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Geothermal
Ground Source Heat Pumps
Heat pumps use the same heat transfer principles as refrigerators, but in reverse. This means that they can draw useful heat into the house from the ground which is a source of low level heat. The ground is heated by the sun all year round, and at a depth of around 1 metre is at a temperature of 11-14ºC. A GSHP can convert this heat to 40-50ºC for heating purposes.
What's needed?
- Sufficient ground around your property to put in the ground loop at 1metre depth
- If space is restricted a vertical bore hole can be used
- Good insulation and preferably underfloor heating
A GSHP can take heat stored by the earth and use it to heat a house or pre-heat hot water. When sized correctly, GSHPs can provide all of a property’s heating requirement, even on the coldest of winter days, thus replacing your conventional boiler.
When heating a house, GSHPs are best used in conjunction with hot-water underfloor heating under a stone or tiled floor.It is not recommend for use with a conventional radiator system.
The heat pump is approximately the size of a domestic fridge, and is best located in a utility room, garage or outside. This is what converts the low-grade heat drawn from the ground to a higher more useable heat. Inside the heat pump unit, compressors and pumps circulate the water-antifreeze mix around a ground loop.
The 'ground loop' is a system of pipes buried in the ground which the GSHP uses to absorb heat from the ground. The ground loop needs to be buried, either in a vertical borehole (when space is limited), or more usually in a long horizontal trench. The trench option is cheaper, but requires more area. Typically, in domestic situations, there would be a trench 0.3m wide, 1.0m deep and 50-150m long. This can be laid in any formation or direction but the pipes must be 1m apart.
The inside view
Is it economically and environmentally viable?
A GSHP plus underfloor heating is generally more economic than heating the house using oil or electricity, but slightly more expensive than gas.
The main environmental impact is from the electricity used to run the heat pump, although this can be offset with a solar electric system or green energy tariff. Generally, for every unit of electricity needed to run the pump, 4 units of heat energy is gained in the property.
In terms of the total carbon emissions, even using mains electricity, it is more efficient than the most efficient gas or oil condensing boiler
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