Heat Pumps
Electrical heat pumps are very efficient because they use conventional refrigeration technology to extract the energy stored in the environment. Air source heat pumps use the outside air as their energy source while ground source heat pumps extract heat from the earth using pipes that are buried beneath the ground.
The energy is transferred to the heat pump’s refrigerant which rises in temperature and changes from a liquid to a gas. The heat pump’s compressor then compresses the refrigerant gas which reduces in volume and increases in temperature. The heat pump’s heat exchanger (condenser) then uses the heat from the hot refrigerant to heat water for central heating or hot water. The cooled refrigerant turns back into a liquid and the cycle starts again.
In simple terms, the heat pump’s coefficient of performance (COP) is the ratio of the total usable energy extracted in the form of heat from the environment and the amount of electricity used by the heat pump. Therefore, a heat pump that produces 4 kilowatts of heat energy, while using only 1 kilowatt of electricity to produce it, will have a COP of 4.
A more precise definition is available from the Heat Pump Association’s website which has a useful glossary of terms.
In a ground source heat pump, the COP will vary with the ground temperature and the required temperature of the heating system. This is explained on the Kensa Engineering website.