HEAT PUMPS

Basic concept

A heat pump is basically a fridge in reverse, extracting large volumes of low temperature energy from one source and compressing it into smaller volumes of a higher temperature, for use into another location (i.e. building). The ultimate source of all of this free energy is the Sun!

Heat energy may be extracted from ambient air, water, soil or bedrock. An electrical power supply is required to drive the compressor in the heat pump. Generally for every unit of electricity used 3-5 units of equivalent heat are produced.

Different types of heat pumps

Basic Technology

Ground Source heat pumps (GSHP) extract heat from the earth, which, at around 1.5 metres down, stays at an average temperature of about 11°C-12°C throughout the year (there is some seasonal variability but at this depth the collectors are not directly affected by ground frost). Heat is transfered via a ground loop into your building to provide space heating, and in some cases, heating of domestic water.

There are three key elements to a GSHP: the ground loop collector, the heat pump unit, and the heat distribution system. The ground loop consists of plastic pipe buried in the ground either in horizontal trenches or bore-holes. The pipes are filled with anti-freeze and are in a closed system. This fluid circulates and absorbs heat from the ground. The fluid passes to the heat pump where the energy is extracted. The heat distribution system is the final stage, which can be in the form of under floor heating systems or radiators. Under-floor heating is generally the best distributor of this energy given the relatively low temperature that it operates at.

Examples of Ground Loop-

Air Source heat pumps extract energy directly from the air. An external air source pump extracts energy from the air outside a building (and can work even when external temperature falls to -20°C) and an internal air source pump extracts energy from the air within the house (in other words it can make use of heat already generated in kitchens, showers and bathrooms, for example). Systems can be arranged to return pre-warmed fresh external air, which is particularly useful in modern, well insulated buildings with a potential for 'sick building' syndrome due to lack of air circulation. Such an arrangement should be differentiated from some 'air-con' systems that circulate the same air within a building.

Heat pumps in a building

This technology may be used for space and water heating and may be combined very effectively with heat recovery and dehumidification. All our systems may be weather compensated (ie the heat pump controls adjust according to the outside weather conditions thus improving running efficiencies).

Costs

For a typical family house, the over-all cost ranges from £12,000 for a system using trenches to £16,000 for a system that uses bore-holes. Grant funding can significantly reduce these costs.

Grants

Grants are available from the Energy Saving Scotland home renewables grant shceme as a rebate offering up to 30% of the installation costs subject to a maximum of £4,000 (households). More information can be found at the Energy Saving Scotland home renewables grant scheme


Funding


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