Ground source heat pumps

Pros

• Probably the most effective renewable energy source for heating domestic hot water
• Works efficiently all year round, even when outside air temperature falls below zero Celsius

Cons

• Tends to be expensive to install in-ground heat absorbing pipework (either as coils in trenches or in boreholes)

Top Tips

• Probably the most efficient renewable energy source for effective, year-round under floor heating (with minimum requirement for heat top up by a conventional boiler)
• Nu-Sustainable can work with your underfloor heating engineer to specify and install the optimum ground source heat pump

After the initial outlay, a ground source heat pump is virtually cost-free, apart from electricity to drive a circulating pump and the compressor in the refrigerant circuit, where the temperature is stepped up to warm the underfloor heating pipes. Low operating costs.

Ground source heat pumps owe their success to the stability of temperatures just a few feet below the topsoil. Even when there is frost or snow on the ground, there is almost constant warmth below the surface. A typical heat pump starts with coiled piping – often referred to as a ground loop – buried in trenches about six feet deep or sometimes in a deeper borehole. Water circulating in the

piping absorbs heat from the surrounding ground. The longer the piping, the more heat can be collected – but as the ground loops get longer, they also need more powerful circulating pumps.

The ground heated water passes through a heat exchanger where the heat energy is transferred to a refrigerant which is compressed to raise the temperature. In a second heat exchanger, the energy in the refrigerant is transferred into water circulating in an underfloor heating system. By reversing the process in the refrigerant circuit, underfloor heating becomes a cooling system.

Ground source heat pumps are sometimes also used to pre-heat water in a more traditional heating and hot water system with a gas boiler as the main source of heat. Pre-heating with ‘free’ energy means a lesser requirement for gas with both cash and emissions saving. Boiler life is also extended.

Efficiency of ground source heat pumps is measured by the Coefficient of Performance (COP) which expresses the heating output in relation to each kW of electricity needed to drive the system: a COP of 3.5 for example indicates that for every 1kW of electricity, the system produces 3.5kW of heating.