Ground source heat pumps - Introduction

05/06/2009 by David Slade.

Heat water for your home with pipes buried in the garden

Ground source heat pumps use pipes buried in the garden to extract heat from the ground. This is usually used to warm water for radiators or underfloor heating systems. It can also be used to pre-heat water before it goes into a more conventional boiler.

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

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. When the liquid travels around the loop it absorbs heat from the ground - used to heat radiators, underfloor heating systems and even hot water.

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.

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 to a depth of up to 100 metres.

The efficiency of a ground source heat pump is measured by a coefficient of performance (CoP) - the amount of heat it produces compared to the amount of electricity needed to run it. A typical CoP for a ground source heat pump is around 3.2.

Ground source heat pumps

The benefits of ground source heat pumps

• Reduce your CO₂ emissions: a typical ground source heat pump saves around 1.8 tonnes of carbon dioxide every year when replacing oil.

• Eliminate your fuel bills: ground source heat pumps run on electricity, so there’s no need to pay for gas, oil or solid fuels to heat your home.

• Cut down on wasted electricity: heating your home with a ground source heat pump is much more efficient than using electric radiators.

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, oil, Liquid Petroleum Gas (LPG) or coal heating system, a ground source heating system will pay for itself quite quickly. If you’re replacing a more efficient gas heating system, your savings will be smaller.

• What type of heating system do you want? Underfloor heating systems or warm air heating will work much better than radiator-based systems.

• Is the system intended for a new development? Combining the installation with other building work can reduce the cost of installing the system.

Costs and savings

Costs for installing a typical system suitable for a detached home range from about £6,000 to £12,000. Running costs (to produce heating and 50% of domestic hot water) are likely to be around £540 per year, but will depend on a number of factors - including the size of your home and how well insulated it is.

Savings can be considerable - up to 1.8 tonnes of CO2 and £750 if you’re replacing an oil-fired central heating system.

To reduce your home’s CO2 emissions further, consider installing solar electricity or some other form of renewable electricity generating system to power the compressor and pump.

Savings above assume ground source heat pump installed in a detached property and provides up to 50% of domestic hot water as well as 100% of space heating.

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 or in the roof space 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.

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