Ground Source Heat Pumps (GSHP), use the principles of heat pump technology to elevate the temperature of water circulated through pipes buried in the ground, up to a usable temperature for space heating. Typically, a ground source heat pump system can generate low temperature hot water up to 55˚C. However, to achieve a high coefficient of performance (COP) an output temperature of only 35˚C is the norm. This lower temperature is ideal when used in conjunction with underfloor heating systems.
GSHP’s are sometimes referred to as a renewable form of energy since they remove heat from the ground which is provided from the heat of the sun and captured within the earth. Power is required though to make heat pumps operate, however, this is usually offset with the amount of energy produced by the earth collectors.
The installation of pipework below ground is either in shallow long horizontal trenches, better known as ‘Slinkies’ or via a number of vertical bore holes. This ground work is expensive and time consuming, and can hold risks in relation to the ground geology when boring down to depths of 70 metres or more. The cost of vertical bore holes can be very costly also, depending on the earth build-up where Horizontal trenching areas should be chosen wisely so as not to sterilise land and prevent it from being used for future developments.
GSHP’s are limited however, when it comes to centrally generating domestic hot water supplies (HWS), since the normal distribution temperature for domestic hot water heating is 60˚C to ensure the elimination of any Legionella bacteria growth. To generate HWS at 60˚C, typically requires a heating water flow temperature of at least 70˚C to overcome heat lost through pipework and equipment. Incoming cold water can be pre-heated by the GSHP system; however, supplementary electric or gas-fired heating would be required.
As with a Combined Heat & Power (CHP) system solution, GSHP systems do not always combine well with solar water heating, because both systems are suited to pre-heating domestic hot water, rather than delivering it at the required storage and distribution temperature of 60-70˚C. However, if the GSHP is sized and designed only to serve the space heating systems, solar water heating can usefully contribute towards the domestic hot water heating, particularly when there is a reasonable domestic hot water demand.
A GSHP system would provide a CO2 emission per annum saving, compared to that of condensing gas fired boilers with stringent building materials and their U-values being ‘relaxed’ to Building Regulation minimums.