Renewables | Air Source

Air SourceAn air source heat pump (ASHP) is a heating and cooling system that uses outside air as its heat source and heat sink. 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.

In domestic heating use, an ASHP absorbs heat from outside air and releases it inside during winter, and can often do the converse in summer. When correctly specified, an ASHP can offer a full central heating solution and domestic hot water up to 80°C.

Outside air, at any temperature above absolute zero, contains some heat. An air-source heat pump moves ('pumps') some of this heat to provide hot water or space heating. This can be done in either direction, to cool or heat the interior of a building.

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 a water tank or indoor heating system, such as radiators or under-floor circuits

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 high price of electricity versus gas (where available). Gas may cause higher carbon emissions, depending upon how the electricity is generated.

A "standard" air sourced heat pump found in most homes can extract useful heat down to about -5F or 0F (-18C). At colder outdoor temperatures the heat pump is inefficient; it could be switched off to run only on supplemental heat (or emergency heat) if the supplemental heat is sized large enough. There are specially designed heat pumps that, while giving up some performance in a/c mode, will provide useful heat extraction to even lower outdoor temperatures. An air source heat pump designed specifically for very cold climates can extract useful heat from ambient air as cold as -20F or even -25F (-30C), but these are uncommon in most homes.