Draft PPS18: Renewable Energy
Annex 1 Ground Source Heat Pumps: Technology
H4. To access thermal energy, coils or loops of special grade pipe need to be buried in the ground either in horizontal trenches or vertical boreholes. Horizontal trenches are a cheaper option and generally used where there is sufficient space. Where there is not enough land to do horizontal trenches, vertical boreholes can be used, these normally require to go down at least 60 meters and are the more expensive option, but will provide higher efficiencies since the temperature of the earth is higher at greater depths, and less power is needed to pump the fluid around the circuit. The length and size of ground loops is designed to match the heating needs of the property. The trenches or boreholes required for the ground loops can be dug and backfilled by a standard earth excavator.
H5. Systems operate by circulating water (or another fluid) through pipes buried in the ground. The water in the pipes is lower than the surrounding ground and so it warms up slightly. This low grade heat is transferred to a heat pump, which raises the temperature to around 50°C. The heat pumps typically providing 4 units of energy from 1 unit of electricity.
H6. The building plot will need sufficient land available for installation of the ground works. The dimensions of trenches or boreholes will vary between manufacturers. The ground above where heat pipes are installed can be used for open space or covered over with hard materials. Where there are existing lakes or ponds or where it is proposed to install Sustainable Urban Drainage Systems (SUDS), the opportunity to install ground source heat pumps beneath the surface of the water should be considered. Similarly in larger developments with open space requirements, ground source heat pumps could be laid beneath green spaces.