Radiation from the sun heats the earth’s ground. The earth then stores the heat and maintains a temperature of around 10°C, either just below the surface or up to 2m down. It maintains this temperature even through the winter when temperatures can drop below zero on the surface.
The pipes for a ground source heat pump system are commonly buried horizontally in a trench about a metre below the ground, providing there is enough space to do this. Alternatively, boreholes can be drilled down to extract heat from further below the surface.
The way a GSHP works is by circulating a non-toxic Glycol fluid through a buried ground loop. The heat from the ground is absorbed at low temperature by the liquid which then passes through a heat exchanger in the heat pump.