Ground Thermal is a form of heat that is stored in the ground by heat transfer into the clay from the sun. The heat is usually around 16 degrees centigrade and is held by the ground which is insulated by the top layer of soil.

This Low grade heat remains fairly constant all year round at depths of more than two metres, and this heat can be collected through an operation similar in principle to a fridge.

Ground Source Heat Pumps (GSHP) together with a compressor are used to compress and expand the working fluid to gather and release the heat from the ground into the water tank which is used to heat the living space.

The GSHP uses some electricity for the pump and compressor but the COP is around 4:1 producing a much better efficiency than using the same electricity directly to heat the water. There are some problems with this system if the average ground temperature is lowered through constant extraction leaving the ground closer to freezing and affecting the natural flora and fauna in the area.

However if the extraction is not widespread conduction from the surrounding clay will tend to equalise the temperature. This can be facilitated by using the system in reverse during summer and cooling the building by putting the heat back into the ground maintaining an equilibrium which demands prudent use and therefore usually limits the systems contribution to the total heating requirements necessary for human requirements.

For more information:

http://www.energysavingtrust.org.uk/Generate-your-own-energy/Ground-source-heat-pumps

http://www.gshp.org.uk/ground_source_heat_pumps.html

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