Ground source heat pumps

Ground source heat pumps use pipes buried in the garden to extract heat from the ground. This is usually used to heat radiators or underfloor heating systems and hot water.

Beneath the surface, the ground stays at a fairly constant temperature, so a ground source heat pump can be used throughout the year - even in the middle of winter.

• How do ground source heat pumps work?
• The benefits of ground source heat pumps.
• Is a ground source heat pump suitable for my home?
• Costs and savings.
• Air and water source heat pumps.
• Find out more.

How does a ground source heat pump work?

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 the garden. Heat from the ground is absorbed into this fluid and is pumped through a heat

exchanger in the heat pump. Low grade heat passes through the heat pump compressor and is concentrated into a higher temperature useful heat capable of heating water for the heating and hot water circuits of the house. Ground loop fluid, now cooler, passes back into the ground where it absorbs further energy from the ground in a continuous process while heating is required.

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.

Normally the loop is laid flat, or coiled in trenches about two metres deep, but if there is not enough space in your garden you can install a vertical loop down into the ground to a depth of up to 100 metres for a typical domestic home.

Heat pumps have some impact on the environment as they need electricity to run, but the heat they extract from the ground, air, or water is constantly being renewed naturally.

Unlike gas or oil boilers, heat pumps deliver heat at lower temperatures over much longer periods. This means that during the winter they may need to be left on 24/7 to heat your home efficiently. It also means that radiators should never feel as hot to the touch as they would do when using a gas or oil boiler.

Ground source heat pumps

Ground source heat pumps

The benefits of ground source heat pumps

• Can reduce your carbon footprint: heat pumps can lower your home’s carbon emissions, depending on which fuel you are replacing.
• No fuel deliveries required.
• Can provide space heating and hot water.
• Can lower fuel bills, especially if you are currently using conventional electric heating.
• It's often classed as a ‘fit and forget’ technology because it needs little maintenance.

Is a ground source heat pump suitable for my home?

To tell if a ground source heat pump is right for you, there are a few key questions to consider:

• Is your garden suitable for a ground loop? It doesn't have to be particularly large, 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 produce a lower temperature heat than traditional boilers, it's essential that your home is insulated and draught proofed well for the heating system to be effective. It could also make the system cheaper and smaller.
• What fuel will you be replacing? If you're replacing an electric, or coal heating system, a ground source heating system will save you more on your heating bills. Heat pumps are not recommended for homes on the gas network.
• What type of heating system will you use? Underfloor heating systems, larger radiators or low temperature fan convectors (warm air heating) can perform better than standard 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.
• Use the Home Energy Generation Selector tool to find out if a heat pump is suitable for your home.

Costs and savings

Costs of installing a typical system range from about £7,000 to £13,000. Running costs will depend on a number of factors - including the size of your home and how well insulated it is.

Savings - will vary depending on many factors, some are outlined below. It is important that the system is controlled appropriately for your needs.

• The heat distribution system: If you have the opportunity, underfloor heating often provides greater efficiencies than radiators because the water doesn’t need to be heated to such a high temperature. If underfloor heating isn’t possible, then use the largest radiators you can.
• Fuel costs: you will still have to pay fuel bills with a heat pump because they are powered by electricity. The saving you achieve can be affected by the price of the fuel you are replacing and the price of the electricity for the heat pump.
• Efficiency of old and new system: the efficiency of the old heating system will affect how much you spent on heating bills previously. If the old heating system was inefficient heating bills could have been high and the difference between the new running costs and the old running costs will be greater, therefore providing a greater saving.
• If the system is providing hot water as well as space heating: the provision of hot water can lower system efficiencies, therefore making running costs higher.
• Temperature setting: if you heat your home to much higher temperatures with a new heat pump system than you did with an old heating system then you will experience greater comfort benefits, but heating bills will be higher than if you continued with the same heating pattern. It’s a good idea to set thermostats to around 18 to 21 degrees centigrade.
• Using the controls: learn how to control the system so you can get the most out of it. Your installer should explain to you how to control the system so you can use it most effectively.

To reduce your home's CO2 emissions further, consider using solar water heating to provide low carbon hot water in the summer months.

The Energy Saving Trust is currently conducting field trials of ground and air source heat pumps, in order to get a better idea of how they perform, and the saving they achieve, in real life environments. Results will be published in late summer 2010.

Air and water source heat pumps

These systems use similar principles to ground source heat pumps to extract heat from air or water instead of the ground.

Air source heat pumps can be fitted outside a house and generally perform better at slightly warmer air temperatures. Water source heat pumps can be used to provide heating in homes near to rivers, streams and lakes.

The Department for Energy and Climate Change (DECC) have announced that the Renewable Heat Incentive (RHI) is expected to be launched in April 2011. It is designed to provide financial support to encourage the uptake of renewable and low carbon heat technologies like heat pumps. It is currently in a planning stage and no final decisions have yet been made by DECC.

Find out more about air source heat pumps

Find out more

What's suitable for your home?
To find renewable technologies to suit your home, try the Energy Saving Trust Home Energy Generation Selector tool.

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.