Ground source heat pumps

Ground source heat pumps use pipes buried in the garden to extract heat from the ground. Usually the heat extracted is then used to heat radiators, underfloor heating systems and hot water.

How do they work?

In the UK just below the surface, the ground stays at a fairly constant temperature, enabling a ground source heat pump to be used throughout the year - even in the middle of winter.

The ground source heat pump circulates a mixture of water and antifreeze around a number of coils of pipe, called a ground loop, or a length of pipe placed in a borehole, 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. Lower temperature heat passes through the heat pump compressor and is concentrated into a higher temperature heat capable of heating water for the heating and hot water circuits of the house.  The ground loop fluid, which has now cooled, passes back into the ground where it absorbs further energy from the ground in a continuous process.

The length of the ground loop depends on the size of the property and the amount of heat required.  The longer the loop, the more heat can be drawn from the ground.  The size of the loop however, also depends on the amount of space available.

It is common practice to install the ground loop coiled in trenches about two metres deep, but if there is not enough space in the garden these can be installed in the form of a vertical loop bored down into the ground.  This would be of a depth of up to 100 metres for a typical domestic home.

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.
• Can provide space heating and hot water.
• Can lower fuel bills, especially if you are currently using conventional electric heating.
• Little or no maintenance with the ,fit and forget, classification.

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 a number of factors, some of which are outlined below.

• 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.