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TRG-TRC005-EN 11
period two
Condensers
notes
A reduction in condensing pressure lessens the power required to compress
the refrigerant. Unfortunately, if the condensing pressure falls too low, the
expansion valve may not be able to produce the flow of liquid refrigerant
needed to satisfy the demand at the evaporator. In some systems, as the
condensing pressure drops, the compressor suction pressure also drops,
resulting in evaporator frosting and possible compressor shutdown due to a
low-pressure safety device.
While it is not essential to control condensing pressure to a constant value,
provisions should be made to control it within acceptable limits.
One common method of controlling the capacity of a water-cooled condenser is
to vary the rate at which water flows through the condenser.
For example, assume a water-cooled condenser is piped to a municipal water
system. To control the capacity of the condenser, a flow-regulating valve is
installed on the leaving-water side of the condenser. As the load on the system
decreases, the regulating valve senses the lowering condensing pressure. The
valve reduces the flow rate of the water until the heat-rejection rate of the
condenser balances the system load at an acceptable pressure and
temperature.
Condensing Temperature Control
condenser
condenser
water pump
water pump
flow-regulating
flow-regulating
valve
valve
condenser
condenser
Figure 17