Ground source heat pumps use loops of pipe beneath the ground, these are either laid in trenches or placed in boreholes. Around 1 metre below the ground there are stable temperatures of around 8-10°C all year round. The pipes below the ground contain a brine mixture of water and antifreeze. As this mixture moves around the loop, it extracts heat from the surrounding ground.
This low temperature heat is transported to the heat pump unit. Here in the heat exchanger, also known as an evaporator, the brine meets the ice-cold refrigerant which is then heated by a few degrees and evaporates.
This is transferred to a compressor which raises the pressure of the refrigerant, which in turn further raises its temperature. This heat is transferred by the heat exchanger (condenser) to the heating system where it is used to heat radiators or underfloor heating and domestic hot water.
Meanwhile, in the heat pump the refrigerant reverts from a gas to a liquid and passes through an expansion valve to lower the pressure and to reduce the temperature. This is then cycled back through the system.