Ground Source Heat Pumps

Ground source heat pumps

Ground source heat pumps use a buried ground loop which transfers heat from the ground into a building to provide space heating and domestic hot water. The efficiency of a ground source heat pump system is measured by the coefficient of performance (CoP). This is the ratio of units of heat output for each unit of electricity used to drive the compressor and pump for the ground loop. Average CoP over the year, known as seasonal efficiency, is around 3-4 although some systems may produce a greater rate of efficiency. This means that for every unit of electricity used to pump the heat, 3-4 units of heat are produced, making it an efficient way of heating a building. This technology is generally 3-4 times more efficient than oil or gas.

Could a ground source heat pump work for your home?

It's worth making sure your house is suitable for a ground source heat pump by asking the following questions:

1. Is there space for a trench or bore hole to be dug just outside your home? Is the ground suitable for digging?

2. What kind of heating fuel would your ground source heat pump be replacing? If it's electricity, oil or liquid petroleum gas and you live in an area with no gas supply then the payback will be more favourable.

3. Do you want the heat pump to provide all your space heating, or will you use a back-up heating system when it gets really cold? Heat pumps are most effective at providing fairly constant low level heating.

4. Is your home still being built, or undergoing major renovations? If so, it will be cheaper to install the ground source heat pump and underfloor heating system at the construction stage rather than when construction is complete.

How does a ground source heat pump work?

A ground loop made up of lengths of pipe is buried in the ground either in a deep borehole or a long trench. The pipe is filled with a mixture of water and antifreeze fluid which is pumped round the ground loop to absorb heat from the ground.

There are two main types of ground loop:

1. A vertical ground loop is placed in boreholes.

2. A horizontal ground loop is placed in a trench, either as a track loop or spiral coil or "slinky".

The type and length of ground loop and hole you use will depend on the space available and the ground conditions.

In the same way that your fridge uses frigerant to extract the heat from inside the fridge keeping your food cool, a ground source heat pump extracts heat from the ground and uses it to heat your home and provide hot water. The pump's evaporator takes in the heat absorbed by the ground loop and a compressor gets it to the right temperature for your heating system. A condenser extracts the heat which can then be used to run your under-floor heating or radiators and in some cases your hot water. Ground source heat pumps can work with radiators but under-floor heating maybe more suitable as it works at a lower temperature.

Renewable Heat Incentive (RHI)

In March 2011, the UK Government announced the details of their Renewable Heat Incentive (RHI).

The Renewable Heat Incentive is designed to provide financial support that encourages individuals, communities and businesses to switch from using fossil fuel for heating, to renewables such as solar thermal, ground Source, air Source and wood fuel.

The Renewable Heat Premium Payment scheme has now been announced and you can now make an application. There is around £12m available to householders in Scotland, England and Wales who install from 1 August 2011.

Once customers have had an MCS accredited installation they can receive an initial payment of £1,250 from the government. Thereafter on going payments are expected to start in autumn 2012 and continue for 20 years.

Permission

Most Ground Source Heat Pump systems installations do not require planning permission, but we would advise that you check this with your local planner. Exceptions apply for listed buildings, flats, buildings in conservation areas and world heritage sites - if in doubt you should check this out in advance with your local planning department (as getting planning permission after the event can be difficult and expensive).

Choosing your ground source heat pump

When buying a ground source heat pump system for your home, you need to consider both the size of the system and the best way to distribute the heat. The size of the system will depend on your heating requirements. It is always advisable to find ways to reduce your heating needs as much as possible before you install the heat pump - for example by insulating your loft, cavity walls, floors and installing double glazing. Reducing your heating needs will enable you to install a smaller system and reduce both system costs and running costs.

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