Ground source heat pumps
When the sun shines on the ground, its heat energy is absorbed into the ground. Ground source heat pumps extract this energy to use for space heating. Strictly speaking it is a form of solar energy and not geothermal as it is sometimes referred to.
How a ground source heat pump works
The heat energy stored in the ground, usually at a constant temperature of about 12 degrees celsius, is absorbed into a water/antifreeze solution circulating in pipes buried in the ground or in bore holes.
The system works like a fridge in reverse by using a pump and compressor to enhance this heat and transfer it to an under floor heating system in the building.
Heat pumps do need some power to operate. However, for each unit of electricity they use they can generate up to four units of heat depending on the outside temperature. This is called the Co-efficient of Performance (COP) and models are rated on their COP.
For maximum efficiency the electricity used can be supplemented by some other renewable such as photovoltaics or wind. The system itself is normally operated on an off peak tariff.
Since the system temperature of 35 to 40 degrees celsius is not suitable for the provision of domestic hot water (DHW) it is normally used with an immersion heater or a solar thermal collector to achieve 60 degrees celsius for DHW use.
Water source heat pumps
A water source heat pump is similar to a ground source heat pump but the property has to be near a suitable river, stream or lake.
Pipes are submerged under the waterbody where temperatures stay constant at about 7-12 degrees. This heats liquid inside the pipes which passes to a heat pump inside the property.
As with ground source heat pumps, some power is required to operate the pump, but water source heat pumps typically produce three to five times the power they use for heating your home.
You may have to get planning permission to fit a heat pump, especially in conservation areas or on listed buildings. Always check with your divisional planning office about planning issues before you have a system installed. Obtaining planning permission after the system is in place can be difficult and expensive.
Remember to insulate first
You should make sure that your property is properly insulated before installing renewable technologies.
NI Energy Advice
NI Energy Advice offers independent and impartial energy advice to domestic householders in Northern Ireland - plus referrals to energy grants and other sources of help.