A heat pump comprises two heat exchangers called the evaporator and the condenser, a compressor, an expansion valve and the refrigerant which is pumped around the system. To complete the system, a collector is required to extract the low grade heat from the source and a distribution system to distribute and store the high grade heat.

Components of a ground source heat pump system

There are heat pump systems which are suitable both for retrofitting and new homes. As source it is possible to use the air, ground or water, the latter two sources having higher efficiency because the source temperature hardly varies during the winter.