A chiller is a machine that removes heat from a liquid via a vapour compression and vapour absorption cycle. This liquid can then be circulated through a heat exchanger to cool equipment or another process steam. As a necessary by-product, refrigeration creates waste heat that must be exhausted to ambience or for greater efficiency, recovered for heating purposes Chilled water is used to cool and dehumidify air in mid-to-large-size commercial, industrial and institutional facilities. A water chiller can be water cooled, air cooled or evaporative cooled
Water-cooled chiller systems have a cooling tower, thus they feature higher efficiency than air-cooled chillers. Water-cooled chillers are more efficient because they condense depending on the ambient temperature bulb temperature, which is lower than the ambient dry bulb temperature. The lower a chiller condenses, the more efficient it is.
Where aesthetics and environmental conditions or water access restrictions exist, the air-cooled chiller may be applied. Both air-cooled and water-cooled chillers depend on an air stream as a means of heat transfer.
The difference is that the water-cooled chillers or rather the cooling towers use a humid air stream (ambient air stream + water spray) while the air-cooled chillers use a current of ambient air. Normally water-cooled chillers are cheaper and more efficient, with the disadvantage of high water consumption.
No big difference is found in the water-cooled chiller and air-cooled chiller except the material used for cooling. Rest all components such as evaporator, condenser, compressor, and an expansion valve are same.
The cycle begins in the evaporator where a liquid refrigerant flows over the evaporator tube bundle and evaporates, absorbing heat from the chilled water circulating through the bundle. The refrigerant vapor is drawn out of the evaporator by the compressor. The compressor then “pumps” the refrigerant vapor to the condenser raising its pressure and temperature. The refrigerant condenses on or in the condenser tubes, giving up its heat to the cooling water (or air). The high pressure liquid refrigerant from the condenser then passes through the expansion device that reduces the refrigerant pressure and temperature as it enters the evaporator. The refrigerant again flows over the chilled water coils absorbing more heat and completing the cycle.
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