COP (Coefficient of Performance)
The ratio of useful heat (or cooling) delivered by a heat pump to the electrical energy it consumes, measured at a specific operating point.
The coefficient of performance is the instantaneous efficiency of a heat pump or chiller under defined test conditions. A COP of 3.5 means 3.5 kWh of heat for each kWh of electricity; the other 2.5 kWh come from the environment. Because COP exceeds 1, it is not an efficiency in the thermodynamic sense, and it is never quoted as a percentage.
COP_cooling = Q_C / W (often expressed as EER)
COP_heating = COP_cooling + 1 (ideal cycle, same conditions)
Carnot: COP_H,max = T_H / (T_H - T_C) in kelvin
COP depends strongly on source and sink temperatures. EN 14511 test points are written like A7/W35 (outdoor air 7 °C, water flow 35 °C). Indicative values for a modern air-to-water unit:
- A7/W35: 4.5–5.2
- A2/W35: 3.5–4.0
- A-7/W35: 2.6–3.0
- A7/W55: 2.8–3.3
A rule of thumb is that each 1 K reduction in flow temperature improves COP by roughly 2–3%. Because a single test point says little about annual performance, buyers should compare SCOP or seasonal performance factor (SPF) instead. Estimate running costs in the ground-source heat pump calculator.
Related terms
All terms →- SCOP (Seasonal COP)
A heat pump's average coefficient of performance over a standardised heating season, weighting test points by how often each outdoor temperature occurs.
- Heat pump
A device that uses a refrigeration cycle to move heat from a cooler source (air, ground, water) to a warmer sink, delivering 2–5 units of heat per unit of electricity.
- Air-source heat pump
A heat pump that extracts heat from outdoor air, supplying space heating and hot water (air-to-water) or warm air (air-to-air), and the most widely installed type.
- Ground-source heat pump
A heat pump that exchanges heat with the ground through buried loops or boreholes, benefiting from stable soil temperatures for high seasonal efficiency.
- SEER
Seasonal Energy Efficiency Ratio: total cooling output over a cooling season divided by electricity used, in BTU/Wh (US) or W/W (EU).