Ground source heat pumps collect energy via a borehole collector (vertical collector)
Heat energy is collected in a similar way to the surface ground collector and transferred to the ground source heat pump except the u-shaped collector piping is sunk into a borehole. The total borehole depth is again dependent on the output of the ground source heat pump and can be achieved across a number of separate boreholes which should normally be at least 15 metres apart. Where the ground source heat pump is both heating and cooling the boreholes can be closer together. Typically, the depth required for a house can be between 70 and 190 metres.
Borehole collectors are specially manufactured plastic pipes with a u-bend and weight and are sunk into each borehole. Where more than one borehole is required, the borehole collectors are connected to a manifold via a network of surface collectors. The manifold can be integrated in a chamber dug into the ground close to the building and then one flow and return pipe is then run from the manifold chamber into the plant room and connected to the ground source heat pump.
Because a borehole needs to be drilled by an experienced contractor using specialist plant, this method tends to be more costly but clearly requires far less space than the horizontal method. Permits may be required depending on local conditions e.g. mine workings, tunnels etc.
Alan Brocket, general manager of drilling contractor, Rocklift, explains the stages involved in drilling a borehole for collecting heat energy for a ground source heat pump.