Air-source heat pumps

An air source heat pump (ASHP) is a system which transfers heat from outside to inside a building, or vice versa. Under the principles of vapor compression refrigeration, an ASHP uses a refrigerant system involving a compressor and a condenser to absorb heat at one place and release it at another. They can be used as a space heater or cooler, and are sometimes called "reverse-cycle air conditioners".

In domestic heating use, an ASHP absorbs heat from outside air and releases it inside the building, as hot air, hot water-filled radiators, underfloor heating and/or domestic hot water supply. The same system can often do the reverse in summer, cooling the inside of the house. When correctly specified, an ASHP can offer a full central heating solution and domestic hot water up to 80 °C.

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:

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. In comparison to gas as a primary heat source, however, the lifetime cost of an air source heat pump may be affected by the price of electricity compared to gas (where available). Use of gas may be associated with higher carbon emissions, depending upon how the electricity is generated.

A "standard" domestic air source heat pump can extract useful heat down to about −15 °C (5 °F). At colder outdoor temperatures the heat pump is less efficient; it could be switched off and the premises heated using only supplemental heat (or emergency heat) if the supplemental heating system is large enough. There are specially designed heat pumps that, while giving up some performance in cooling mode, will provide useful heat extraction to even lower outdoor temperatures.

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Wikipedia