period three
Capacity Control
notes
its way into the chiller through any available path. As explained earlier, the pressure and temperature inside the evaporator are determined by the concentration and temperature of the solution in the absorber. If air leaks into the chiller, however, the evaporator pressure increases because a portion of the volume inside the
Sensing the increasing temperature of the chilled water leaving the evaporator, the chiller control system attempts to overcome the condition by increasing the amount of solution delivered to the generator and by increasing the amount of heat input to the generator. This causes more refrigerant to be boiled off in the generator and results in a more concentrated solution being delivered to the heat exchanger. Under higher load conditions, it is possible to increase this solution concentration to the point where crystallization occurs in the heat exchanger.
In most modern absorption chillers,
▲
◆Decreases temperature of dilute solution traveling to generator
◆Results in lower temperature of concentrated solution returning to absorber
◆Causes concentrated solution inside heat exchanger to crystallize
Figure 48
Cooling water that is too cold, combined with a high load on the chiller, is another possible cause of crystallization. Colder cooling water causes the temperature of the dilute solution travelling from the absorber to the generator to drop. This cool dilute solution entering the heat exchanger absorbs a greater amount of heat from the concentrated solution and, therefore, results in a lower temperature of concentrated solution leaving the heat exchanger. If the temperature drops low enough, crystallization of the concentrated solution can occur.
In the past, absorption chillers were designed to operate with constant- temperature cooling water. With these chillers, a sudden drop in the temperature of the cooling water could result in crystallization. The microelectronic controls for many modern absorption chillers are designed to
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