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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