chillers; a brief treatise

7/30/2019 Chillers; a brief treatise

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CHILLERS

Chillers consist of four main components:

1. The evaporator (the low temperature side of the system, i.e., the cooling

side)

2. The compressor

3. The condenser (the high temperature side of the system, i.e., the heat-

rejection side)

4. The expansion valve

TYPES OF CHILLERS

MECHANICAL COMPRESSOR CHILLERS

1. Reciprocating

2. Rotary screw

3. Centrifugal

4. Frictionless centrifugal

ABSORPTION CHILLERS

KEY COMPONENTS OF A MECHANICAL COMPRESSOR CHILLER

EVAPORATOR

Chillers produce chilled water in the evaporator where cold refrigerant

flows over the evaporator tube bundle. The refrigerant evaporates (changes into

vapour) as the heat is transferred from the water to the refrigerant. The chilled

water is then pumped, via the chilled-water distribution system to the buildings

air- handling units. The chilled water passes through coils in the air-handler to

remove heat from the air used to condition spaces throughout the building. The

warm water (warmed by the heat transferred from the building ventilation air)

returns to the evaporator and the cycle starts over.

Basically, there are two major categories of evaporators used in industrialrefrigeration practice. These are air coils and liquid chillers.

AIR-COILED EVAPORATORS

In the air coil, the refrigerant flows through the tubes and air passes over

the outside of the tubes. For effective heat transfer, fins are fastened to the

outside of the tubes and air flows between the fins.

LIQUID CHILLER EVAPORATORS


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The liquid-chilling evaporators in the figure below (fig. 1a & fig. 1b) are of

the shell-and-tube design, while fig. 2 is a plate-type chiller. In Fig. 1a the

refrigerant boils in the shell while the liquid flows through the tubes. In Fig. 1b

the roles of the tubes and shell are reversed. The plate-type evaporator in Fig. 2

is growing in market share and is an adaptation of the plate-type heat exchanger

used for many years in the food industry. Some of its popularity is attributable toits compactness and also that the refrigerant charge is less than in a shell-and-

tube evaporator. The reduced charge characteristic is attractive both when

ammonia and the new chlorine-free refrigerants are used. A low-charge ammonia

system is desirable for safety reasons, and a low-charge chlorine-free system

minimizes the cost of these expensive refrigerants.

Fig. 1 (a and b)
http://www.refrigers.com/content/view/31759/28/http://www.refrigers.com/content/view/31759/28/


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Fig. 2

COMPRESSOR

Vaporized refrigerant leaves the evaporator and travels to the compressor

where it is compressed mechanically, and changed into a high-pressure, high-

temperature vapour. Upon leaving the compressor, the refrigerant enters the

condenser side of the chiller.

CONDENSER

Inside the water-cooled condenser, hot refrigerant flows around the tubes

containing the condenser-loop water. The heat transfers to the water, causing

the refrigerant to condense into liquid form. The condenser water is pumped

from the condenser bundle to the cooling tower where heat is transferred from

the water to the atmosphere. The liquid refrigerant then travels to the expansion

valve.

EXPANSION VALVE


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The refrigerant flows into the evaporator through the expansion valve or

metering device. This valve controls the rate of cooling. Once through the valve,

the refrigerant expands to a lower pressure and a much lower temperature. It

flows around the evaporator tubes, absorbing the heat of the chilled water thats

been returned from the air handlers, completing the refrigeration cycle.

chillers; a brief treatise

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