HVAC PRIME SOURCE, LLC

CHILLERS & DIRECT EXPANSION (DX) UNITS.

General

Chillers and DX units are the two main type of equipment used for air conditioning. Chillers provide cooling of the chilled water which is then used in the air cooling coils for air conditioning, while DX units provide cooling by direct expansion of the refrigerant in the air cooling coils. The air cooling coil in DX units and the chilled water heat exchanger in chillers are also called an "Evaporator" since evaporations of the liquid refrigerant occurs in these components.

In general DX units are used for relatively small capacity systems and chillers are used for relatively large capacity system. Typically a DX system is not used for systems larger than 100 ton capacity. Further variations of applications are as follows.

Chillers are available in the following major categories, based on the type of compressor and size of the application. Typically chillers are package units on one skid, with the water piping system being external to the unit. The package unit includes the compressor, condenser, evaporator and associated components.

• Centrifugal compressor chillers (used for medium to large capacity applications)
• Screw compressor chillers (used for medium capacity applications)
• Reciprocating compressor chillers (used for small to medium capacity applications)
• Scroll compressor chillers (used for small to medium capacity applications)

DX Units are available in following major categories, based on the type of the compressor and packaged or split design:

• Reciprocating or scroll compressor package units (condenser, compressor & evaporator are on the same skid).
• Reciprocating or scroll compressor split systems (condenser, compressor, evaporator are located at separate locations - many systems have the condenser + compressor on the same skid as condensing unit, and the evaporator is located separately)

The condenser for both DX units and chillers can be air cooled or water cooled for relatively smaller sizes. For the larger units the condenser is typically water cooled.

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Last modified:11/16/2008