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TRG-TRC016-EN 15
period one
Types of Water Chillers
notes
Absorption Water Chillers
So far, we have discussed water chillers that use the vapor-compression
refrigeration cycle. Absorption water chillers are a proven alternative to vapor-
compression chillers. The absorption refrigeration cycle uses heat energy as the
primary driving force. The heat may be supplied either in the form of steam or
hot water (indirect-fired), or by burning oil or natural gas (direct-fired).
There are two fundamental differences between the absorption refrigeration
cycle and the vapor-compression refrigeration cycle. The first is that the
compressor is replaced by an absorber, pump, and generator. The second is
that, in addition to the refrigerant, the absorption refrigeration cycle uses a
secondary fluid called the absorbent. The condenser, expansion device, and
evaporator sections, however, are similar.
Warm, high-pressure liquid refrigerant (D) passes through the expansion
device and enters the evaporator in the form of a cool, low-pressure mixture of
liquid and vapor (A). Heat is transferred from the relatively-warm system water
to the refrigerant, causing the liquid refrigerant to boil. Using an analogy of the
vapor-compression cycle, the absorber acts like the suction side of the
compressor—it draws in the refrigerant vapor (B) to mix with the absorbent.
The pump acts like the compression process itself—it pushes the mixture of
refrigerant and absorbent up to the high-pressure side of the system. The
generator acts like the discharge of the compressor—it delivers the refrigerant
vapor (C) to the rest of the system.
The refrigerant vapor (C) leaving the generator enters the condenser, where
heat is transferred to cooling-tower water at a lower temperature, causing the
refrigerant vapor to condense into a liquid. This high-pressure liquid refrigerant
(D) then flows to the expansion device, which creates a pressure drop that
reduces the pressure of the refrigerant to that of the evaporator, repeating
the cycle.
The absorption refrigeration cycle is discussed in more detail in the Absorption
Water Chillers Air Conditioning Clinic.
Absorption Refrigeration Cycle
pump
pump
expansion
expansion
device
device
absorb heat
absorb heat
reject heat
reject heat
heat energy in
heat energy in
reject heat
reject heat
evaporator
evaporator
condenser
condenser
absorber
absorber
generator
generator
A
B
C
D
Figure 18