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Ground source heat pumps (GSHP) are the ideal energy source for space heating and, in some cases, they can pre-heat domestic hot water.
The heat pump will produce 3-4 kW of heat for each 1 kW of electricity used depending on the coefficient of performance (CoP) of the system.
The CoP is simply the measurement of efficiency of a GSHP system.
The CoP is the ratio of units of heat output for each unit of electricity used to drive the compressor and pump for the ground loop.
As well as ground source heat pumps, air source and water source heat pumps are also available.
A typical 6 - 8kW GSHP system can cost 8,000 -12,000 plus the price of connection to the distribution system. This can vary with property and location.
There are three important elements to a GSHP:
1) The ground loop. This is comprised of lengths of pipe buried in the ground, either in a borehole or a straight horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe to absorb heat from the ground.
2) A heat pump. This has three main parts:
the evaporator - to absorb the heat from the mixture of water and antifreeze in the ground loop;
the compressor to pump the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit;
the condenser that transfers heat to a hot water tank which feeds the distribution system.
3) Heat distribution system. Consisting of under floor heating or radiators for space heating and in some cases water storage for hot water supply.
What to keep in mind when considering a ground source heat pump.
The type of heat distribution system. GSHP Systems can be combined with radiators but under-floor heating is better as it works at a lower temperature (30-35C) .
Is there space available for a trench or borehole to accommodate a ground loop? Is the ground suitable for digging a trench or borehole?
What fuel is being replaced? If it's electricity, oil, LPG or any other conventional fossil fuel the payback will be more favourable. Heat pumps are a good option where gas is unavailable.
Want to be 100% renewable? Buy green electricity, or install solar PV or some other form of renewable electricity generating system to power the compressor and pump.
Is there also a cooling requirement? GSHP Systems can work in reverse to cool a building in the summer.
Is the system for a new building development? Combining the installation with other building works can reduce costs. Wall, floor and loft insulation will lower your heat demand and reduce costs.
Further information:
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