coefficient of performance

The coefficient of performance or COP (sometimes CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work (energy) required. Higher COPs equate to higher efficiency, lower energy (power) consumption and thus lower operating costs. The COP is used in thermodynamics.
The COP usually exceeds 1, especially in heat pumps, because instead of converting work to heat (which has a maximum efficiency of 100% or COP of 1), they use work to move existing heat from one place to another. Less work is required to move heat than for conversion into heat, and because of this, heat pumps, air conditioners and refrigeration systems can have a coefficient of performance greater than one. Most air conditioners have a COP of 3.5 to 5.
While the Coefficient of Performance is a term commonly used with heat pumps, it is also applicable to any energy system that behaves in a thermodynamically open manner, receiving energy from the local environment, whether it be electromagnetic, electrostatic, or any other viable form. The key difference between the dimensionless term efficiency and CoP is that the denominator in the latter is the energy input provided by the user or operator only, to differentiate it from that supplied by the local environment.
As an example, if a heat pump has an internal compressor efficiency of 70% and the user supplies 1.2kW of power to run the unit and 6.5kW is drawn from the local thermal environment, then the efficiency-moderated output is 75% of a total of 7.7kW = 5.8kW. The CoP will therefore be 5.8/1.2 = 4.8
The COP is highly dependent on operating conditions, especially absolute temperature and relative temperature between sink and system, and is often graphed or averaged against expected conditions.
Performance of absorption refrigerator chillers is typically much lower, as they are not heat pumps relying on compression, but instead rely on chemical reactions driven by heat.

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