Installation, Start-Up, Adjustment and Maintenance Manual
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Flow Switch monitors the chilled water flow and shuts down the unit when the water flow stops or drops to
an insufficient level.
2.2 GAS FIRED CHILLER OPERATION CYCLE
The fluid used in the cooling cycle is a solution of water and ammonia (see Figure 2). Ammonia is the
refrigerant and water is the absorbing fluid. In the chiller’s generator, the ammonia-water solution is heated
to boiling by a burner 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 restrictor 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 restrictor.
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 restrictor.
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 solution 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.
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