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1.5. Heat driven cooling
3 → 4: The refrigerant is evaporated in the evaporator (EVAP).
Heat is transferred at a low temperature from an external circuit of
water or a brine which is thereby being chilled.
4 → 5: The refrigerant is absorbed by the strong absorption
solution (rich in absorption medium) entering at point 12. This
process is exothermic due to both condensing of refrigerant and
mixing of refrigerant and solution. The heat is removed by an
external cooling circuit.
5 → 6: The liquid weak solution (poor in absorption media) is
pressurized by a pump in order to reach the high pressure.
6 → 7: The solution is preheated in the solution heat exchanger.
7 → 9: The weak solution is heated by an external high temperature
heat source which makes the refrigerant boil of.
9 → 11: The strong solution is sent through the solution heat
exchanger and heat is recovered by the weak solution.
11 → 12: The high pressure of the strong solution is reduced to the
low pressure by an expansion valve before it enters the absorber.
In cycles using the ammonia-water solution (or similar solution) it
is necessary to install a rectifier (”water separator”) after the desorber
(DES in figure 1.2) to ensure that only refrigerant (ammonia) is sent to
the condenser ([18]). If the refrigerant is not free of absorption medium,
it will decrease the performance of the system.
Cycle configurations
The performance of the single stage cycle 10 described previously is quite
limited (COP is in the range of 0,6 to 0,8). To increase the performance,
various configurations have been developed. In the following some of
these alternative cycles of ammonia-water and water-lithium bromide
are listed and their respective COP’s are indicated to compare the
performance of the different configurations:
10 In the literature the phrase single effect cycle is often for describing the same thing.
11