CHILLERS AND AIR COOLING PACKAGES
These are true packaged units in the sense that all the parts of the refrigeration system and its controls are factory assembled and tested in the complete state. There are four configurations:
• Air cooling, air-cooled
• Air cooling, water-cooled
• Liquid cooling, air-cooled
• Liquid cooling, water-cooled
Air cooling packages are limited by the volume of cooled air that needs to be in close proximity to the machinery. Examples of fully packaged air coolers are room air conditioners of the integral ‘)hrough the wall’ type (Chapter 25) and refrigerated vehicle units (Chapter 17).
Liquid cooling packages, frequently termed ‘ chillers’, are self-contained systems and may be either air-cooled or water-cooled (Figures 13.7 and 13.8). Because chilled water is a highly flexible and efficient means of distributing cooling in many types of building, the range of chillers available on the market is very large. They can be found with compressors of all types: reciprocating, scroll, screw and centrifugal together with heat exchangers of the shell and tube type or plate heat exchangers. Two refrigerant circuits are commonly used because this gives more capacity flexibility and offers some redundancy. Air conditioning is the main application, but they are also used for process cooling where the range of temperatures can be extended downward by use of brine instead of water. Water-cooled chillers are most frequently linked to cooling towers and this improves the chillers’ overall thermodynamic effectiveness as compared to air-cooled chillers because heat rejection is at or near the ambient air’s wet-bulb temperature rather than the higher, sometimes much higher, dry-bulb temperature. Many chillers are designed to work in reversed mode to provide heating when required (see Chapter 27).
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Figure 13.7 Air-cooled water chiller, nominal 600kW capacity with two R134a refrigerant circuits, single shell and tube evaporator, and capacity controlled semi-hermetic screw compressors (Airedale) |
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Figure 13.8 Water-cooled water chiller, nominal 250 kW capacity with two R407C refrigerant circuits, brazed plate heat exchangers (1 evaporator, 2 condensers), and multiple scroll compressors (Airedale) |
Chiller ratings, in accordance with EN14511, refer to the entering and leaving chilled fluid temperatures and either the ambient air condition (air-cooled) or the cooling water entering and leaving temperatures (water-cooled).
Posted in Refrigeration and Air Conditioning