Ground source heat pumps (GSHPs) extract heat from the ground using pipes (ground collectors) in either a closed loop system or open loop system. Unlike an Air Source Heat Pump (ASHP), the GSHP is an indoor unit, therefore provision must be made for heat pump and cylinder.
The heat is carried in a liquid mixture of water and anti-freeze and circulated through the ground collectors, (pipework in the ground) through a heat exchanger at the heat pump. The heat pump then transfers this energy to the cylinder, creating separate hot water for both domestic hot water and central heating.
Since the ground below the surface stays at a constant temperature, the heat pump can be used efficiently all year round. Boreholes are often a more efficient energy source because the deeper you go the less effect air or surface ground temperature has. Horizontal loops are closer to the surface and therefore low temperatures can have an effect on yearly efficiency. All of this can be calculated from a site survey.
Depending on the size, age and fabric of your home your heat losses will determine the size of your heat pump and how long the ground collectors need to be. The longer the loop, the more heat is drawn from the ground. If there is limited space for horizontal loops, vertical boreholes can be drilled instead.