A few metres underground the earth remains at a constant temperature, in the UK this is somewhere between 10 – 15 degrees. The latent heat can be transferred into a house using a ground source heat pump. Heat pumps draw heat from the ground via a ground collector (slinky) or a ground probe (bore hole).
A 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 which will cool the interior in hot weather acting as an air conditioner.
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.
Both these systems require power to drive them, but in an efficient system, one kilowatt of energy can generate three kilowatts of heat. 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 and above.
TYPICAL GROUND OR AIR SOURCE SYSTEMS COST FROM £7,000 - £11,000, EXCLUDING THE INDOOR DISTRIBUTION SYSTEM TO BE USED HOWEVER GRANTS ARE AVAILABLE.
Although the installation of a ground source heat pump to an existing building can be disruptive and relatively costly, there are significant advantages in terms of operating costs, maintenance and durability. There are however important considerations to take into account as to whether ground or air source heating is suitable for a project such as outdoor space, ground constitution, the heat distribution system to be used and what kind of fuel is being replaced. The payback is greater if the system is replacing electricity, oil, LPG or coal but is not so high for gas.
Typical ground or air source systems cost from £7,000 - £11,000, excluding the indoor distribution system to be used however grants are available. These costs will reduce if the project is a new build and installation works can be combined with construction. Properties can save from £400-£800 per year and from 2-8 tonnes of C02 depending on the fuel the system replaces.
