Ground source heat pumps absorb heat from the ground into a fluid in the pump.

Requires: External space for installation.

The fluid is then compressed by the pump, heating it up further. The heat is transferred to the heating and hot water circuits of a building.  An advantage of ground source heat pumps compared to air source heat pumps is that the temperature of the ground is relatively constant throughout the year, between 10 and 13°C. As a result, ground source heat pumps’ efficiencies fluctuate less over a year than those of air source heat pumps (1). They are also generally more efficient.

Ground source heat pumps can be horizontal or borehole, depending on the outdoor space available. Horizontal ground source heat pumps require a large land area to be dug up, for example under a car park, for pipework laid at about 2m deep for circulating the fluid, so it can absorb sufficient heat (2). The large area is required due to the shallow depth.

Using a 100kW heat pump as an illustrative example: Assuming 15W of heat extracted per metre of pipe, this equates to 6,667m of pipe. Assuming a 1m wide trench with pipes up and down each side of the trench this is 3,333m of trench. Assuming 100m long trenches, this is 34 trenches. Assuming 4m spacing between trenches, this means the land area for a 100kW heat pump is 100m long by 166m wide (as 34 × 1m + 33 × 4m = 166m) (3).

Borehole or vertical array ground source heat pumps require a much smaller land area but compensate by extracting heat from much deeper underground, typically up to 200m. This depth makes borehole systems more expensive to install due to the drilling required (1).

Once either a horizontal or borehole ground source heat pump has been installed it will not change the usability of the land it is buried under. Ground source heat pumps do not require planning permission.

(1) Energy Saving Trust, Generating Renewable Energy, Ground Source Heat Pumps. Available from: https://energysavingtrust.org.uk/advice/ground-source-heat-pumps/ [Accessed 26^th January 2021].

(2) The Renewable Energy Hub UK, A Complete Guide to Heat Pumps in 2020, Everything You Need to Know About Ground Source Heat Pumps. Available from: https://www.renewableenergyhub.co.uk/main/heat-pumps-information/ground-source-heat-pumps/ [Accessed 26^th January 2021].

(3) Jonathan Price, Isoenergy, How Much Land Do You Need for a Ground Source Heat Pump? Available from: https://www.isoenergy.co.uk/latest-news/renewable-energy-news-from-isoenergy/how-much-land-do-you-need-for-a-ground-source-heat-pump [Accessed 15th March 2021].