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Refrigeration,
Heat pumps andAir Conditioning
Lecture 3
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Efficiency of a cooling system
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Coefficient of Performance
(COP)
COP is dimensionless.
The higher the COP, the more efficient
the heat pump.
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COMPRESSION COOLING
Vapor
Condenser
Expansion
Compression
Evaporator
Vapor
LiquidLiquid +
Vapor
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Required cooling temperature largely determines the choice of
refrigerant.
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.
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ABSORPTION COOLING
A heat source is used to provide energy for the cooling
process.
Evaporating liquid used is typically water .
To increase the rate of evaporation, a hygroscopic (water
absorbing) solution is introduced in the absorbing
chamber. Usually in commercial applications it is lithium
bromide (LiBr) salt solution.
As the heat source steam or any waste heat stream can
be used.
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Evaporator
Absorber
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High pressure generator
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Condenser
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Comparison
Compression Cooling
Uses electricity or
mechanical energy
Relatively high COP Generate a high level of
noise
Risk of environmental
pollution
Absorption Cooling
Uses steam or waste heat
stream.
Relatively low COP Relatively less noisy.
Environment friendly
Direct fired units can reach
for higher efficiencies. Can be coupled with CHP
systems to make use of the
waste heat streams.
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EvaporativeCooling
Air in contact with waterto cool it closeto wet
bulbtemperature
Advantage:efficient cooling atlow cost
Disadvantage:air isrich inmoisture
ColdAir
HotAir
Sprinkling
Water
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Maximum or Carnot Efficiency
COP = TMin / ( T Max T Min )
TMin =Minimum Temperature
TMax =Maximum Temperature