What is a Ground Source Heat Pump (GSHP)?
Ground Source Heat Pumps absorb heat from the ground to heat buildings. As with Air Source Heat Pumps, GSHP’s require electricity to power the pump and are therefore not 100% “renewable” if the electricity is sourced from a standard utility tariff. However, for every unit of electricity used to power the pump, 3 to 4 units of heat are generated, making GSHP’s highly efficient. GSHP’s can be set up to deliver heat via water for under floor heating & radiators but also to pre-heat hot water for domestic use (i.e. baths / showers etc).
Why Install a GSHP?
Once a GSHP is installed it provides an unobtrusive renewable energy solution for homes with limited roof space (for solar) or low wind speeds. Additionally, GSHP’s operate more efficiently than ASHP’s at lower temperatures & the ‘coefficient of performance’ (CoP) is greater than for Air Source Heat Pumps.
How does a GSHP work?
There are 3 parts to a GSHP, the ground loop, the heat pump and the heat distribution system. The ground loop can be installed in 3 configurations, horizontally as a pipe, horizontally as a ‘coil’ or vertically in a borehole. In the case of horizontal installations the ground loop is placed approximately 1m beneath the surface, with the ‘pipe’ option requiring a greater area than a ‘coil’.
The heat pump is similar to a domestic refrigerator ‘in reverse’, in that it employs an evaporator, a compressor and a condenser to produce hot water instead of absorbing heat.
Finally, the heat distribution system will usually be an under floor heating system or radiators. It should be noted that larger radiators are often recommended if the GSHP is to be the only source of heat generation as the operating water temperature supplied by the GSHP is 45%, significantly lower than in conventional central heating systems. However, in most cases, the existing boiler is retained with the water generated by the GSHP being used to preheat the water to 45% and the boiler generating the final 20° – 30°.
Will it work for me?
The three options for the ground loop configuration mean that GSHP’s can be installed in most domestic locations where there is a minimum of 50m2 of external space, although at this lowest surface area a bore hole would be the only option and requires specialist installation which will increase costs. As a rough rule of thumb for an installation with a horizontal pipe configuration, two & a half times the surface area of the house to be heated is required outside. This can be significantly reduced by the installation of coils. As with most Cleantech solutions, GSHP’s work at a lower temperature than a conventional boiler system & its important that the property has been properly insulated and draught-proofed.
Without these modifications and especially in older properties, the benefits of heat pumps can be questionable. Further, replacing or supplementing an existing oil-fed, electric or LPG heating system with a heat pump will be far more advantageous than in a house on the gas grid.
Finally, heat pumps do require changes in owner behaviour compared to conventional systems. As they run at lower temperatures and take longer to bring a room up to temperature, it is more efficient to have the heating on much longer than with a conventional system. This requires more planning than with a conventional system as is something that most of us are unused to. Failure to change you heating habits will however negate many of the financial and environmental benefits.