are used to cool a stream of chilled water, which in turn, is used in manufacturing
to cool processes or sent to air coils to cool and dehumidify the air being delivered
to the zones of a building. Smaller air-conditioning units, such as split systems
and packaged rooftop units, typically do not employ chilled-water streams or cooling
water streams, but rather use direct expansion (DX) refrigerant air coils to both
directly remove heat from the condenser and to cool and dehumidifythe conditioned
air stream with the evaporator.
cooling systems employ a conventional vapor compression cycle. The main components
of a vapor compression system are the compressor, condenser, expansion valve,
and evaporator as shown in the following diagram. The four main steps in this
cycle are also shown on the following page.
equipment typically uses one of three different types of compressors: reciprocating,
screw or centrifugal. Reciprocating compressors are typically used for smaller
applications of 200 tons or less. Screw compressors, such as the single screw
or twin screw, are used for applications ranging from 100 to 1,250 tons. Centrifugal
compressors, which can be single or multiple stage, are used for applications
ranging from 100 to 10,000 tons.
chillers can be driven by any type of motor or engine, depending upon the compressor
design. Industrial-grade or marine-derivative engines are typically used because
of their long life and reduced maintenance intervals.
systems are the preferred technology in many cases, spurred on by a number of
benefits. In addition to their cost advantage over electricity, engine-driven
units have variable speed capability, making them more efficient than electric
units to operate partial loads. This is particularly significant to the air conditioning
market, which commonly operates at partial loads.
jacket water and exhaust gas can be recovered and used to heat boiler feedwater,
tank heating, regeneration of desiccants and for domestic hot water, reheating,
swimming pool heating and other HVAC requirements. Using waste heat increases
engine operating efficiency, which reduces total energy needs.