A ground source heat pump, also known as a shallow geothermal heat pump, works by absorbing heat from the ground and transferring the heat into buildings as hot water.
The heat pump works on the same principles as a domestic fridge. In your fridge a heat pump extracts heat from the inside and transfers it to a small radiator at the back, where the heat is dissipated into the room.
In exactly the same way a ground source heat pump takes heat from the ground and transfers the heat into the building by circulating hot water though radiators, or underfloor heating pipes.
A heat pump works by increasing the temperature of a fluid it contains at the temperature of the ground using a cycle of compression and evaporation of a thermal transfer fluid fluid. When a large volume of gas is compressed into a small space the heat energy in the gas becomes concentrated, causing the gas to heat up. When the gas is then depressurised, and turns back into a liquid, energy is released. A heat pump uses a heat exchanger to capture the released energy and transfers the heat as hot water into the heating circuit of the building and hot water supply system.
Once the highly pressurised gas has condensed, and released its heat, it then becomes very cold. The heat pump uses a heat exchanger to transfer that cold fluid back into the ground where it absorbs heat from the surrounding ground and the cycle can begin again.