Air at any temperature above absolute zero contains some energy. An air-source heat pump transfers (‘pumps’) some of this energy as heat from one place to another, for example between the outside and inside of a building. This can provide space heating and/or hot water. A single system can be designed to transfer heat in either direction, to heat or cool the interior of the building in winter and summer respectively. For simplicity, the description below focuses on use for interior heating.
The technology is similar to a refrigerator or freezer or air conditioning unit: the different effect is due to the physical location of the different system components. Just as the pipes on the back of a refrigerator become warm as the interior cools, so an ASHP warms the inside of a building whilst cooling the outside air.
The main components of an air-source heat pump are:
- An outdoor heat exchanger coil, which extracts heat from ambient air
- An indoor heat exchanger coil, which transfers the heat into hot air ducts, an indoor heating system such as water-filled radiators or underfloor circuits and/or a domestic hot water tank
Air source heat pumps can provide fairly low cost space heating. A high efficiency heat pump can provide up to four times as much heat as an electric heater using the same energy.
A “standard” domestic air source heat pump can extract useful heat down to about −15 °C (5 °F).