2. Introduction
How does
it work?
High Temperature Reservoir
Low Temperature Reservoir
R Work Input
Heat Absorbed
Heat Rejected
By: Mudit M. Saxena, Dept. of Mech. Engg.
3. 3
Coefficient of Performance
(CoP)
• Coefficient of Performance (CoP) is very
important in determining a system's overall
efficiency.
• It is defined as refrigeration capacity in kW
divided by the energy input in kW. While
CoP is a very simple measure, like the kW.
By: Mudit M. Saxena, Dept. of Mech. Engg.
4. 4
Units of refrigeration
• The units of refrigeration are always a unit
of power. Domestic and commercial
refrigerators may be rated in kJ/s, or Btu/h
of cooling.
• For commercial and industrial refrigeration
systems most of the world uses the kilowatt
(kW) as the basic unit refrigeration.
By: Mudit M. Saxena, Dept. of Mech. Engg.
5. 5
Ton of Refrigeration (TR).
One Ton of Refrigeration was defined as the
energy removal rate that will freeze one ton of
water at 0 °C (32 °F) in one day(24 Hrs).
One Ton’s value as historically defined is
approximately 11,958 BTU/hr (3.505 kW) has
been redefined to be exactly 12,000 BTU/hr
(3.517 kW).
By: Mudit M. Saxena, Dept. of Mech. Engg.
6. 6
Introduction
AC options / combinations:
AC Systems
• Air Conditioning (for comfort / machine)
• Split air conditioners
• Fan coil units in a larger system
• Air handling units in a larger system
By: Mudit M. Saxena, Dept. of Mech. Engg.
7. 7
Types of Refrigeration
• Vapour Compression
Refrigeration (VCR): uses
mechanical energy
• Vapour Absorption Refrigeration
(VAR): uses thermal energy
Refrigeration systems
By: Mudit M. Saxena, Dept. of Mech. Engg.
8. 8
Type of Refrigeration
Vapour Compression Refrigeration
• Highly compressed fluids tend to get
colder when allowed to expand
• If pressure high enough
• Compressed air hotter than source
of cooling
• Expanded gas cooler than desired
cold temperature
By: Mudit M. Saxena, Dept. of Mech. Engg.
9. 9
VAPOUR COMPRESSION REFRIGERATION
CYCLE ( T-S diagram )
1-2 Isentropic
compression
2-3 Constant pressure
heat rejection in the
condenser
3-4 Throttling in an
expansion valve
4-1 Constant pressure
heat addition in the
evaporator
By: Mudit M. Saxena, Dept. of Mech. Engg.
10. 10
VAPOUR COMPRESSION REFRIGERATION
CYCLE ( p-h diagram )
1-2 Isentropic compression
2-3 Constant pressure heat
rejection in the condenser
3-4 Throttling in an
expansion valve
4-1 Constant pressure heat
addition in the evaporator
By: Mudit M. Saxena, Dept. of Mech. Engg.
11. By: Mudit M. Saxena, Dept. of Mech
. Engg.
11
Typical Refrigeration Cycle
13. 13
Vapour Compression Refrigeration
Two advantages
• Lot of heat can be removed (lot of
thermal energy to change liquid to
vapour)
• Heat transfer rate remains high
(temperature of working fluid much
lower than what is being cooled)
By: Mudit M. Saxena, Dept. of Mech. Engg.
15. 15
Refrigeration cycle
Low pressure liquid
refrigerant in evaporator
absorbs heat and changes
to a gas
Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1 2
3
4
By: Mudit M. Saxena, Dept. of Mech. Engg.
Vapour Compression Refrigeration
16. 16
Vapour Compression Refrigeration
Refrigeration cycle
The superheated vapour
enters the compressor
where its pressure is
raised
Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1 2
3
4
By: Mudit M. Saxena, Dept. of Mech. Engg.
17. 17
Vapour Compression Refrigeration
Refrigeration cycle
The high pressure
superheated gas is cooled
in several stages in the
condenser
Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1 2
3
4
By: Mudit M. Saxena, Dept. of Mech. Engg.
18. 18
Vapour Compression Refrigeration
Refrigeration cycle
Liquid passes through expansion
device, which reduces its pressure
and controls the flow into the
evaporator
Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1 2
3
4
By: Mudit M. Saxena, Dept. of Mech. Engg.
19. 19
Vapour Compression Refrigeration
Type of refrigerant
• Refrigerant determined by the
required cooling temperature
• Chlorinated fluorocarbons (CFCs) or
freons: R-11, R-12, R-21, R-22 and R-
502
By: Mudit M. Saxena, Dept. of Mech. Engg.
20. 20
Vapour Compression Refrigeration
Choice of compressor, design of
condenser, evaporator determined by
• Refrigerant
• Required cooling
• Load
• Ease of maintenance
• Physical space requirements
• Availability of utilities (water, power)
By: Mudit M. Saxena, Dept. of Mech. Engg.
24. 24
A thermostatic expansion valve system,
In a thermostatic expansion valve system,
the components necessary for system
operation are:
the condenser, the evaporator, the
compressor, the receiver drier, the
thermostatic expansion valve, connecting
pipes and hoses, a thermostat, blower fans
and pressure switches.
The thermostatic expansion valve, also
called a TX valve, is located at the entry to
the evaporator and provides a throttling or
restricting function to control the quantity
of refrigerant entering the evaporator. At
the same time it must provide for complete
vaporization of all the liquid refrigerant
which enters the evaporator.
The system is charged with refrigerant and
a quantity of lubricating oil which
circulates with the refrigerant at all times.
By: Mudit M. Saxena, Dept. of Mech. Engg.
27. 27
SPLIT – AIR CONDITIONER SCHAMATIC
By: Mudit M. Saxena, Dept. of Mech. Engg.
28. 28
It uses heat energy instead of mechanical work. It eliminates
compressor.
The vapours are absorbed in the liquid which are pumped into
generator where heat energy is supplied to generate vapours of
high pressure.
Pump needs a small amount of work for circulating the liquid.
Vapour Absorption Refrigeration
29. Vapour Absorption Refrigeration
• Two widely used absorbent and
refrigeration pairs are:
(1) Ammonia Water system
Ammonia – refrigerant;
Water – Absorbent
(2) Water lithium bromide system –
Water – Refrigerant ;
Lithium bromide- absorbent
• The function of compressor in vapour
compression is replaced by absorber,
generator, throttle valve and pump.
• The remaining component namely
components condenser, throttle valve,
and evaporator are same.
29
30. 30
Working:
Ammonia water solution is kept in the generator,
where heat energy is supplied from an external
source. Ammonia vapours are generated at point
1 and flow through the pipe to the condenser.
These vapours get codensed and reject heat
externally and flow through the throttle valve
(Point 2).
Liquid ammonia is throttled through the
expansion valve where both temperature and
pressure fall.(Point 3)
Liquid now enters the evaporator . Here
ammonia evaporates by absorbing latent heat of
evaporation to produce refrigeration effect.
After absorbing heat the liquid converts into
vapours and enters the absorber. (Point 4) .In the
absorber weak solution (Ammonia+Water) also
enters through throttling valve point (8).
Vapour Absorption Refrigeration
31. 31
It absorbs ammonia to become strong solution
which is pumped ( Point 5) with the help of a
pump to the generator (Point 6). Thus cycle is
completed.
The pump work is considered negligible in
comparison to heat supplied in the generator
and refrigeration effect is obtained in the
evaporator.
The coefficient of performance ( COP ) is
expressed as the ratio of refrigeration effect ( in
evaporator ) to heat supplied ( in generator ).
The value of COP is only 20 to 30 % of the
COP of vapour compression system at the same
refrigeration temperature.
Vapour Absorption Refrigeration
Editor's Notes
#1:TO THE TRAINER
This PowerPoint presentation can be used to train people about the basics of refrigeration and air condonditioning. The information on the slides is the minimum information that should be explained. The trainer notes for each slide provide more detailed information, but it is up to the trainer to decide if and how much of this information is presented also.
Additional materials that can be used for the training session are available on www.energyefficiencyasia.org under “Energy Equipment” and include:
Textbook chapter on this energy equipment that forms the basis of this PowerPoint presentation but has more detailed information
Quiz – ten multiple choice questions that trainees can answer after the training session
Option checklist – a list of the most important options to improve energy efficiency of this equipment
#2:Refrigeration and air conditioning is used to cool products or a building environment.
The refrigeration or air conditioning system (R) transfers heat from a cooler low-energy reservoir to a warmer high-energy reservoir
#6:Depending on applications, there are several options / combinations of air conditioning, which are available for use:
Air conditioning (for space or machines)
Split air conditioners
Fan coil units in a larger system
Air handling units in a larger system
#7:The two principle types of refrigeration plants found in industrial use are: Vapour compression refrigeration (VCR) and vapour absorption refrigeration (VAR). VCR uses mechanical energy as the driving force for refrigeration, while VAR uses thermal energy as the driving force for refrigeration.
#8:Compression refrigeration cycles take advantage of the fact that highly compressed fluids at a certain temperature tend to get colder when they are allowed to expand.
If the pressure change is high enough, then the compressed gas will be hotter than our source of cooling (outside air, for instance) and the expanded gas will be cooler than our desired cold temperature. In this case, fluid is used to cool a low temperature environment and reject the heat to a high temperature environment.
#13:Vapour compression refrigeration cycles have two advantages.
First, a large amount of thermal energy is required to change a liquid to a vapor, and therefore a lot of heat can be removed from the air-conditioned space.
Second, the isothermal nature of the vaporization allows extraction of heat without raising the temperature of the working fluid to the temperature of whatever is being cooled. This means that the heat transfer rate remains high, because the closer the working fluid temperature approaches that of the surroundings, the lower the rate of heat transfer.
#14:The refrigeration cycle is shown in the Figure and can be broken down into the following stages (note to the trainer: the next slides will explain what is happening between 1 to 4)
#15:The refrigeration cycle is shown in the Figure and can be broken down into the following stages (note to the trainer: the numbers 1-4 are shown in the figure):
1 – 2. Low-pressure liquid refrigerant in the evaporator absorbs heat from its surroundings, usually air, water or some other process liquid. During this process it changes its state from a liquid to a gas, and at the evaporator exit is slightly superheated.
#16:The refrigeration cycle is shown in the Figure and can be broken down into the following stages (note to the trainer: the numbers 1-4 are shown in the figure):
2 – 3. The superheated vapour enters the compressor where its pressure is raised. The temperature will also increase, because a proportion of the energy put into the compression process is transferred to the refrigerant.
#17:The refrigeration cycle is shown in the Figure and can be broken down into the following stages (note to the trainer: the numbers 1-4 are shown in the figure):
3 – 4. The high pressure superheated gas passes from the compressor into the condenser. The initial part of the cooling process (3-3a) de-superheats the gas before it is then turned back into liquid (3a-3b). The cooling for this process is usually achieved by using air or water. A further reduction in temperature happens in the pipe work and liquid receiver (3b - 4), so that the refrigerant liquid is sub-cooled as it enters the expansion device
#18:The refrigeration cycle is shown in the Figure and can be broken down into the following stages (note to the trainer: the numbers 1-4 are shown in the figure):
1 – 2. Low-pressure liquid refrigerant in the evaporator absorbs heat from its surroundings, usually air, water or some other process liquid. During this process it changes its state from a liquid to a gas, and at the evaporator exit is slightly superheated.
2 – 3. The superheated vapour enters the compressor where its pressure is raised. The temperature will also increase, because a proportion of the energy put into the compression process is transferred to the refrigerant.
3 – 4. The high pressure superheated gas passes from the compressor into the condenser. The initial part of the cooling process (3-3a) de-superheats the gas before it is then turned back into liquid (3a-3b). The cooling for this process is usually achieved by using air or water. A further reduction in temperature happens in the pipe work and liquid receiver (3b - 4), so that the refrigerant liquid is sub-cooled as it enters the expansion device.CondenserEvaporatorHigh Pressure SideLow Pressure SideCompressorExpansion Device1234
4 - 1 The high-pressure sub-cooled liquid passes through the expansion device, which both reduces its pressure and controls the flow into the evaporator
#19:A variety of refrigerants are used in vapor compression systems. The choice of fluid is determined largely by the cooling temperature required.
Commonly used refrigerants are in the family of chlorinated fluorocarbons, CFCs, also known as freons: R-11, R-12, R-21, R-22 and R-502.
#20:The choice of refrigerant and the required cooling temperature and load determine the choice of compressor, as well as the design of the condenser, evaporator, and other auxiliaries.
Additional factors such as ease of maintenance, physical space requirements and availability of utilities for auxiliaries (water, power, etc.) also influence component selection.
