Air Source Heat Pumps
An air source heat pump extracts heat from the outside air in the same way that a fridge extracts heat from its inside. It can extract heat from the air even when the outside temperature is as low as minus 20°C.
Air source heat pumps can be one of the most cost effective methods of realising a renewable energy source as free energy. Ambient temperature is always available in the atmosphere and there is no necessity for disruptive and sometimes expensive ground collector installations as with ground source systems.
The term coefficient of performance (COP) is used to describe the ratio of useful heat movement to work input. When used for heating on a mild day of say 10°C, a typical air-source heat pump has a COP of 3 to 4, thats a 300% to 400% increase in efficiency!