Ground and Air Source Heating
A few metres down the earth remains at a constant temperature about 10 – 15 degrees in the UK. We can make use of this fact to transfer this latent heat to your home using a ground source heat pump. Heat pumps draw heat from the ground via a ground collector (slinky) or a ground probe (bore hole).
Heat pumps work in much the same way as a fridge but in reverse. In a fridge the heat is transported from inside to outside, while a heat pump takes heat stored below the underground frost line and transports it via the heating system to the house interior. Some systems are designed to work in reverse as well, cooling the interior in hot weather.
Air source heat pumps use the same principle but extract the heat from the air, rather than the ground. As such their installation is much simpler and cheaper but the available heat is not constant.
These systems require power to drive them, but in an efficient system one kilowatt of energy can generate three kilowatts of heat.
Although the installation of a ground source heat pump to an existing building can be disruptive it has the following advantages:
- Low Operating Cost: provide domestic water heating essentially free or at substantial savings.
- Low Maintenance Costs: fewer mechanical components, making them more reliable, easier to service and less prone to failure. The ground heat exchanger and its associated piping has an expected life of over 50 years.
- Durability: last much longer than conventional HVAC systems because they are protected from harsh outdoor weather.
- Low Noise: systems are among the quietest ever designed.
- Reduced Emissions: do not require external venting, as fossil fuel systems do, so they do not pollute the air.
Under Floor Heating
A heat pump operates most efficiently when the temperature difference between the heat source and the heat demand is smallest. For that reason they are most suited to powering under floor heating systems which typically run at a temperature of 36-40 degrees rather than radiator based heating systems which typically run at 70 degrees plus.
Most ground source system companies also supply and install under floor heating and can advise on your total system requirements.
Geothermal Power Generation
Geothermally generated electricity was first produced at Larderello, Italy, in 1904. Since then, the use of geothermal energy for electricity has grown to about 8,000 megawatts worldwide of which the United States produces 2,700 megawatts. Other countries such as Iceland, New Zealand, the Philippines and Japan that have an active geothermal geology generate in excess of 17% of their electricity requirements this way.
These power plants
- Take steam out of fractures in the ground and use it to directly drive a turbine;
- Take hot water, usually at temperatures over 200°C, out of the ground, and allow it to boil as it rises to the surface then separate and run the steam through a turbine or
- The hot water flows through heat exchangers, boiling an organic fluid that spins the turbine.
The condensed steam and remaining geothermal fluid from all three types of plants are injected back into the hot rock to pick up more heat.
There is only one geothermal power plant in operation in the UK, in Southampton and there is limited potential for further developments as sites need hot rock relatively near to the surface and rock which is sufficiently fractured to allow the passage of (heated) water. There are small areas of suitable hot rocks in the North Pennines, parts of southern England and Derbyshire.
Commercial Heat Pumps
Geothermal heat pumps are also used in non-residential buildings, but the variety of loads and load patterns in these applications make it difficult to specify rules of thumb for capacity per unit of building area, or quantity of heat exchanger required per unit of heat pump capacity. In commercial applications a field of bore holes is drilled. Bore holes are spaced 15-20 feet apart and generally at 150-200 feet deep per ton of cooling.
The DTI's Low Carbon Buildings Programme provides grants for microgeneration technologies for householders, community organisations, schools, the public sector and businesses. The programme is managed by the Energy Saving Trust.
Under the LCBP a grant of up to £1,200 is available for domestic systems, and up to 50% for installations made under the Community stream (with a maximum of £30,000). Please refer to our Grants page for details of how to apply for grants, and of energy efficiency measures that must be in place before the grant can be accessed.