Geothermal (or geoexchange) energy is produced by harnessing the Earth's natural geological heat source and converting it into a source that can heat a domestic property.
The Earth is normally around 55°F (12.8°C) and this heat can be utilised by the use of ground source heat pumps.
Certain geological characteristics aid the production of geothermal power such as geysers or hot underground magma deposits.
Iceland takes advantage of the country's unique geological make up to use geothermal power to great effect. Currently 17% of Iceland's total electricity production is derived from geothermal energy.
There are three main components required to introduce a geothermal Ground Source Heat Pump (GSHP) installation into a domestic environment and they are detailed below.
- Ground loops.
A ground loop is a length of pipe buried in the ground which contains a mixture of water and anti-freeze - this is pumped around the pipe to absorb the natural heat from the ground.
There are three main types of ground loops available and you should make a determination on their characteristics and site conditions to decide which would provide the best solution for your situation.
The three types of ground loop in a Ground Source Heat Pump (GSHP) system are; the borehole, straight horizontal and spiral horizontal. For obvious reasons you would require more land for a horizontal trench than a borehole and boreholes actually cost more to develop than horizontal trenches. For example, a spiral horizontal trench of 10m in length would provide approximately 1kW of heating for your home.
- Heat Pump system.
The heat pump system would consist of an evaporator, a compressor and a condenser and is similar to those used in refrigeration units.
- Distribution system.
This is the system that delivers the heat to under floor heating or radiators in the home. It is also possible to store hot water generated using a GSHP system.
Cost and Viability
It is important to consider whether you have the land available for underground piping and whether that land is suitable to dig trenches. If there is available space, one can usually purchase a standard 8kW system for between £6,500 and £9,500 (distribution system not included). The efficiency of this type of system is measured by the Coefficient of Performance (CoP) and this is used to measure the ratio of heat produced to the amount of electricity used to drive the compressor and the pump. For this system the typical CoP is between 2.5 and 4 - in other words, for each unit of energy used to drive the system you can expect to recover 2.5 to 4 units. Based on this CoP, a geothermal system would be cheap to run than an oil system or electric storage heaters.
If you wish to make the system even more environmentally friendly then you could even go as far as installing photovoltaic solar panels to produce the electricity to drive the system! Of course, if this is not a viable option you could obtain your electricity from a green energy supplier instead.
It is possible to reduce your heating demand substantially by making your home more energy efficient and by installing additional insulation such as loft insulation, cavity wall insulation and draught-proofing. If your home is not already fitted with double-glazing then having it installed would produce a dramatic increase in the energy efficiency of your home and a very significant reduction in your energy requirements and associated costs.
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