Ground Source Heat Pumps

What do ground source heat pumps do?

Ground Source Heat Pumps use energy absorbed from the ground to heat and provide hot water to a property.

They do this via a system of buried pipes which extract heat from the ground around a property. This is used to heat radiators, underfloor heating systems and water.

Ground source heat pumps can be used throughout the year, because the temperature remains fairly constant below the surface whatever the season.

How does a ground source heat pump work?

Energy is absorbed from the earth using a mix of water and antifreeze circulating inside a loop of pipe - known as a ground loop - buried in the garden. This is then pumped through a heat exchanger inside the heat pump.

The captured low-grade heat passes through a compressor in the pump which raises its temperature to a level capable of heating water for central or underfloor heating and hot water circuits. The ground loop fluid, which cools down in this process, is returned to the ground to absorb further energy. The process continues as long as heating is required.

Ground loop lengths can be varied according to the size of the property and the volume of heat wanted. Higher demand means that longer loops are needed, although the increased size of course requires more ground space.

Ground loops can be laid vertically or horizontally. The most common practice is a 2-metre deep trench, with the loops laid either flat or coiled at the bottom. Vertical loops can be inserted into the ground up to 100 metres deep for a typical domestic home.

As the heat pumps run on electricity, there is some impact on the environment, but the advantage is that heat they extract from the ground, air, or water is constantly and naturally renewed.

Unlike traditional boilers, fuelled by gas or oil, these ground pumps deliver heat at lower temperatures over much longer periods. This means that during colder spells they may need to be left on 24 hours, 7 days a week in order to heat a property efficiently. It also means that radiator surface temperatures should not be as high as they would when attached to a traditional system.

What are the benefits of ground source heat pumps?

  • Reduced fuel bills, particularly in comparison to, for example, electrically-heated premises
  • Smaller carbon footprint. Heat pumps can have lower carbon emissions than the fuel used by many more conventional systems
  • No fuel purchases and deliveries needed
  • Able to provide both general heating and hot water
  • Reduced maintenance requirement

Is a ground source heat pump suitable for you?

Here are a few key questions to consider:

Is there enough ground to take a suitable ground loop?
Large areas are not necessary, as there is always the vertical option. However the ground does need to be suitable for digging the trench or borehole, with good access for heavy plant machinery and possible spoil removal.

Is the property well insulated?
Ground source heat pumps produce heat at a lower temperature than traditional boilers. For this type of system to be effective it is essential that the property should be well insulated and draught-proofed.

What fuel is currently being used?
A ground source system will pay for itself in a much shorter time span if it is replacing an electric or coal heating system. (Heat pumps are not advised for homes served by the gas network.)

What type of heating system is planned?
Ground source heat pumps work better with underfloor or warm air heating than with radiator-based systems, which require higher water temperatures.

Is the system intended for a new development?
The cost can be reduced by installing it in conjunction with other building works.

What are the Costs and Savings?

Costs
A typical system cost, say for a detached domestic property, will range from around £9,000 to £17,000.

The cost of running the system will depend upon a range of factors, including the size of the property and the level of insulation.

Savings:
These will depend on several factors, including those detailed below.

It is important that the system is appropriately controlled for the demands being placed on it. Actual savings figures will always depend on relevant exact fuel prices

Heat distribution method: 
According to our research many experts favour underfloor heating to provide a more efficient solution than radiators. As previously stated, this is because the water does not need to reach such a high temperature. Where underfloor heating is not an option, then radiators should be as large as possible. Advice can be sought from the installer.

Fuel costs: 
Using a ground source heat pump does not mean an end to fuel bills, because the pumps are powered by electricity. Any savings will be affected by the price of your previous fuel as well as the price of the electricity needed to run the devices.

Old and new system efficiency: 
The efficiency of your old heating system will have dictated its running costs. The difference between running the heat pumps and an inefficient older system will be greater, giving bigger savings.

Hot water: 
If the purpose of either the new or old system is supply hot water as well as heating, running costs will be higher. When preparing a comparison make sure they are like for like.

Temperature setting: 
If you use the heat pumps to increase the ambient temperature of your building from previous levels with your old heating system then you can expect your heating bills to be higher and no savings to be made. 18 to 21 degrees Celsius is the optimum setting for your thermostat.

Using the controls: 
Efficient and effective control of the system is the only way to get the most out of it. Ask your chosen installer to explain in detail how to control the system for maximum efficiency.

Want to know more?

To find renewable technologies to suit your property, try the Energy Saving Trust energy selector tool at. http://www.energysavingtrust.org.uk/renewableselector/start/

Curious about the Technologies?

For more information on home energy generation technologies, contact your local Energy Saving Trust Advice Centre on 0800 512 012.

For specific technology questions, visit the Heat Pump Association at http://www.feta.co.uk/hpa/