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Types: Chillers

Chillers 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.

Engine-driven 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.

Vapor compression 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.

Mechanical 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.

Engine-driven 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.

Further, engine 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.

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