins introduced the first patent
for a practical ice-making machine in London. These machines were used successfully in
meat-packing plants. Within the next fifty years, ice-makers were manufactured in the United
States, France, Germany, and in other countries. Nowadays, Refrigeration is not only put in
use for the preservation of foods. It is likewise used in chemicals, metals, medicines, gases,
machines, tools and electronic devices.

1.3 Law of Thermodynamics

The law of Thermodynamics is concerned about the conservation of energy. It places
no limit on the amount or direction of the conservation.
When work is done to overcome friction, it is dissipated as heat. All the work energy
can be converted to heat energy, but if an amount of heat energy were available, it would not
be possible for all of this to be converted into work.
We know from experience that when two systems with different temperature are in
contact, heat will transfer from the system with higher temperature to the one with lower
temperature, and not in the opposite direction, i.e., from the colder system to the hotter one.
Thus, energy conversion may wholly take place in one direction, but only partly take
place in one direction. Also it is possible for an energy transfer to take place in one direction,
but not at all possible in the opposite direction.
1.5 Heat Engine
It is a thermodynamic cycle which develops net positive work as a result of heat
transfer from a hotter body to a cooler body. For example, internal combustion engines, gas
turbine, steam power plant, etc.

TH Hot Reservoir

(Heat source)
QH
Heat Engine
Wnet(net work output)

QL

Cold Reservoir
TL
(Heat sink)
Figure 1.2 Work and heat transfer for a heat engine
 3

Net Work
Thermal efficiency 
Heat supplied

Wnet QH  QL Q
 th    1 L
QH QH QH

QL
 th  1 
QH
If all the processes making up the above cycle are reversible, and the heat is
transferred in and out of the cycle reversibly, then the heat engine is a reversible heat engine.
If this reversible heat engine runs backward so that work is input to the cycle and heat
is rejected at the high temperature, that we have a heat pump or a refrigerator.
This occurs inside a pipe or coil of tubing, positioned so that the latent heat required
can be extracted from the space to be cooled.

1.4 Reversed Carnot Cycle as a Refrigerator

Any reversible heat engine cycle when operated in the reversed direction will work as
a refrigerator. Thus, the reversed Carnot cycle will absorb heat Q L from a low temperature
body at temperature TL. The work W has to be supplied in accordance with the second law of
thermodynamics. The heat removed from the low temperature body, the refrigerating effect,
along with the work done will be rejected to the high temperature reservoir at temperature T H.
This heat rejected QH will be equal to QL+W, to satisfy the first law of thermodynamics. The
schematic arrangement and the T-S diagram of the Carnot refrigerator is shown in Figure 1.3.
From this diagram,

Hot Reservoir
TH
(Heat source)

QH
TH
Refrigerator

Wnet(required work input)

TL

QL = (desired output)

Cold Reservoir
TL
(Heat sink)

Figure 1.3 Reverse Carnot Cycle as a Refrigerator

 4

Q1 = TL (s1 – s4) = area under process line 4-1

Q2 = TH (s1 – s4) = area under process line 2-3
Work done = area 1-2-3-4 = (TH – TL ) (s1 – s4)
The performance of the refrigerating machine is expressed in terms of a parameter
called coefficient of performance or COP, which is defined as

(COP)ref = = = =

The same machine could be used for heating. Thus, it will remove heat from a low
temperature ‘source’ at TL, and along with the work W will supply heat Q2 at higher
temperature TH for heating purposes. In this case the machine is termed as heat pump.

Hot Reservoir
TH
(Heat source)

QH= (heating effect)

Heat Pump

Wnet(required work input)

QL

Cold Reservoir
TL
(Heat sink)

Figure 1.4 Reverse Carnot Cycle as a Heat Pump

The COP or the heat pump is defined as

(COP)heat pump = =

= =

It can be seen that the COP of the heat pump is related to the COP of a refrigerator as
below:

(COP)heat pump = = =

= (COP)ref + 1
 5

Coefficient of heat pump, (COP)heat pump, is also termed as Energy Performance Ratio,
EPR.
It is evident from the expression for COP that higher the temperature of heat removal,
TL, or lower the temperature of heat rejection, TH , higher will be the COP of the reversed
Carnot cycle working as a refrigerator or as a heat pump.

1.4 Methods of Producing Refrigeration

The various methods of producing refrigeration may be broadly put under two
catergories:
(i) Conventional methods,
(ii) Non-conventional methods.
Amongst conventional methods, air refrigeration system is most suitable for aircraft
cooling. The vapor compression system is much more popular and over 80 percent of
refrigeration all over the world is produced by this method. The other conventional method is
vapour-absorption refrigeration system. This system is particularly adaptable for solar
refrigeration or where waste heat is available.
The non-conventional methods are those which have either a limited use or are still in
development stages. These include:
1. Steam jet refrigeration system.
2. Thermo-electric refrigeration system.
3. Vortex tube system
4. Adiabatic demagnetization

Example (1.1)
For a refrigerating machine of a heat pump, the ratio of TL to TH is 4:5. If the work done on
the cycle is 32 kW, determine the maximum heating effect. If the cycle is used as a heat
engine, determine the engine efficiency and heat rejected.

Solution:

TH

HP W input

TL
 6

TL/TH = 4/5
TL = 0.8 TH
Maximum Heating Effect of Heat Pump = ?
COPHP = QH/ Wnet
COP = TH/ (TH - TL)

=5
QH = COPHP x Wnet = 5 x 32 = 160 kW
Maximum heating effect of heat pump = 160 kW

If the cycle is used as a heat engine

TH

HE W output

TL

ɳ = Woutput/Qinput
Taking control volume, QH = Wnet + QL
Wnet = QH - QL
Since Q = ʃ Tds
ɳ engine = (TH - TL)/TH
= 1- TL / TH
= 1 – 4/5 = 0.2
 7

Tutorial Sheet 1
1. A refrigerator driven by a 0.7457 kW meter removes 21 kJ/min from a cold body. What is
the COP of this refrigeration? At what rate is heat rejected to the hot body?
2. A refrigerator remove an amount of heat equivalent to 1014720 kg of ice/day (latent heat
of fusion of ice is taken as 334 kJ/kg) The COP of this refrigerator is 4. What is the (hp) of
the prime mover driving this refrigerator?
3. Using an engine of 30% thermal efficiency to drive a refrigerator having a COP of 5. What
is the heat input into the engine for each kJ removed from the cold body by the refrigerator?
4. If a refrigerator is used for heating in winter so that the atmospheric becomes the cold body
and the room to be heated becomes the hot body, how much heat would be available for
heating for each kilowatt input into the driving motor? The COP of the refrigerator is 5, and
the electro-mechanical efficiency of the motor is 90%. How dose compare with resistance
heating.
5. A Carnot refrigerator rejects 2500 kJ of heat at 80ºC while using 1100 kJ of work. Find (a)
the cycle low temperature (b) COP (c) Amount of heat absorbed.
6. A Carnot refrigerator operates between temperature limits of -5ºC and 30ºC. The power
consumed is 4 kW and the heat absorbed is 30 kJ/kg. Determine (a) COP (b) Refrigerant flow
rate.
7. A Carnot engine has a thermal efficiency of 25% as a power engine. It is reversed and does
950 kJ/min of refrigeration. Determine: (a) The work and COP
(b) If this system is used for heating. What is the amount of heat delivered and the COP for
heating? Is more work required than (a)?
(c) What is the difference if the heat is added to the system at 4ºC? or at -50ºC
8. Two reversible engines operate in series between a high temperature (TH) and a low
temperature (TC) reservoir. Engine A rejects heat to engine B which in turn rejects heat to the
low temperature reservoir. The high temperature reservoir supplies heat to engine A. Let
TH=1000 K, TC=400 K and the engine thermal efficiency are equal. The heat receives by
engine A is 500 kJ. Determine:
(a) temperature of heat rejection by engine A
(b) work or engine A and B
(c) heat rejected by engine B
9. A carnot refrigerator requires 1.3 kW per tonne of refrigeration to maintain a region at low
temperature of -38 ºC. Determine:
(i) COP of Carnot refrigerator
(ii) Higher temperature of the cycle
 8

(iii) The heat delivered and COP when this device is used as heat pump.
Assume 1 tonne of refrigeration = 14000 kJ/hr.
10. A machine works on reversed Carnot cycle between -10 ºC and 24ºC. Find its COP when
working as a (i) heat engine, (ii) refrigerator, (iii) heat pump.
 9

CHAPTER 2
VAPOUR COMPRESSION SYSTEM

2.1 Ideal Vapour Compression Refrigeration Cycle

Vapor compression refrigeration plant is shown in Figure 2.1. The working substance
is such that readily evaporates and condenses. The cycle is thermodynamically assumed such
that the refrigerant vapor leaves the evaporator and enters the compresor as dry saturated
vapor. This point is denoted as point 1 both on the following diagram shown.
The T.S diagram is shown in Figure 2.1. When the vapor is dry saturated at the
suction to the compressor cylinder during its suction to the compressor, locate the point as 1
where it is at pressure P1 and temperature T1.
The vapor is drawn in the compressor cylinder during its suction stroke and during the
compression stroke the vapor is compressed isentropically to pressure P2 and temperature T2
and delivered out from the compressor.
This point is represented by 2, point 2 shows the vapor in superheated state. The
vapor at condition 2 passes on to condenser in which cooling water is supplied to remove heat
from the vapor. Thus vapor is first cooled to the saturated temperature at pressure P2 and
further removal of heat, condenses it to liquid removing its latent heat till point 3 is reached.
Thus in order to carry out this operation, the saturation temperature corresponding to
pressure P2 should be sufficiently higher than the temperature of cooling water for efficient
heat transfer.
The high-pressure liquid is now expended through a throttle valve, and the liquid at 3
throttles to lower pressure P1 and the condition obtained after the constant enthalpy expansion
is shown at 4. After throttling we get the liquid partly evaporated at lower temperature T4 and
lower pressure P1.
Thus, after the throttle valve, we get wet vapor at a low temperature. These vapors
now pass through the evaporator coils immersed in brine or the chamber to be refrigerated.
These vapors absorb latent heat from brine in further evaporating itself. The vapors may
reach condition 1 i.e., dry saturated at pressure P1. These complete the cycle.
By using simple saturated cycle as a standard against which actual cycles may be
compared, the relative efficiency of the actual refrigerating cycles at various operating
conditions can be readily determined.
 10

Figure 2.1 Ideal Vapour Compression Refrigeration Cycle

2.2 The pressure Enthalpy Diagram

The condition of the refrigerant in any thermodynamic state can be represented as a
point on the p-h diagram. This point may be located if any two properties of the refrigerant at
that state are known.
Once the state point has been located on the diagram, the other properties of the
refrigerant for that state can be determined.
The p-h diagram is divided into three regions that are separated from each other by
the saturated liquid and saturated vapor lines.

Absolute
Pressure,
P(Mpa)

Sub cooled Region of phase change

region (liquid vapour mixture) Superheated
(in the form of region
Liquid to vapour (in the form of
liquid)
superheated vapour)
Vapour to liquid

Saturated
liquid Saturated vapour
curve curve
Specific Enthalpy,
h(kJ/kg)

Figure 2.2 The pressure Enthalpy Diagram

The area on the chart to the left of the saturated liquid line is called the sub cooled
region. At any point on the sub cooled region, the refrigerant is below the saturation
temperature corresponding to its pressure. The area to the right of the saturated vapor line
is the superheated region and the refrigerant is in the form of a superheated vapor. The
section of the chart between the saturated liquid and the saturated vapor lines is the mixture
(or wet vapor) region.
 11

This represents the change in phase of the refrigerant between the two saturation lines,
the refrigerant is in the form of a liquid-vapor mixture.
The distance between the two saturations lines along the any constant pressure line, as
read on the enthalpy scale at the bottom of the chart, is the latent heat of vaporization of the
refrigerant at that pressure (hfg). On the chart the change in phase from liquid to vapor phase
takes place progressively from left to right, whereas the change in liquid line, the liquid vapor
mixture is primarily liquid, whereas close to the saturated vapor line, the liquid vapor mixture
is primarily vapor.
The nature of curves for saturated liquid and saturated vapor is dependent on how the
latent heat of vaporization varies with pressure. Both these curves will finally meet tat ta
point and the pressure corresponding to that point is the critical pressure at which liquid
changes to superheated vapor and the latent heat of vaporization is zero.
The lines of constant quality, extending from top to bottom through the center section
of the chart and approximately parallel to the saturated liquid and vapor lines, indicate the
percentage of vapor in the liquid vapor mixture. i.e. The dryness fraction.
For example, at any point along the constant quality line closet to the saturated liquid
line, the quality of the liquid vapor is 10%, (dryness fraction = 0.1) the indicated quality of
the mixture at any point along the constant quality line closet to the saturated vapor line is
90% and the dryness fraction is 0.9. The horizontal lines extending across the chart are lines
of constant pressure and the vertical lines are lined of constant enthalpy.
In the sub cooled region, the constant temperatures lines are nearly vertical and
parallel to the constant enthalpy lines. In the central region, bounded by the saturated liquid
and saturated vapor line, the temperature line is horizontal and parallel to constant pressure
lines, because the refrigerant changes its phase from liquid to vapor at constant pressure and
temperature.
In the superheat region, the temperature lines again change direction and fall sharply
to the bottom of the chart. The lines, very nearly straight, extending diagonally and almost
vertically across the super heated vapor region are constant entropy lines.
In this cycle liquid refrigerant is introduced into an evaporator where it absorbs heat
and boils (evaporates) until it reaches a saturated vapor state. The latent heat, which it
absorbs, causes a cooling effect on its surroundings.
Vapor then passes through the compressor where it is being compressed to a higher
temperature and pressure before entering the condenser, where it is cooled and liquefied. To
complete the cycle the high pressure liquid passes through an expansion valve and returns to
the evaporator at low pressure.
 12

2.3 Cycle Analysis

The standard vapor compression cycle, also known as the saturation vapor
compression cycle, is shown on the pressure-enthalpy diagram in Figure 2.3,
In the basic cycle
1-2 Saturated vapor is compressed isentropically (i.e. s1 = s2) from saturated vapor to
superheated vapor
2-3 High –pressure vapor is liquefied at constant pressure in the condenser to become liquid
3-4 Expansion (pressure reduction) at constant enthalpy (i.e. h3=h4). There is no heat and
work transfer in this process
4-1 Wet vapor enters the evaporator and evaporation takes place at constant pressure until it
becomes a saturated vapor.

To represent Saturated Vapor Compression Cycle on a T-S diagram.

We can analyze the performance of the vapor compression cycle by considering the energy
balance for each of the components. Referring to figure and applying the steady flow energy
equation (SFEE) gives the following:
Compressor (process 1-2)
Applying the SFEE on the compressor gives
Q-W= H2-H1
Where changes in kinetic and potential energy are negligible.
Since the compression process is adiabatic, heat transfer Q is zero. In the compressor, work is
done on the system, Hence W is a negative quantity
Combining the above, the SFEE can be written as:
-(-W) = H2 – H1
W = H2 – H1
W = m (h2-h1)
w = h2 – h1
Where w is the work done by the compressor per second, or the input power to the
compressor, is given by:
Wº = mº (h2-h1) kW
Where mº = mass flow rate of refrigerant in the plant (kg/s)

Condenser (process 2-3)

Applying the steady flow energy equation on the condenser gives
Q-W = H3 – H2
 13

Where changes in kinetic and potential energy are negligible.

Since heat is rejected from the refrigerant in this process, Q is negative, Also, there is no
work transfer in the condenser.
Hence the SFEE can be re-written as:
-Q = H3 – H2
Q = H2 - H3
Q = m (h2- h3)
The rate of heat rejection in the condenser is:
Qº = mº (h2- h3) kW

Expansion (process 3-4)

Since the expansion process in the expansion valve occurs under constant enthalpy, therefore,
h3 = h4
There is no heat nor work transfer in this process.

Evaporator (process 4-1)

Applying the SFEE on the evaporator gives
Q-W = H1- H4
Where changes in kinetic and potential energy are negligible.
Since heat is absorbed by the refrigerant in process 4-1, therefore Q is positive. Also, there is
no work transfer in the evaporator.
Hence the SFEE can be re-written as:
Q = H1- H4
Q = m (h1 – h4)
The rate of heat absorption in the evaporator, which is the cooling capacity of the
refrigeration plant is:
Qº = mº (h1 – h4) kW
And the refrigerating effect (RE) is given by:
RE = (h1-h4)

2.4 Unit of refrigeration

The amount of heat absorbed by the system at low temperature is the refrigerating
effect. Refrigerating effect is compared with production of ice. A short ton 2000 lb of ice
when melting, will give the latent heat of fusion as 2000 (144) = 288,000 B.T.U and thus a
machine capable of producing a net refrigerating effect of 288,000 BTU per 24 hours is
 14

called 1 ton machine. It may be noted that 1 ton refrigerating plant will not produce 1 ton ice,
or the quantity in the evaporator that determines the rating.
1 ton of refrigeration = 12000 BTU/hr
= 200 BTU/min
= 50 kcal/min
= 211 kJ/min
= 3.41 kW
2.5 Actual Vapour Compression Refrigeration Cycle
For thermodynamic analysis of the refrigeration systems, we consider the ideal
behaviour of the fluid and neglect any extraneous factors. In actual practice however, these
factors have significant effect on the COP and refrigerating effect of the refrigeration cycle.
In this section, we go for a detailed analysis of these external factors and their influence on
the overall system performance.
The actual vapor compression cycle is shown in Figure 2.3. With the help of a T-s
diagram for the operating pressure limits p1 and p2. The actual compression follows 1 – 2′
instead causing considerable difference due to the irreversibilities associated with the
compression process 1 – 2.

Again, during condensation and subcooling by about 5 to 10 K (2'-4) in the condenser,

the pressure before throttling drops about of 2%. The throttled condensate enters the
evaporator at a pressure somewhat higher than the evaporator pressure p1. These
irreversibilities cause significant distortion in the ideal cycle, thereby indicating a significant
reduction in the COP. Also, if we consider the suction and discharge losses in the
compressor, the COP value would decrease further.

Figure 2.3 Actual Vapour Compression Refrigeration Cycle

 15

2.6 Volumetric Efficiency

The ratio of actual volume of gas drawn into the compressor (at evaporator
temperature and pressure) on each stoke to the piston displacement is termed “volumetric
efficiency”. If the effect of clearance alone is considered, the resulting expression may be
termed “clearance volumetric efficiency”. The expression used for grouping into one constant
all the factors affecting efficiency may be termed total volumetric efficiency”. The clearance
volumetric efficiency may be calculated with reasonable accuracy, the total volumetric
efficiency is best obtained by actual laboratory tests, although a fair approximation to it may
be calculated if sufficient data are available.
P

3 2

1
4

clearance V
Effective swept volume

Piston displacement or swept volume

Total volume

ɳ cv = =

ɳ cv = 1 + C – C (Pd/Ps)1/n

where , C = clearance ratio =

Total Volumetric Efficiency, ɳ cv = [1 + C – C (Pd/Ps)1/n] x P1/Pa x Ta/T1

Pa, Ta = pressure and temperature of surrounding air (atm condition)
(or)

ɳv=

N = Compressor rpm (single acting (rpm x 1)

double acting (rpmx2))
 16

2.7 Refrigerant Vapour Power Cycle

3 2' 2
P cond

S1 = S2

P evap 4 1

W1-2/kg = h2 – h1 (Compressor)
Q2-3/kg = h2 – h3 (Condenser)
h3 = h4 = hwet = hf + x hfg = hf + x(hg – hf )
Q4-1 /kg = h1 – h4

2.7.1 Dry Saturated Condition

3 2' 2
P cond

S1 = S2

P evap 4 1

h1 = hg (at evaporator outlet)

h3 = h4 = hf (at condenser outlet)
s1 = sg = s2 = sg2’ + Cpv ln (Tsup/Tsat)
h2 = hsuper = hg2’ + CPv (T2 – T2’)
 17

2.7.2 Wet Condition

 Leaving Evaporator, Dry saturated at the end of Compression)

P cond
3 2

S1 = S2

P evap 4 1

h2 = hg (condenser)
h3 = h4 = hf (evaporator)
h4 = hwet
s2 = s1 = swet = sf + x sfg
= sf + x (sg – sf)
h1 = hwet = hf + x hfg
x= dryness fraction or quality

2.7.3 Superheat Condition at Leaving the Evaporator

 at entering the compressor

3 2' 2

S1 = S2

superheat
P evap 4 1' 1

Superheat temperature = ΔT = T1 – T1’

h3 = h4 = hf
At evaporator, s1 = ssuper = sg1’ + Cpv Ln (Tsuper/Tsat)
h1 = hg + Cpv ΔT
At condenser, s1 = s2 = ssuper = sg2’ + Cpv Ln (T2/ T2’)
h2 = hg2’ + Cpv ΔT
 18

2.7.4 Sub-cool Condition

 at leaving condenser, at entering the expansion valve

3 3' 2' 2
P cond

S1 = S2

P evap 4 1

Sub-cool temperature = ΔT = T3’ – T3

h3 = hsubcool = hf – CpL ΔT
h1 = hg
h2 = hsuper = hg2’ + Cpv ΔT
s1 = s2 = sg = sg2’ + Cpv Ln (T2/T2’)

Example 2.1
In a vapour compression refrigeration system using R-12, the evaporator pressure is 1.4 bar
and the condenser pressure is 8 bar. The refrigerant leaves the condenser subcooled to 30ºC.
The vapour leaving the evaporator is dry and saturated. The compression process is
isentropic. The amount of heat rejected in the condenser is 13417 kJ/min. Determine
refrigerating effect (kJ/kg), refrigeration load (tons), compressor power input (kW) and COP.
Show the cycle on a p-h diagram.
Solution:

3 2
P cond

S1 = S2

P evap 4 1

h
 19

Given Refrigerant R-12

Pe = 1.4 bar Pc = 8 bar, T3 = 30ºC
Heat rejected = 13417 kJ/min in condenser
From p-h diagram
h1 = 177 kJ/kg
h2 = 211 kJ/kg
h3 = h4 = 63 kJ/kg
(i) Refrigeration effect = h1 – h4 = (177 – 63) = 114 kJ/kg (Ans)
(ii) Refrigeration load:
m = mass flow rate of refrigerant

= = = 90.65 kJ/min
-

Refrigeration load = = 48.97 tons (Ans)

(iii) Compressor power input = m/60 (h2 – h1 )

-
= kW = 31.36 kW (Ans)

-
(iv) COP = = = = 3.35 (Ans)
-

Example 2.2
A simple refrigerant 134a (tetrafluroethane) heat pump for space heating, operates between
temperature limits of 15 and 50ºC. The heat required to be pumped is 100 MJ/h. Determine:
(i) The dryness fraction of refrigerant entering the evaporator;
(ii) The discharge temperature assuming the specific heat of vapour as 0.996 kJ/(kg)(K);
(iii) The theoretical piston displacement of the compressor;
(iv) The theoretical power of the compressor
The specific volume of refrigerant 134a saturated vapour at 15ºc is 0.04185 m3/kg.
The other relevant properties of R-134a are given below:

Solution:
20
 21

Tutorial Sheet 2
1. A refrigerator uses refrigerant R12 as the working fluid and operates on an ideal vapour-
compression cycle between 0.14 and 0.8 MPa. If the mass flow rate of the refrigerant is 0.05
kg/s, determine (i) the rate of heat removal from the refrigerated space and the power input to
the compressor, (ii) the heat rejection rate to the environment and (iii) the COP of the
refrigerator.

2. A vapor compression refrigeration plant use ammonia and has the pressure limits of 2 bar
and 8 bar. The evaporator outlet temperature is 7ºC. Compression is polytropic with n= 1.2
and compressor has 2% clearance. The mass flow rate of refrigerant is 8.6 kg/min. determine
the refrigerating effect (tons) and volumetric efficiency of the compressor. If this
refrigeration plants is used as a heat pump, determine its COP.

3. In a vapour compression refrigeration system using R-12, the evaporator pressure is 1.4 bar
and the condenser pressure is 8 bar. The refrigerant leaves the condenser subcooled to 30ºC.
The vapour leaving the evaporator is dry and saturated. The compression process is
isentropic. The amount of heat rejected in the condenser is 13417 kJ/min. Determine
refrigerating effect (kJ/kg), refrigeration load (tons), compressor power input (kW) and COP.
Show the cycle on a p-h diagram.

4. A vapour compression system works on a simple saturation cycle with F12 as the
refrigerant while operates between condenser temperature of 40ºC and an evaporator
temperature of -5ºC. For the modified cycle the evaporator temperature is changed to -10ºC,
and other operating conditions are the same as the original cycle. Compare the power
requirements for both cycles. Both systems develops 15 tons of refrigeration.

5. In a small locally- produced paper factory, the heating requirements amount to a total of 6
KW. It is desired to provide this heat from an existing ice plant which was a Freon- 12 vapor-
compression refrigeration system. You are required to determine:
(a) Size of the compressor required
(b) Power of compressor required.
The following design specifications are to be assumed:
Single acting, single cylinder, air-cooled reciprocating compressor speed 500 rpm.
- stroke/ bore ratio is 1.25
- clearance 2%
 22

- combine mechanical and motor efficiency 81%

(a) The coefficient of performance of the refrigerate
(b) the mass flow of the refrigerant in kg/hr.
(c) the cooling water required by the condenser in kg/hr if the cooling water
temperature rise is limited to 12ºC. Take the specific heat capacity of water =
4.187 KJ/ kg K.

Saturated Pressure Specific Volume Specific Enthalpy Specific entropy

Temperature KN/m2 m3/kg KJ/kg KJ/kgK
ºC Vf Vg hf hg Sf Sg
-10 177 0.00102 0.233 45.4 460.7 0.183 1.762
45 967 0.00115 0.046 133.0 483.6 0.485 1.587

6. A vapor compression refrigeration uses methyl chloride and operates between the pressure
limit of 214 KN/m2 and 852 KN/m2. The compressor which is single acting has a bore of 100
mm and a stroke 125mm. It runs at 5 rev/sec and has a volumetric efficiency of 80%. At the
commencement of isentropic compression, the refrigerant is dry saturated and after
compression it has a temperature of 85ºC. In the condenser, the refrigerant is condensed but
no under cooled. Determine,
(a) The coefficient of performance
(b) The mass of refrigerant
(c) The refrigerant effect
(d) The power of the compressor
The relevant properties of methyl chloride as follows:

Saturated Pressure Specific Volume Specific Enthalpy Specific entropy

Temperature KN/m2 m3/kg KJ/kg KJ/kgK
ºC Vf Vg hf hg Sf Sg
-5 214 0.00103 0.195 53.1 463.3 0.212 1.742
40 852 0.00113 0.052 124.8 482.1 0.495 1.600

7. A vapor compression refrigeration uses methyl chloride. The low pressure suction has a
pressure of 177 KN/m2 and the high pressure section has a pressure of 567 KN/m2. The
compressor is single acting and rates at 240 rev/min. it has two cylinder each of 60 mm bore
and 75 mm stroke. Each cylinder has a volumetric efficiency of 75%. Leaving the
compressor, this refrigerant is dry saturated and its leaves the condenser under cooked by
 23

5ºC. Assuming the compression is isentropic and the expension is constant enthalpy.
Determine
(a) the dryness fraction of the refrigerant entering the compressor
(b) The coefficient of performance
(c) ) the mass flow of the refrigerant in kg/min.
The relevant properties of methyl chloride as follows:

Saturated Pressure Specific Volume Specific Enthalpy Specific entropy

Temperature KN/m2 m3/kg KJ/kg KJ/kgK
ºC Vf Vg hf hg Sf Sg
-10 177 0.00102 0.233 45.4 460.7 0.183 1.762
25 567 0.00110 0.046 100.5 476.8 0.379 1.642
 26

CHAPTER 3
REFRIGERATION EQUIPMENTS

The prime purpose of refrigeration is to produce the desired temperature within a

specific area by transferring heat to a location where it is not wanted. To understand how
these processes are carried on, one must understand the system to accurately diagnose any
trouble.
Refrigeration system is divided into two sections- the Mechanical Section and the
Electrical Section. The Mechanical Section includes the compressor pumping system, the
evaporator, the condenser, the expansion valve, and other miscellaneous parts like the
accumulator, strainer-drier or receiver. The Electrical Section includes the compressor motor,
the overload protector, relay, cabinet bulb and switch, the thermostat, and the heaters.

3.1 Mechanical Section

Four stages of Refrigeration System
1. Evaporator
2. Compressor
3. Condenser
4. Expansion Valve
Two pressure sides of the Refrigeration System
1. Low pressure side
2. High pressure side

Figure 3.1 Schematic Diagram of a Refrigeration System

 27

3.1.1 Six Principal Components of Vapor-compression System

Figure 3.2 Pictorial Diagram of the Refrigeration System

Evaporator: a coil of tube, usually aluminum tube, where heat is being absorbed, thus
changing liquid refrigerant into gas refrigerant (evaporation). It is commonly called freezer of
chiller.
Accumulator: a storage tank which traps liquid refrigerant coming from the evaporator and
prevent it from flowing into the compressor. Liquid refrigerant can damage the compressor.
Compressor: it is called the Hermetic compressor which means that the compressor motor
and its pumping system is sealed in one unit. It is called the “heart” of the system because it
circulates the refrigerant into the system; it also compresses the low pressure refrigerant into
high pressure refrigerant.
Condenser: also a coil of tube, usually made of steel, where the heat being absorbed by the
evaporator inside the cabinet will be discharged into the atmosphere, thus changing the high
pressure gas refrigerant into high pressure liquid refrigerant (condensation).
Strainer-drier: it filters dirt or tiny particles that can cause clogging in the system; it also
absorbs moisture inside the system.
Capillary tube: it is one type of expansion valve made of a small diameter with a length of 8
to 12 ft. It serves as the metering device that controls the flow of the refrigerant into the
evaporation.
Heat Exchanger: the suction line and the capillary tube are soldered to one another so that
the heat inside the capillary tube of high pressure as well as high temperature liquid
refrigerant will be absorbed by the lower temperature-pressure gas refrigerant into the suction
line.
 28

3.2 Evaporators
The evaporator in the vapor compression cycle is a heat exchanger which absorbs
heat from the substance to be cooled and transfers it to boiling refrigerant.
3.2.1 Types of Evaporators
Evaporators are also classified as flooded type and Dry type depending upon whether
liquid refrigerant covers all heat transfer surfaces or some portion is having gas being
superheated. The evaporators with thermostatic expansion valve will have some portion of
heat transfer surface where superheating is taking place and can be designated as dry
evaporator; where as evaporators with float valve will be flooded type.
3.2.1.1 Flooded Type
This type consists of a horizontal shell with tubes and removable end covers. The
liquid to be cooled is pumped through the tubes and a series of passes is arranged to increase
the liquid velocity and heat transfer rate by fitting rate of the end cover (the type shown is a
two pass arrangement). Liquid refrigerant is fed into the shell by an expansion valve capable
of maintains a fined liquid level. The balance pipe shown connects to the expansion valve and
assists the flow of liquid out of the valve chamber.

Flooded Shell & Tube Liquid Cooler

Figure 3.3 Flooded Type

This type of evaporator has two main advantages;
(a) The end covers can be easily removed to facilitate tube cleaning .It is therefore
frequently used where the liquid being cooled is liable to form deposits.
(b) A very high heat transfer rate is obtained .The lower tubes are in contact with liquid
refrigerant. The upper tubes are kept wet by the very violent boiling action with
occurs.
Its primary disadvantages are:
(a) The vapour returning to the compressor is liable to be in a wet condition, particularly
if the liquid level in the shell is too high. Provision must be made to evaporate this
liquid before it reaches the compressor or a type should be used which will tolerate
liquid. (This will usually have a lower operating efficiency.
 29

(b) Oil circulating around the system will enter the shell with the liquid refrigerant but not
evaporate. This result in an increase in the dissolved oil concentration, so that an oil
rectifier.
(c) If the evaporating temperature fall below the freezing point of the liquid being cooled,
ice formation will reduce the heat transfer and flow rates. The evaporating
temperature will then fall rapidly and the liquid free in the tube and cause extensive
damage.
These disadvantages can be overcome by using a dry expansion cooler, which is
the type most commonly fitted to modern liquid cooling plants.
3.2.1.2 Dry Expansion Type

Dry Expansion Shell & Tube Liquid Cooler

Figure 3.4 Dry Expansion Type

Dry expansion is constructionally similar to the flooded type except that the liquid to
be cooled is circulated over the outside of the tubes. A series of baffles insure that the liquid
is brought into contact with the maximum tube surface as it passes through the shell.
The liquid refrigerant is fed into an end cover and evaporates as it pass through the
tubes, in a single pass arrangement , to emerges as a dry vapour before being draw into the
compressor. Although the heat transfer rate is lower that of the flooded type, this type
overcomes the problem associated with flooded evaporator previously described.
(a) Dry vapors are always returned to the compressor.
(b) The vapour returns the oil in circulation to the compressor suction.
(c) Ice formation cannot cause fracture of the tubes.
3.3Compressor
A machine providing gas at high pressure is called a compressor and work must be
done upon the gas by external agency.
3.3.1 Refrigerant Compressor
It takes in refrigerant gas at low pressure or evaporator pressure compresses it and
delivers the high-pressure gas to the condenser. It must be driven by some of prime mover.
 30

HEAT TO RADIATION
HEAT REJECTED AND COOLANT

RRIME COMPRESSOR
WORK
MOVER

HEAT
LOW PRESSURE
AIR COMPRESSED
SOURCE AIR

Figure 3.5 General Arrangement of the Compressor Set

It serves as the re-claiming agent. The vapours are sucked from the evaporator,
compressed to the pressure corresponding to a saturation temperature, which will be higher
than the coolant available to condense it. The other function is to continuously circulate the
refrigerant through the system. The capacity of the compressor determines the capacity of the
refrigeration system.

3.3.2 Types of Compressor

There are mainly three types of compressors used for refrigeration systems:
1. Reciprocating compressor
2. Rotary compressor
3. Centrifugal compressor
4. Helical-rotary-screw compressor
3.3.3 General Applications
 In a reciprocating compressor, a piston travels back and forth (reciprocating) in a
cylinder.
 In a rotary compressor, an eccentric rotates within the cylinder.
 In a centrifugal compressor, a rotor (impeller) with many blades rotating in a
housing, draws in vapor and discharges it at high velocity by centrifugal force.
 In a helical-rotary-screw compressor, there is a pair of special helical rotors.
Theyrap and compresses air as they revolve in an accurately machined compressor
cylinder.
 31

Figure 3.6 Types of Compressor

3.3.3.1 Reciprocating Compressor
Reciprocating compressors are available in sizes as small as 1/12 kW, which are used
in small domestic refrigerators up to about 150 kW for large capacity installations.
The reciprocating compressors are classified as:
i. Open type
ii. Sealed or hermetic type and
iii. Semi – sealed or semi- hermetic type
A reciprocating compressor is usually a piston-cylinder type of pump. The main parts
include a cylinder, piston, connecting rod, crankshaft, cylinder head, and valves. As the
piston goes down, the suction valve opens and it lets the refrigerant come into the cylinder,
while the discharge valve is closed. When the piston moves up, the suction valve will close
while the discharge valve opens letting the refrigerant flow out.

Figure 3.7 Operation of Reciprocating Compressor

3.3.3.2 Rotary Compressor
Three types of rotary compressors are propularly used. They are:
i. Blade Type
ii. Vane Type
iii. Screw Type
 32

The parts of a rotary compressor are the blade, cylinder eccentric, roller, rotor shaft
and the spring.

Figure 3.8 Operation of Rotary Compressor

3.4 Condenser
The condenser is a device that transfers heat from the refrigeration system to the
atmosphere. It is the door through which the unwanted heat flows out of the system.
3.4.1 Types of Condenser
There are mainly three types of compressors used for refrigeration systems:
1. Air-cooled condenser
2. Water-cooled condenser
3. Evaporative condenser
3.4.1.1 Air-cooled Condensers
The refrigerant circulates through a coil and air flows across the outside of
the tubing. The air motion may be caused by natural convection effects when the
air is heated. Thus it can be assumed as a fan to increase the airflow rate resulting
greater capacity.
This type of condenser is usually made of copper or steel tubing with fins
attached which increase the effective area of heat dissipation surface. For
domestic use, the condenser is usually air -cooled by natural convection. Air
surrounding the condenser will be warmer than the air in the room. This warm air
will rise and cooler air will flow into take its place. Some condensing units use motor driven
fan to force air over the condenser tubing and to increase the cooling effects on the
condenser. Two typical shapes of air-cooled condensers namely flat coil finned type and
spiral coil finned type are shown in figures. They are usually used for small capacity
application, which are seldom more than 7 TR because of high head pressure and
 33

comparatively high kW power/ton and the fan vibration and noise. The Capacity of an air-
cooled condenser may be calculated using one of the two basic methods.
The total external area of the condenser can be used to compute its heat dissipating
capacity. Computations based upon what is called the frontal area of the condenser. Using the
total external area of the condenser for dissipating heat depends upon the following variables:
 External area
 Temperature difference
 Time
 Air velocity
Using these values, the capacity of an air- cooled condenser varies between 20
kJ/hrm2Cto 80 kJ/hrm2C. The effect of air velocity is to increase the condenser capacity
with increase in air velocity. A single tube condenser has a total area approximately 20 times
its frontal area.

(a) Flat-coiled Finned Type (b) Spiral-coiled Finned Type

Figure 3.9 Air-cooled Condenser
3.4.1.2 Water Cooled condenser
In watercooled condensers, the cooling water is piped to a watercooling tower, where
its temperature is reduced to the condenser entering temperature. This water from the cooling
tower is circulated through the condenser.
Watercooled condensers are of three basic types,
(i) Double pipe; (ii) shell and tube; (iii) Shell and coil
The double pipe condenser consists of two concentric tubes, one inside the other. The
water passes through the inner tube, and the refrigerant flows through the annulus in the
opposite direction. The double pipe condensers are available in various configurations to suit
the available space and the application.
 34

Figure 3.10 Different Types of Water-cooled Condensers

The shell and tube condenser consists of a cylindrical shell containing a number of straight
tubes held in position at the ends by tube plates. The tubes are made of steel, copper or brass.
The condensing water is circulated through these tubes, whereas the refrigerant is contained
in the shell. Baffles are provided in the shell for proper circulation of refrigerant vapour over
the tubes. Depending upon the number of tube passes and the arrangement o baffles, many
different designs of shell and tube condensers are available.
The shell and coil condensers are made up of bare tubes or finned tube coils enclosed
in a shell. The condensing water is circulated through the coils, and the refrigerant is
contained in the shell.
3.4.1.3 Comparison of Water-cooled and Atmospheric (air cooled) Condensers
Type of Condenser Advantages Disadvantages
Water cooled Low power requirement per ton of Problems of water cost, water
refrigeration. Longer compressor treatment, and water cooling.
life. Cooling capacity is same on a More trouble to install and
hot day as on cooler day. high initial cost.
Air cooled Less maintenance problem, less Higher power requirement
trouble to install, and possible lower per ton of refrigeration.
initial cost. Shorter compressor life. On
hotter days less cooling is
available. Objectionable fan
noise.
 35

From above, it may be concluded that a particular type of condenser may not always
be better for all applications. The selection of condenser depends upon-
(i) System capacity
(ii) Type of refrigerant
(iii) Cooling medium available
3.4.1.4 Evaporative Condenser
An evaporative condenser is essentially a water conservation device and is, in effect, a
condenser and a cooling tower combined into a single unit. A diagram of a typical induced
type evaporative condenser is shown in Figure 3.11.

Figure 3.11 Schematic Diagram of Evaporative Condenser

Both, air and water are employed in the evaporative condenser. The water pumped
from the pump up to the spray header sprays down over the refrigerant coils and returns to
the pump. The air is drawn in from the outside at the bottom of the condenser by action of the
blower and is discharged back to the outside at the top of the condenser. In some cases, both
pump and blower are driven by the same motor. In others, separate motors are used. The
eliminators installed in the air stream above the spray header are to prevent entrained water
from being carried over into the blower.
3.4.1.5 Advantages of Evaporative Condenser (over water-cooled condensers)
The vapour inside the coil is cooled by air as well as by evaporation of spray water.
Therefore, cooling to a temperature below that of ambient air can be achieved. Hence, this
type of condenser reduces the head pressure, and is quite efficient. Plants with capacities of
700 kW cooling (200 tonnes) or above are fabricated using evaporative condensers is less,
 36

and are therefore desirable where wate costs are high and also there is acute shortage of
water.
3.5 Expansion Valve
The expansion valve is a device that controls or limit the flow of refrigerant into the
system. It is installed between the condenser and the evaporator.
3.5.1 Types of Expansion Valve
Common Expansion Devices are:
1. High-side Float
2. Low-side Float
3. Thermostatic Expansion Valve
4. Automatic Expansion Valve
5. Fixed-bore (Capillary Tube)
3.5.2 General Applications
 Thermostatic Expansion Valve (TEV or TXV): control valve in the refrigeration
system operated by the pressure and temperature in the evaporator. Its sensing bulb
which is installed in the outlet of the evaporator monitors the pressure in the
evaporator.
 Automatic Expansion Valve (AEV or AXV): control valve operated by the low-
pressure of the refrigeration system. It is sometimes called “dry” valve due to the fact
that the evaporator is never filled with liquid refrigerant, but just a fog or mist because
of the spraying process that is taking place in it.
 Low-side Float Expansion Valve: is a simple but efficient control valve. It maintains
the constant level of liquid refrigerant into the evaporator.
 High-side Float Expansion Valve: is similar to a Low-side Float expansion valve
where the liquid refrigerant is sorted in the evaporator which makes it flooded, that is
why the evaporator is called the flooded type.
 Capillary Tube: is a control that is made up of small diameter tubes which serves a
constant throttles on the refrigerant.
 37

Figure 3.12 Types of Expansion Valve

Among the five types of expansion valve, the popular type or commonly used control
are the capillary tube, the thermostatic expansion valve, and the automatic expansion valve.
The capillary tube has several advantages among all.
3.6 Filter-drier
Filter-drier is a device in the system that keeps moisture, dirt, metal and chips from
entering the refrigerant control that can restrict the flow or refrigerant into the expansion
valve. It also absorbs moisture which can damage the compressor by means of the absorbent
called Silica gel, alumina gel and synthetic silicates.

Figure 3.13 Filter-drier

3.7 Terms for Refrigerant
Presently, the most common term used for refrigerant is “FREON”. Freon is a
registered trademark of I.I. du Pont Nemours and Company. The two most commonly used
refrigerants or freons are the Freon-12 and the Freon-22.
These two refrigerants are man-made in the sense that nature did not provide a perfect
refrigerant which can be used in our household refrigerator and airconditioner. They are
 38

fluorocarbon synthetic fluids. Two chemists from the University of California studied these
fluids. Irvine suggested in 1974 that molecules of Flourocarbons from more than 1-1/2 billion
aerosol cans sold annualy may be rising into the stratosphere. These gas molecules contribute
to break down the earth’s ozone shield that prevents the sun’s most harmful ultraviolet
radiation from reaching the earth. This radiation, if it gets through, would increase cataracts
as well as human skin cancer, and might even cause genetic damage to plant and animal life.
Freon-12 or R-12 (CCL2F2) has a boiling point of -21.6ºF. This refrigerant is usually
use for household refrigerators and freezers. It is also used in automobile air conditioning as
well as in many commercial and industrial systems. Freon-22 or R-22 (CCC1F2) has a
boiling point of -41.4ºF. It is principally used in airconditioning equipment.

3.7.1 Handling Refrigerants

Liquid refrigerant, if allowed to come in contact with the eyes can cause blindness,
and if it comes in contact with the body, can cause frostbite. If heated, it can buildup pressure
and explode the container. Further, if the refrigerant gets in contact with an open flame, it can
turn into poisonous gas which if enhaled can bring illness to a person. Refrigerants must be
handled with care.
3.7.2 Refrigerant-11 for Flushing the System
R-11 is preferred for use in flushing the system. You can also use R-12 or R-22, but
R-11 has greater advantages than the two. They are:
1. R-11 has a higher boiling point and stays in liquid form up to the temperature of 78ºF.
2. R-11 will not freeze moisture in the system which the other two refrigerants can do.
3. R-11 moves out the moisture and other tiny particles inside the system.
4. R-11 will not cause skin to freeze even if it comes in direct contact with the
refrigerant while the other two can.
Table 3.1 Boiling Temperature and Color code of some Refrigerants
Refrigerant Refrigerant Name Boiling Cylinder
Number Point Color Code
R-11 Trichloromonofluromethane 74.7 ºF Orange
R-12 Dichlorodifluoromethane -21.6 ºF White
R-22 Monochlorotrifluoromethane -41.4 ºF Green
R-500 Refrigerant 152A/12 -28 ºF Yellow
R-502 Refrigerant 22/115 -50.1 ºF Orchid
R-17 Ammonia -28.0 ºF Silver
 39

3.8 Refrigeration Oil

Usually the 1-1/2 bottle of capilla oil in the compressor is used to lubricate all the
moving parts in the system such as the cylinder piston unit. You will observe that a small
amount of oil is circulated with the refrigerant into the system. Oil also uses as coolant for the
compressor. It helps in maintaining the temperature requirement of the compressor.
Do not use motor oil or any oil that is not for refrigeration. Capila oil is manufactured,
refined, free from moisture, wax, sulphur and dirt. Avoid transfering oil from one container to
another. When repairing the compressor, use another bottle of oil rather than use the one
removed from the compressor. Avoid contaminating the oil.
 40

3.9 Electrical Section

The typical electrical components of the refrigerator are:
1. Compressor
2. Relay
3. Overload Protector (O.L.P)
4. Cabinet Bulb and Switch
5. Thermostat
6. Cabinet Heater

Figure 3.14 Schematic Wiring Diagram of a Refrigerator

3.9.1 Compressor
The commonly used compressor motor is the reciprocating compressor. Its size ranges
from 1/12 HP to about 1/3 HP for household refrigeration. It employs a starting winding and
running winding. The running winding is energized during the complete cycle of operation,
wheras, the starting winding is energized only during the starting period, when additional
torque is required to overcome inertia of the unit. It is a single-phase motor.
3.9.2 Single-phase Motor
Types of Single-phase Motor
1. Split-phase Motor
2. Capacitor-start Motor
3. Capacitor-start, Capacitor-run Motor
4. Permanent Capacitor Motor
5. Shaded Pole Motor
Among the five types of motor, the split-phase motor is commonly used in household
refrigeration and sometimes the capacitor-start motor. The shaded pole motor is used for
evaporator fan and condenser fan motor.
 41

Capacitor Start,
Capacitor Run
Motor

Run Capacitor

Figure 3.15 Types of Single-phase Motor

3.9.3 Overload Protector (O.L.P)
The overload protector is a bimetallic overload protector. It is always in series with
the common terminal. Should the current in the motor winding increase to a dangerous value,
the heat developed by a passage of current through the bimetallic overload protector will
cause it to deflect and open the circuit. This will stop the motor before any damage can occur.
After the bimetallic cools, the contact will close and the motor will continue running.

Figure 3.16 Overload Protector

3.9.4 Relays
A compressor starting relay is an electromagnetic mechanism moved by small
electrical currents in a control circuit. It operates a valve or switch on an operating circuit
always connected in series with the starting winding which should be energized only for three
or four seconds at a time. If current flows through it for a longer period, the winding may
overheat which may cause burnout motor. The relay permits electricity to flow through the
starting winding of the motor until the motor reaches about two-thirds of its speed. When this
occurs it disconnect or open the starting winding.
 42

3.9.4.1 Four Types of Relay

1. Current (magnetic)
2. Potential (magnetic)
3. Thermal or Hot Wire Relay
4. Solid State (electronics)

Current Relay

Potential Relay

Solid State Hot-wire Relay

Relay

Figure 3.17 Types of Relay

Current relay and the solid state relay are commonly used in the refrigeration system
especially on a low torque, smaller horsepower motors. The best substitute relay among the
four illustrated is the solid state relay. These relay is not sensitive to the size of the motor as
the others are. These can be used for motor varying from 1/12 to 1/3 hp. The potential relay,
sometimes called, voltage relay, is commonly used with high torque, capacitor-start motors.
The Thermal or hot-wire relay is used also in low-torque, smaller horsepower motors,
especially in the rotary compressor.

Figure 3.18 Wiring Connection using IC Relay in Motor Compressor

3.9.5 Thermostat
The thermostat is an electrical device that controls the temperature. It is the link
between the evaporator and the electrical system. The control mechanism of the thermostat
includes the sensing bulb, which is usually installed at the back of the evaporator, the
 43

capillary tube and the bellows. These three are interconnectely assembled in one which is
charged with a small amount of highly volatile fluid or refrigerant such as the sulfurdioxide.
When the compressor is running and the sensing bulb is gradually cooled, pressure
inside the assembly will decrease, thus opening the contact and cutting the circuit from
electrical source.

Figure 3.19 Thermostat

While the compressor is resting, the sensing bulb will become warm and this will
increase the pressure in the bellows thus closing the contact in the mechanism and running
the compressor. The thermostat will repeat the cycle.
 44

Tutorial Sheet 3
1. What is Evaporator? Describe and Explain types of Evaporator in detail with the help of
neat sketches.
2. What are Compressor and Refrigerant Compressor? Make a sketch for general
arrangement of compressor set, types, and general applications.
3. What is Condenser? Describe types of Condenser and Explain any two types with neat
sketches.
4. With the help of neat sketches, Explain the working principle of Air-cooled Condenser?
5. Write down the Water-cooled condenser in detail.
6. Write down the Evaporative condenser in detail.
7. Describe Advantages and Disadvantages of Water-cooled Condenser compare with Air-
cooled Condenser.
8. What is Expansion Valve? Describe Types and and general applications with the help of
neat sketches
9. Explain Terms for Refrigerant and Handaling Refrigerants.
 45

CHAPTER 4
ASSEMBLE PARTS OF A DOMESTIC REFRIGERATOR AND
TROUBLESHOOTING
4.1 External View and Dimension of Refrigerator

Figure 5.1 Front View Dimension

Figure 4.2 Top View Dimension

 46

4.2 Parts Name of Refrigerator

Figure 4.3 Parts Name of Refrigerator

Lever No. Part Name Quantity

1. Case ice 1
2. Case child 1
3. Lamp cover ( R-shade) 1
4. Refrigerator temperature controller 1
5. Refrigerator Shell ( removable ) 2
6. Glass Shell ( Cover case vegetable ) 1
7. Case vegetable 1
8. Freezer pocket ( T-shade ) 1
9. Freezer pocket ( U-shade) 1
10 Utility pocket ( T-shade ) 1
11. Cause egg 2
12. Bottle pocket ( Large ) 1
13. Bottle pocket ( Small) 1
 47

4.3 Air Flow Diagram of Refrigerator

Figure 4.4 Air Flow Diagram of Refrigerator

Lever Part Name

No.
1. Air circulation in the freezer Compartment
Cold air flow comes out from the upper hole and comes into the lower
hole in louver.
2. Freezer compartment door pocket
Do not store ice cream or frozen food for a long time. Temperature
may rise with frequent opening and closing.
3. Fresh food preserving case (Chilled case)
Used for storing fish or meat.
4. Refrigerator compartment door pocket
The temperature of this position is high. When margarine or something
is stored for 1~2 weeks, you may use refrigerator shelf.
5. Case vegetable
In this vessel and wrap is used to keep them flesh.
6. Freezer room
Do not put in any breakable bottle.
7. Refrigerator room
Do not place frozen food near the duct. It may freeze due to low
temperature.
 48

4.4 Refrigerator Cycle Diagram

Figure 4.5 Refrigerator Cycle Diagram

Lever No. Part Name Quantity

1. Side plate pipe 1
2. Pipe ( Suction ) 1
3. Evaporator 1
4. ACCUM 1
5. Capillary-tube 1
6. Dryer 1
7. Pipe Condenser ( Deliver) 1
8. Compressor 1
9. Pipe condenser ( Suction) 1
10. Hot pipe 1
4.6 Assembly Two Door Linkage

Figure 5.6 Assembly of Two Door Linkage Parts

 49

Lever No. Part Name Quantity

1. Cover ( T-shade ) 1
2. Special screw 3
3. Hinge ( T-shade ) 1
4. Special bolt 2
5. Door switch 1
6. Hinge ( U-shade ) 1
7. Bolt 2

4.6 Freezer Door Assembly

Figure 4.7 Freezer Door Parts

Lever No. Part Name Quantity

1. Door freezer 1
2. Stopper ( M-shade ) 1
3. Screw tapping 1
4. Gasket freezer 1
5. Pocket freezer ( T-shade ) 1
6. Pocket freezer ( U-shade ) 1
 50

4.7 Refrigerator Door Assembly

Figure 4.8 Refrigerator Door Parts

Lever No. Part Name Quantity

1. Bushing refrigerator handle 1
2. Door refrigerator 1
3. Bushing refrigerator door 1
4. Stopper refrigerator door 1
5. Screw tapping 2
6. Gasket refrigerator door 1
7. Case egg 1
8. Pocket eggs 1
9. Pocket ( MULT ) 1
10. Pocket bottle 1
11. Pocket ( SM ) 1
4.8 Refrigerator Cub and Shelf

Figure 4.9 Refrigerator Cub and Shelf

 51

Lever No. Part Name Quantity

1. Case chilled 1
2. Shelf refrigerator 2
3. Cover case vegetable 1
4. Case vegetable 1

4.9 Control Box Assembly

Figure 4.10 Control Box Assembly Parts

Lever No. Part Name Quantity

1. Control box 1
2. Thermostat 1
3. Screw tapping 2
4. Box control hips 1
5. Switch Timer 1
6. Timer harness 1
7. R-shade 1
8. Knob thermostat 1
9. Socket lamp 1
10. Lamp 1
 52

4.10 Compressor Base Assembly

Figure 5.11 Compressor Base Assembly

Lever No. Part Name Quantity

1. Band relay 1
2. Washer special 4
3. Compressor ( 240V/50Hz ) 1
4. Switch relay 1
5. Absorbers compressor 4
6. Base compressor 1

4.11 Machine room view and Part list

Figure 5.12 Machine Room View and Parts List

Lever No. Part Name Quantity

 53

1. Cabinet 1
2. Case ( VAPORI ) 1
3. Absorber ( VAPORI ) 1
4. Switch relay 1
5. Relay cover 1
6. Pipe service 1
7. Clamp relay cover 1
8. Compressor 1
9. Wire earth 1
10. Base compressor 1
11. Absorber compressor 1
12. Cover cab 1
13. Vibration-roof gum 1
14. Pipe hot 1
15. Pipe suction 1
16. Base cab 1
17. Dryer 1
18. Pipe Connect ( Suction ) 1
19. Pipe Connect ( Deliver ) 1
20. Washer compressor 1
21. Foot adjust 1
22. Fixture compressor bolt 1
4.12 Trouble Shooting Chart
Compressor will not start
Possible Causes Symptoms Remedy
1. Power Failure No voltage on the socket Check power Supply
2. Blown Fuse No voltage on the socket Replace Fuse
3. Open line wire No resistance reading Connect open line
4. Defective Thermostat No resistance reading Replace Thermostat
5. Defective O.L.P No resistance reading Replace O.L.P
6. Open or Burn-out No resistance reading Replace compressor
compressor
7. Open relay No resistance reading Replace relay
 54

No Cooling while Compressor is Running

Possible Causes Symptoms Remedy
1. No refrigerant Low pressure reading Find any leak-repair
Low amperage Recharge refrigerant
Evaporator is warm
2. Loose compression Low pressure reading Replace compressor
Low amperage Recharge refrigerant
Low side and High side
have the same pressure
3. Oil in accumulator Warm evaporator Purge the system and remove
oil in the accumulator
Recharge the system
4. Restricted Strainer drier or Strainer-drier is cold Replace Strainer-drier
capillary tube No hizzing of refrigerant into Replace Capillary tube
the evaporator Replace refrigerant
5. Tripping compressor Compressor will run for a Check cause of tripping
while then stop, and run Correct the damage
again Replace compressor
6. Thermostat at set to lower Thremostat will trip for a Reset the thermostat
setting short period

Low Cooling
Possible Causes Symptoms Remedy
1. Lack or Refrigerant Low pressure Add refrigerant
Sweating evaporator
2. Moisturized Half of evaporator freezing Replace Strainer-Drier
while half is sweating Recharge refrigerant
3. Low setting of Thermostat Compressor will run for a Reset the Thermostat
short time
4. Excessive Food Load Low cooling Remove excess food
5. Frequent door opening Low cooling Minimize door opening
6. Loose door gasket Door will not close tightly Replace door gasket
7. Unit expose to heat Low cooling Re-install unit away from
heat
8. Defective Defrost timer The defrost heating is Replace Defrost timer
energizing as the compressor
is running
 55

Compressor Runs Continuously (24 hrs)

Possible Causes Symptoms Remedy
1. Defective Thermostat Thermostat contact is closed Replace Thermostat
2. Loose Door Gasket Door is not closing tightly Replace door gasket
3. Frequent door opening Low cooling Minimize door opening
4. Unit exposed to heat Low cooling Re-install the unit away from
heat

Compressor Tripping
Possible Causes Symptoms Remedy
1. High head pressure Over heating compressor Replace compressor
High ampere
2. Defective relay High ampere Replace relay
3. Shortage compressor High ampere Replace compressor
4. Stuck-up compressor High ampere Replace compressor
5. Low-voltage High ampere Check voltage reading
 56

Tutorial Sheet 4

1. Draw and Label the following Refrigerator Cycle Diagram.

2. Draw and Label the following Refrigerator Door Assembly.

3. List the possible causes, symptoms and remedy of the following troubles
(i) Compressor will not Start
(ii) No Cooling while Compressor is running
4. Write down the possible causes, symptoms and remedy in Low Cooling.

5. Write down the possible causes, symptoms and remedy in Compressor Runs Continuously
(24 hrs).

6. Write down the possible causes, symptoms and remedy in Compressor Tripping.
 REFERENCES

1. Refrigeration and Air Conditioning by CP Arora (3 rd Edition)

2. A Thermodynamics Approach to Refrigeration and Air Conditioning by A.l Khandwawala,
Govind Maheshwari, Sharad Chaudhary ( 2011)
3. Refrigearation and Air Conditioning I by Daw Thandar Aung (2002)
4. Air Conditioning Principles and Systems by Edward G. Pita (2nd Edition)
5. Refrigeration and Air Conditioning Repair and Troubleshooting Guide by Joy Job
Cabangon