Building Services Engineering 5th Edition Handbook

Ventilation and air conditioning 155
Condenser
2
Condenser
cooling water
to cooling
tower
Heat
input
1
6
Generator
7
Heat
exchanger
Evaporator
3
Chilled
water
4
8
9
Cooling
water to
cooling
tower
Absorber 5
5.19 Two-drum absorption refrigeration cycle.
is pumped back into the higher-pressure generator drum to complete the cycle. This pump is the
only moving part of some systems. Concentrated salt solution (6) is passed down to the absorber
via a heat exchanger and pressure-reducing valve to replace the salt removed. The production of
chilled water is equivalent to about half the heat input to the generator.
The gas domestic refrigerator works on an absorption system using liquid evaporation to
provide the cooling effect. Figure 5.20 shows the features of modern equipment. A solution of
ammonia in water is heated in the boiler (A) by a small gas flame. This is the only energy input.
Ammonia gas is driven off the solution and then condensed to a liquid in the air-cooled condenser
(B) outside the refrigerator cabinet. The liquid ammonia then passes, with some hydrogen, into
the evaporator (C) inside the refrigerator cabinet. This is the ice box. The ammonia completely
evaporates while absorbing the heat from the cabinet. The two gases are then led into the
absorber (D), where the ammonia is absorbed by a weak solution trickling down the absorber.
The strong ammonia solution produced is then driven back into the boiler, while the hydrogen
gas, which is not absorbed, passes to the evaporator. The weak solution trickling down the
absorber is provided from the boiler. Both types of absorption refrigerator provide cooling from
a source of heat, they have few or no moving parts and they only require low-power pumps.
This makes the cycle suitable for solar power input. The equipment is vibrationless and very
quiet in operation.