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Heat pump and COP

A heat pump or refrigerator uses work to move heat from cold to hot, the opposite of nature's own direction. Performance is measured with COP instead of efficiency, and COP can be greater than 1 because the machine moves heat rather than creating it.

COPheat=QHWCOP_{heat} = \dfrac{Q_H}{W}COP for heating
COPheat=COPcold+1COP_{heat} = COP_{cold} + 1relation between the two COPs

Symbols

COPheatCOP_{heat}performance factor for heating
COPcoldCOP_{cold}performance factor for cooling

Example

A heat pump with COPheat=3.2COP_{heat} = 3.2 must deliver 88 kW of heat. The electric power needed is W=QH/COPheat=8/3.2=2.5W = Q_H/COP_{heat} = 8/3.2 = 2.5 kW.

COP>1COP > 1 does not mean energy is created – the machine only moves heat and uses work to do so.
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Part of Thermodynamics: Thermodynamic cycles.