In principle, geothermal heating works like a refrigerator – only in reverse operation: It extracts heat from the subsurface and transfers it to the house.
A heat exchanger is usually used initially to generate geothermal energy. Water or a heat transfer fluid circulates in a closed pipe system underground and absorbs the ground’s heat. In a good system, the groundwater circulates in two open wells. This heat is transferred to the heat pump at the surface. A working medium circulates in the pump that evaporates at very low temperatures (the refrigerant) and absorbs the heat from the heat transfer fluid.
The evaporated refrigerant is now strongly compressed in a compressor. The higher pressure also increases the temperature significantly. You can easily try this effect by yourself with a bicycle air pump: it gets warm when you pump and close the outlet. After leaving the compressor or opening the compressor, the hot medium gives off its heat, which is now sufficient for heating operation, to the heating system, where it cools down and liquefies again. It then re-enters the low-pressure area through an expansion valve, whereby it continues to cool. It, therefore, absorbs the heat from the earth, and the cycle starts all over again.
Geothermal heat pump needs the energy to drive the compressor, which is usually supplied in the form of electricity or gas, determining its efficiency. With an annual coefficient of four performances, for example, a heat pump generates four-kilowatt hours of heating from the one-kilowatt hour of electricity. It is already working very effectively and always environmentally friendly. You can achieve a further improvement in the CO2 balance of your geothermal system by using electricity from renewable sources. Because then you will no longer cause any climate-damaging CO2 emissions with your heating.