Ground Source Heat Pumps
What is Ground Source Energy?
Ground source systems use natural heat produced from the earth to provide heat and hot water to homes in a cost efficient and environmentally friendly way.
Several metres below ground level, the earth remains at a constant temperature. In the UK, this is normally between 10 – 15 degrees Celsius. This natural renewable energy can be used as a method of heating of your home and in some cases providing hot water.
Closed circuit lengths of pipe are laid in horizontal trenches or boreholes, which have been dug to a depth of two metres below ground level. These pipes are filled with water and anti-freeze, which is then pumped around the system by a heat pump. The natural ground heat raises the temperature of the water, which is then warmed to the required level by the heat pump.
Ground Loop – comprising of underground pipes in a closed circuit, in either a vertical borehole or horizontal trench. These are filled with water and anti-freeze, which pumps around the system absorbing natural heat from the ground.
Heat Pump – Moves the fluid around the circuit and is made up of three parts – the evaporator, the compressor and the condenser. The fluid changes to gas as it heats up and later condenses to liquid as it is distributed to where it is needed.
Heat Distribution System – This is the radiators or under floor heating. For hot water supply, it is the cylinders used for water storage.
The only traditional form of energy used is electricity to power the heat pump. However, the level of thermal energy, or heat, emitted is 3 – 4 times the amount of electrical energy needed to power the pump. By using ‘green electricity’, this method of heating can be made even more environmentally friendly, as all your heating will be from sustainable sources with zero carbon emissions.
Using ground source energy as a means of home heating will be more efficient in a fully insulated building. It is better suited to heating systems that have less variation between the heat source and the heat output such as underfloor heating as this operates at a much lower temperature, usually around 30 degrees compared to radiators, which normally function at around 70 degrees.
Ordinary radiators can still be used with ground source energy heating but you may need to install larger radiators than what you already have.
For domestic hot water, the water is stored in cylinders, which can then be boosted in temperature using an immersion heater.
The heat pump unit is typically housed in a cabinet around the size of a large fridge. In fact, the whole system can be likened to the way in which a fridge works, only in reverse. A fridge takes the warm air from inside and moves it outside whereas the heat pump takes the heat stored underground and brings it inside.
Some units also have a cooling system, keeping the interior of your home cool in warm weather.
Ground source heat pump systems do not come cheap and cost around £8000 – £12000. However, with an annual saving of around £400 – £800 on heating bills, it is a good long-term investment, particularly as there are practically no maintenance costs and a life expectancy of over 50 years.
Depending on the type of fossil fuel you currently use for heating and hot water, changing to a ground source energy heating system can cut your households carbon dioxide emissions by 2 – 8 tonnes each year.