Ground Source Heat Pump
Ground source heat pumps (GSHPs) use pipes that are buried in the garden to extract heat from the ground. This heat can then be used to heat radiators, underfloor or warm air heating systems and hot water in your home.
A ground source heat pump circulates a mixture of water and antifreeze around a loop of pipe, called a ground loop, which is buried in your garden. Heat from the ground is absorbed into the fluid and then passes through a heat exchanger into the heat pump. The ground stays at a fairly constant temperature under the surface, so the heat pump can be used throughout the year. The length of the ground loop depends on the size of your home and the amount of heat you need. Longer loops can draw more heat from the ground, but need more space to be buried in. If space is limited, a vertical borehole can be drilled instead.
The benefits of ground source heat pumps
It could lower your fuel bills, especially if you replace conventional electric heating.
It could lower home carbon emissions, depending on which fuel you are replacing.
There are no fuel deliveries needed.
It will heat your home as well as your water.
There is minimal maintenance required.
Unlike gas and oil boilers, heat pumps deliver heat at lower temperatures over much longer periods.
In winter, it may need to be on constantly to heat your home efficiently, but radiators won't feel as hot to the touch as with a gas or oil boiler.
Often they are more difficult to install than air source heat pumps, but ground source heat pumps are often more energy efficient.
How do ground source heat pumps work?
Heat from the ground is absorbed at low temperatures into a fluid inside a loop of pipe (a ground loop) buried underground. The fluid then passes through a refrigeration system that raises it to a higher temperature, which can then heat water for the heating and hot water circuits of the house.
The cooled ground-loop fluid passes back into the ground where it absorbs further energy from the ground in a continuous process as long as heating is required.
If there is enough space, the collector loop can be laid horizontally in a trench about a metre or so below ground. Where there isn’t room to do this you can drill vertical boreholes to extract heat from much further down, typically 90 – 160 metres deep.
The space you need for a horizontal loop, and the depth you need for a borehole, will depend on many factors – your heat pump installer will design the collector array based on local conditions and the heat requirements of your home.
Heat pumps have some impact on the environment as they need electricity to run, but the heat they extract from the ground, the air, or water is constantly being renewed naturally.
Installing a typical system costs around £14,000 to £19,000. Running costs will depend on a number of factors including the size of your home and how well insulated it is.
How much you can save will depend on what system you use now, as well as what you are replacing it with. Your savings will be affected by:
Your heat distribution system:
Underfloor heating can be more efficient than radiators because the water doesn’t need to be so hot. If underfloor heating isn’t possible, use the largest radiators you can. Your installer should be able to advise on this.
Your fuel costs:
You will still have to pay fuel bills with a heat pump because they are powered by electricity, but you will save on the fuel you are replacing. If the fuel you are replacing is expensive you are more likely to make a saving.
Your old heating system:
If your old heating system was inefficient, you are more likely to see lower running costs with a new heat pump.
If the heat pump is providing hot water then this could limit the overall efficiency. You might want to consider solar water heating to provide hot water in the summer and help maintain your heat pump efficiency.
Using the controls:
Learn how to control the system so you can get the most out of it. You will probably need to set the heating to come on for longer hours, but you might be able to set the thermostat lower and still feel comfortable. Your installer should explain to you how to control the system so you can use it most effectively.
You may be able to receive payments for the heat you generate using a heat pump through the UK Government’s Renewable Heat Incentive.
Things to consider
Here are a few key questions to consider to find out if a ground source heat pump is suitable for your home and needs:
- Is your garden suitable for a ground loop?
It doesn't have to be particularly big, but the ground needs to be suitable for digging a trench or a borehole and accessible to digging machinery.
- Is your home well insulated?
Since ground source heat pumps work best when producing heat at a lower temperature than traditional boilers, it's essential that your home is well insulated and draught-proofed for the heating system to be effective.
- What fuel will you be replacing?
The system will pay for itself much more quickly if it's replacing an electricity or coal heating system. Heat pumps may not be the best option for homes using mains gas.
- What type of heating system will you use?
Ground source heat pumps can perform better with underfloor heating systems or warm air heating than with radiator-based systems because of the lower water temperatures required.
- Is the system intended for a new development?
Combining the installation with other building work can reduce the cost of installing the system.
Heat pump systems typically come with a warranty of two to three years. Workmanship warranties for heat pumps can last up to 10 years, for example through QANW (Quality Assured National Warranties).
Many manufacturers also offer optional extensions of warranty for a fee.
You can expect them to operate for 20 years or more, but they do require regular scheduled maintenance.
A yearly check by you and a more detailed check by a professional installer every three to five years should be sufficient.
The installer should leave written details of any maintenance checks you should undertake to ensure everything is working properly. Consult with your supplier for exact maintenance requirements before you commit to installing a heat pump.
The Ground Source Heat Pump Association says there is no need for safety checks for ground source heat pumps and routine maintenance requirements are very low.
These may include pre-heating season checks of the water pump, external pipes and fittings and electronics.