COP — Coefficient of Performance

Definition

The COP describes the efficiency of a heat pump at a fixed, steady-state operating point. It expresses the ratio of delivered heating output in kilowatts to the electrical power input in kilowatts. A COP of 4.0 means that 1 kW of electricity produces 4 kW of heat. Unlike the Annual Coefficient of Performance (JAZ — Jahresarbeitszahl), which reflects seasonal average efficiency over a full heating year, the COP is a laboratory value. Measurements follow the European standard EN 14511 under precisely defined source and flow temperatures. Common test points are A2/W35 (outdoor air 2 °C, heating flow temperature 35 °C) or B0/W35 (brine inlet 0 °C, flow 35 °C). Because the COP depends strongly on the temperature difference between source and sink, it drops noticeably with colder outdoor air and higher flow temperatures. A sound heat pump design therefore considers several operating points and complements the COP with a JAZ calculation according to VDI 4650.

When is the term used?

In practical heat pump design the COP serves mainly to compare devices and manufacturers. Because manufacturers often state COP values under favourable conditions, a meaningful comparison is only possible when the same operating points are used. The source and sink combination is particularly important: a COP of 5.1 at A7/W35 says little about real winter design performance. For the later economic assessment, the JAZ is more decisive because it also accounts for defrost phases, auxiliary energy and actual operating hours. BAFA heating funding eligibility is likewise evaluated via the JAZ, not the COP. Even so, the COP remains a valuable benchmarking tool during initial device selection.

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