Heat pumps

A heat pump takes low grade heat from a source, from the air, water, soil or rock and uses a small amount of electrical energy to move it to where it is needed and deliver it at a higher temperature. It operates on the same principle as a refrigerator, but in reverse.

A compressor pumps fluid that has a low boiling point  through a sealed system. When the fluid is compressed it turns to vapour and absorbs heat from its surroundings (the heat source). The sealed system pumps the compressed gas to a heat emitter (the heat destination), where the gas enters the condenser heat exchanger and is cooled and condensed into a high pressure liquid. The heat released during the process of condensing the refrigerant to a liquid is passed by a the heat exchanger directly into air or transferred to water to heat the building.
The efficiency heat pumps is referred to as the Coefficient of Performance or COP. Depending on the type and the temperature of the heat source, a heat pump could have a COP of 3, 4 or even 5 to 1. So for a heat pump with, say, a COP of 4 to 1, every 1 kW of electricity input would deliver 4kW of heat output. click here for more information