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14 TRG-TRC005-EN
notes
period two
Condensers
A common method of controlling the capacity of an air-cooled condenser is to
vary the airflow across the condenser coil. The heat-rejection rate of a multiple-
fan condenser is often controlled by cycling fans on and off to maintain
acceptable condensing pressures. Alternatively, the airflow across the coil can
be varied by using a damper or a variable-speed drive on one or more of the
fans.
In this example, a damper has been added to one of the two condenser fans.
Capacity control is accomplished by cycling fan B on and off while varying the
airflow of fan A by modulating the damper. Both the damper and the cycled fan
are controlled by condensing pressure. As the heat-rejection requirement
increases, fan A continues to open its damper farther to increase its airflow.
When fan A reaches full airflow, fan B turns on and fan A modulates its damper
to continue to match the desired heat rejection rate.
Another, less common method of controlling the capacity of an air-cooled
Air-Cooled Condenser Control
heat rejection capacity
heat rejection capacity
condenser airflow
condenser airflow
fan
fan A
fan
fan B
fan
fan A
damper
damper
A
B
Figure 21
Condenser Flooding Control
evaporator
evaporator
compressor
compressor
liquid receiver
liquid receiver
B
A
C
condenser
condenser
expansion
expansion
valve
valve
discharge line
discharge line
Figure 22