GSHP System Introduction
Ground source heat pumps provide a new and clean way of heating buildings all over the world. They make use of renewable energy stored in the ground, providing one of the most energy-efficient ways of heating buildings. They are suitable for a wide variety of building types and are particularly appropriate for low environmental impact projects.
The only energy used by Ground Source Heat Pump System is electricity to power the pumps. Typically, a Ground Source Heat Pump will deliver 3 or 4 times as much thermal energy (heat) as is used in electrical energy to drive the system. For a particularly environmental solution, green electricity can be purchased.
Ground Source Heat Pump System have been widely used in other parts of the world, including North America and Europe, for many years. Typically they cost more to install than conventional systems; however, they have very low maintenance costs and can be expected to provide reliable and environmentally friendly heating for in excess of 20 years.
Ground Source Heat Pumps work best with heating systems which are optimised to run at a lower water temperature than is commonly used in UK boiler and radiator System. As such, they make an ideal partner for underfloor heating System
How do they work?
Radiation from the sun heats the earth. The earth then stores the heat and maintains, just a metre or so down, a temperature of around 8-12℃ even throughout the winter. Thanks to ground source heat pumps we can now tap into this constantly replenished heat store to heat buildings and even to provide hot water. The technology used is the same as that used in refrigerators. Just as a fridge extracts heat from the food and pumps it into the kitchen so a ground source heat pump extracts heat from the earth and pumps it into a building.
How efficient are Ground Source Heat Pumps?
For every unit of electricity used to power the heat pump system, approximately 3-4 units of heat are captured and distributed. In effect this means a Ground Source Heat Pump is 300-400% efficient in terms of its use of electricity. At this efficiency level there will be less carbon dioxide emissions than for a gas boiler heating system. In many cases it may also be possible to provide the required electricity by means of renewable energy, thus virtually doing away with any use of fossil fuels and reducing carbon emissions to zero.
What do they look like?
A Ground Source Heat Pump System comprises three basic elements - a ground loop, the heat pump itself, and a heat distribution system.
The ground loop is a pipe buried underground in either a horizontal trench or a vertical borehole. Horizontal trenches are dug 1.5 - 2 metres below ground level and, although using more land than a borehole, are usually cheaper for smaller system.
Boreholes are drilled to a depth of between 15 - 150 metres and benefit from higher ground temperatures than trenches. However, there are a variety of types of pipe (eg the coiled pipe known as a ‘slinky') which can be used in a trench instead of a straight one, which increase the amount of heat absorbed from the ground and so enhance performance. The size of ground area required for trenches will vary with the location, the property and the output required. As a very general guide, for a newly built 3-bedroomed house of around 120 ㎡ in area with a heat loss of around 6kW, two trenches of 30-40 metres in length would probably be required.
A water/anti-freeze mixture is pumped through the pipe where it absorbs heat from the ground. A heat exchanger then extracts the absorbed heat and transfers it to the heat pump.
The third basic element of a ground source heat pump, the heat distribution system, can be either low temperature radiators or, preferably, underfloor heating. If the heat pump is asked to produce higher temperatures, for example in a conventional radiator circuit, then its efficiency will reduce.
Once a ground source heat pump is installed, there are no external fans and no visible external equipment. The system is quiet in operation, very safe and requires very little maintenance.
Installation and Running Costs
Exact installation costs depend on the site and the amount of heat output required. A survey is necessary to ensure that the ground at the location is suitable and to decide whether a horizontal trench or vertical borehole is most appropriate. Again as a very general guide, the installed cost of a typical system would probably be about ￡1,000 per kW. However, this cost may vary greatly depending on the type of property and ground conditions. Savings in running costs of 25% to 50% are possible depending on the type and price of fuel being displaced.