Ground Source Heat Pumps

Although Ground Source Heat Pumps (GSHP’s) have been widely used for many years in North America and many parts of Europe, including Sweden, they are a relatively new phenomenon in the UK. They make use of heat occurring naturally in the ground which is renewed by the sun’s energy on warm days. These heat pumps provide one of the most clean and energy-efficient ways of heating buildings.

Contrary to some beliefs, they do not work on geothermal energy (which needs hot rocks or springs) and can therefore be installed throughout most of the UK.

GSHP’s are powered electrically but will typically deliver three to four times as much energy as they consume. They cost more to install than traditional heating systems and much of this is due to the ground works that are necessary. However, their low running and maintenance costs, coupled with a life expectancy of over 20 years, make them an impressive long term investment.

GSHP - Surface Collector

The surface collector requires shallow trenches to be dug adjacent to the building so that the collecting pipes can be laid approximately 1m below the surface. The pipes can be laid straight as shown or more compactly in a coiled “slinky” style. As shown by the colours of the pipes in the figure above, the pumped fluid exiting the building is cold but gradually warms as it passes though the pipes in the soil. By the time it has returned to the building it has absorbed useful heat energy that can be extracted by the Heat Pump for use in the house. The fluid is water with an anti-freeze mix.

GSHP - Bore Hole

In the borehole arrangement, the collecting pipe loop is installed into boreholes. The depth and number of holes is dependent upon many factors but the rock and earth structure, its ability to convey its heat energy at each layer, and the depth of the water table are all contributing factors. Depths of over 100m are certainly not uncommon. Once the pipes are installed into the boreholes, the holes are then backfilled with a grout which protects the loop, stabilises the hole and enhances the conductivity between the earth and collecting pipe. As in the Surface Collector arrangement, the fluid is very cold when it exits from the building. However, it collects heat on its journey to the bottom of the borehole and back and returns to the building in a relatively warm state ready for the Heat Pump to use.

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