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Demand continues to mount for
improved comfort conditioning combined with lower operating
costs. New architectural designs have created real
problems for contractors and engineers to maintain humidity
control at reduced loads, and to control load variations.
Refrigeration and air conditioning systems are usually designed
to provide a given capacity at maximum conditions. These operate
with little fluctuation throughout a narrow load range.
However, only the larger size machines make any provisions for
operation at reduced capacity. In some systems, integral
cylinder unloading, the installation of a gas engine drive with
variable speed control, or even multiple smaller systems,
provide a logical solution.
Many manufacturers now
recommend use of a modulating control valve to provide a metered
flow of compressor discharge gas to the system low side, in a
proportion that will balance the system capacity to the load
demand. This is commonly known as the hot gas bypass
method. It permits full modulation of capacity on all
types of reciprocating compressors, and extends capacity
reduction below that last step of cylinder unloading.
Basically, the system must
provide a means of bypassing high-pressure refrigerant to the
system low-pressure side, in order to maintain operation at a
given minimum suction pressure. Proper bypass control can
be a accomplished by a modulating type pressure regulator, which
opens on a decrease in valve outlet pressure.
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