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How does it work?

Shoreham Parish Council How does it work?

The ground is warmed by the sun and, some way below the surface, the temperature remains fairly steady at 10-12°C throughout the year. There are two different ways of making use of this heat energy:

In a closed loop system, a number of boreholes are drilled down to a depth of about 150m and a closed loop of pipes installed in the boreholes. Fluid (a mixture of water and antifreeze) is pumped down the loop of pipes, absorbs the heat energy and comes back up warmer to the surface.

In a chalk area, such as Shoreham, underground aquifers can offer a suitable source of tepid water. In this case an open loop system can work. One or two boreholes are drilled to a deeper level to reach the aquifer and water is pumped up to the surface. There, only the heat is absorbed - the water itself is recycled back into the aquifer.

In either of these systems, the temperature of the water is raised to much more useful levels by heat pumps at the surface. These work like a refrigerator in reverse - using electricity in the process but very efficiently. Every unit of electricity (kWh) used by the pumps produces 3 or 4 times that amount of heat energy.

The heat pumps may be grouped together centrally or in clusters so that hot water can be circulated through the underground network to homes and other buildings. Otherwise, tepid (ambient) water is circulated round the network to a heat pump at each individual building.