First, tell us your location so we can offer the best solution for you.

Even in cold conditions the ground temperature 1.5m deep will be constant at around 12-13°C and is available to be absorbed. Ground-source heat pumps do this by circulating gas, at a temperature colder than the ground-loop liquid, cooling the liquid, thereby making it colder than the ground outside the house. Heat travels from a hot thing to a cold thing, just like your teaspoon heats up when you stir your tea or coffee, and so as this liquid then circulates around the ground-loop, heat is collected by the liquid that is colder than the soil in contact with the pipe. The liquid coming back into the heat pump is carrying the heat it has collected back into the heat pump. This liquid then enters the ground-loop exchanger which has the colder gas circulating through it and so it absorbs this heat.