Source cooling equipment includes refrigeration compressors of reciprocating, centrifugal, and screw types; absorption chillers using steam, hot water, or direct fuel firing; water chiller heat exchangers; condensers cooled by air, water, and evaporation; cooling towers; and evaporative coolers, including spray, slinger, and drip types.

Self-contained package AHUs typically use direct-expansion cooling with reciprocating or rotary compressors. Other AHUs may use direct expansion, chilled water, or brine cooling, with the cooling medium provided by a separate, centralized, refrigeration system.

 Evaporative cooling is used primarily in climates with low design ambient wet-bulb temperatures, although it may be used in almost any climate to achieve some cooling. Evaporative cooler efficiencies are highest for the spray type and lowest for the drip type.

Centrifugal and screw-type compressors and absorption refrigeration are used almost entirely in large central station water or brine chillers. Absorption refrigeration may be uneconomical unless there is an adequate source of waste heat or solar energy.

Air-cooled condensers are less costly to purchase and maintain than cooling towers or evaporative condensers, but they result in higher peak condensing temperatures at design conditions and may result in lower overall efficiency in the cooling system.

The selection of the source cooling equipment is influenced primarily by the selection of the AHU equipment and systems. Often both are selected at the same time.

The use of individual room units does not preclude the use of central-station chillers; this combination may be preferable in many situations. For off-peak cooling with storage, a central chilling plant is an essential item.

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1 comment:

Laura Bush said...

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