Installation, Start-Up, Adjustment and Maintenance Manual
7
2.2 USED OIL AND GAS FIRED CHILLER OPERATION CYCLE
DESCRIPTION OF THE ABSORPTION REFRIGERANT CYCLE
The fluid used in the cooling cycle is a solution of water and ammonia (see Figure 1). Ammonia is the
refrigerant
and water is the absorbing fluid. In the chiller’s generator, the ammonia-water solution is
heated to boiling producing both a vapor with a strong concentration of ammonia and a liquid solution
with a low concentration of ammonia. Liquid solution with a low concentration of ammonia is called a
"weak solution".
The ammonia vapor passes into the rectifier, which separates the water from the vapor. The hot and
pressurized ammonia vapor exiting the rectifier enters the condenser where it is cooled and changed
to a liquid.
The liquid ammonia is then brought to a lower pressure by means of a restricter and further cooled in
a “tube-in-tube” refrigerant heat exchanger. Finally, the liquid ammonia is reduced to a pressure of 39
to 60 psig and a temperature lower than 37°F by a second restricter.
Under this low pressure and temperature condition, liquid ammonia enters the evaporator where the
ammonia evaporates due to heat being removed from water returning from the user's required cooling
application (thermal blowers, fan-coils, etc.) within the chilled water system.
The cold, low-pressure ammonia vapor exiting the evaporator exchanges heat with the liquid ammonia
coming from the condenser in the refrigerant heat exchanger. The ammonia vapor then enters the
“solution cooled absorber” where it comes into contact with "weak solution" from the generator that
has been brought to a low pressure by means of a restricter.
Inside the “solution cooled absorber” the absorption process starts, i.e. the dilution of ammonia vapor
into the "weak solution". The absorption of ammonia vapor is an exothermic process. (i.e. heat is
produced) To have the vapor completely absorbed by the solution, the solution exiting the “solution
cooled absorber” must be further cooled in a portion of the condenser/absorber coils.
Once the absorption process is complete, the liquid solution contains a high concentration of
ammonia, also called "strong solution". A hydraulically driven, diaphragm pump pumps the “strong
solution” to the generator at high pressure.
As the “strong solution” is pumped to the generator, it passes through the coil of the rectifier and the
solution cooled absorber (the GAX section) where it is preheated before entering the generator. The
cycle then starts over.
