Ground Source Heat Pumps
Ground Source heat pumps use the higher temperature that is always present below ground to heat refrigerant in a long run of piping acting as a heat exchanger. In effect this is using a similar process to refrigeration except it is reversing the cycle.
Up at the surface the temperature is raised through expansion of the refrigerant into the gas phase so that heat energy can be extracted for space or liquid heating. It is the same cycle that is used as in refrigeration except that instead of creating waste heat and useful cooling the heat pump is creating useful heat and waste cooling.
Since the ground is always warmer the lower down you go the removal of some of that heat can be a highly efficient means of utilising electrical energy. Rather than using electricity for direct heating, powering a compressor to drive the “refrigeration” cycle can result in far greater efficiencies, especially if that electricity can be obtained from renewable sources such as wind, solar or hydro.