Handbook of air conditioning and refrigeration / Shan K

14.24 CHAPTER FOURTEEN
absorber and condenser of the no. 2 absorption heat pump, and from 152 to 160.5°F (66.7 to
71.4°C) in the absorber and condenser of the no. 1 absorption heat pump. In the evaporator, heat
was extracted from the low-temperature heat source, the flue gas cooling water, which entered the
absorption heat pump at a temperature of 97.7°F (36.5°C) and left at a temperature of 75.2°F
(24°C). The high-temperature heat source, steam, was supplied at 320°F (160°C) at a flow rate of
66,000 lb/h (29,940 kg/h) from the incineration plant. The average COP hp for this series-connected
absorption heat pump from July 15 through August 31, 1987, was 1.61.
14.9 ABSORPTION HEAT TRANSFORMER
System Description
Operating Characteristics
Large amounts of low-temperature waste heat are released daily from many industrial plants.
Absorption heat transformers are systems that operate in a cycle opposite to that of absorption
chillers, to boost the temperature of input waste heat 40 to 100°F (22 to 56°C) higher for industrial
applications.
Most absorption heat transformers today are single-stage systems using lithium bromide as the
working fluid for industries in Japan and Europe. Two-stage absorption heat transformers for
greater temperature boosting and use with working fluids other than LiBr are being developed.
An absorption heat transformer consists of an evaporator, absorber, generator, condenser, heat
exchanger, solution pump, refrigerant pump, piping, and accessories. Figure 14.8 shows the
schematics and the absorption cycle on the equilibrium chart of a typical single-stage absorption
heat transformer using LiBr as the absorbent. In a heat transformer, because the heat is supplied
from the waste heat fluid stream entering at low temperature T 1 and leaving at lower temperature T 2,
water is vaporized from the evaporator and extracted by the absorbent sprayed in the absorber at
point 11. Heat of absorption is then released from the absorbent to the hot water stream entering at
a temperature T 3 and raised to a temperature T 4. After absorbing the water vapor, the diluted
solution at point 12 enters the heat exchanger, which is also called the recuperator. Diluted solution
leaves the heat exchanger at a lower temperature, flows through a regulating valve, and enters the
generator, or desorber, at point 13. Because of the heat input from the waste heat fluid streams, water
vapor boils off from the diluted solution and is condensed in the condenser. The concentrated
solution leaves the generator at point 14 and is pumped to a higher pressure equal to the pressure in
the absorber. Liquid water in the condenser is pumped to the evaporator for evaporation again.
The absorption heat transformer operates at two pressure levels: high pressure, including the evaporator
and absorber; and low pressure, including the generator and condenser. There are three temperature
levels of input and output fluid streams:
● The fluid stream carrying the heat output from the absorber is at the highest temperature level.
● The heat source (the waste heat input to the evaporator and generator) is at the intermediate temperature
level.
● The cooling water in the condenser is at the lowest temperature level.
The purpose of an absorption heat transformer is to boost the temperature of the input waste heat
fluid stream, and the function of an absorption heat pump is to attain a higher COP from the lowertemperature
heat source.