period one
Types of Water Chillers
notes
Absorption Refrigeration Cycle
reject heat
heat energyin
DC
condenser | generator | |
expansion | pump | |
device | | |
evaporator | absorber | |
A | B | |
| |
absorbheat | reject heat | Figure 18 |
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.
