| Cooling systems are defined by:
1. The temperatures they can "hold" either in the space and/or the
process or equipment, and
2. The amount of heat they can remove at full capacity.
This heat removal is normally expressed in tons of cooling (or
refrigeration) capacity. One ton of cooling equals precisely 12,000 Btu heat
removal per hour (abbreviated Btuh) and comes from the way air handlers were
originally rated -- that is, how many pounds of ice would have to be loaded
into them to provide the required space cooling. When melting, ice gives up
144 Btu per pound. Therefore, one ton of cooling provides the same amount of
cooling energy as melting one ton of ice in 24 hours.
For any given piece of installed equipment, this rated capacity is
dependent upon the method used by the system to reject heat. For example, a
cooling system rejecting heat to a dry fan-coil condenser will normally
produce fewer tons of cooling on the design day than that same chiller
mechanical system rejecting heat to a cooling tower. Put another way, any
cooling system uses more power (or thermal input in the case of absorption
chillers) to reject heat to a dry (air cooled) condensing system than to a
wet (water cooled) condensing system.
This energy performance is defined by several measures: Coefficient of
Performance (COP), kW/ton, Energy Efficiency Ratio (EER), and similar terms
for thermally activated systems.
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