Ground and Air Heat Pumps

Ground Source Heat Pumps

The ground acts as a very large store of heat energy. Ground source heat pumps make use of this energy naturally stored in soil, bedrock and groundwater as a heat source. They do require electricity to operate, but efficiently produce up to five times as much heat energy, for every unit of electricity they use.

Ground source heat pumps use heat collecting pipes in a closed loop, containing water (with a little antifreeze) to extract this stored energy, which can then be used to provide space heating and domestic hot water. Heat pumps can also be reversed in summer to provide cooling, and is a zero carbon, energy-efficient way of heating buildings.

Heat Pump Benefits

Could lower your fuel bills, especially if you replace conventional electric heating. Further savings can be made by using an electricity tariff such as Economy 7/10 as timing the system to coincide with off-peak tariffs will enable the heat pump to work more economically.

Require less maintenance than combustion based heating systems. They also have a longer life than combustion boilers. The ground heat exchanger element of a ground source heat pump installation has a design life of over 50 years.

Could provide you with an income through the government’s Renewable Heat Incentive (RHI).

Produce no carbon emissions on site (and no carbon emissions at all, if a renewable source of electricity is used to power them).

Save space. There are no fuel storage requirements.

Can heat your home and provide hot water.

Unlike gas and oil boilers, heat pumps deliver heat at lower temperatures over much longer periods. During the winter they may need to be on constantly to heat your home efficiently. You will also notice that radiators won't feel as hot to the touch as they might do when you are using a gas or oil boiler.

Air source heat pumps are usually easier to install than ground source as they don't need any trenches or drilling, but they are often less efficient than ground source pumps. Water source heat pumps can be used to provide heating in homes near to rivers, streams and lakes.

Is a heat pump suitable for my home?

Heat pumps work best when producing heat at a lower temperature than traditional boilers. As a result they are most suitable for extremely well insulated and draught-proofed houses fitted with underfloor heating. It is possible to use a heat pump with radiators, but to get the same level of heat you will need larger radiators.

They are best installed in houses off the gas grid, or in a new build. Ground source heat pumps need plenty of outside space for the pipework, it doesn't have to be particularly big, but the ground needs to be suitable for digging a trench or a borehole. Air source heat pumps can be fitted to a wall or placed on the ground. Air source heat pumps need plenty of space around it to get a good flow of air. A sunny wall is ideal.

Heat pumps aren’t suitable for every home, and systems will pay for themselves more quickly if replacing an electricity or coal heating system. Heat pumps may not be the best option for homes using mains gas.

How do heat pumps work?

Ground Source Heat Pump

A long loop of pipe, filled with water and anti-freeze, is buried in the earth. Heat from the ground is absorbed into a liquid in the ground loop and passes through a compressor that raises it to a higher temperature, which then heats water in a buffer tank.

The heating system (ideally underfloor heating) is fed from the buffer tank. The cooled ground-loop fluid passes back into the ground where it absorbs further energy from the ground in a continuous process as long as heating is required.

The only energy used by the ground source heat pump is electricity to power the compressor and the circulation pumps which transfer heat energy from the ground into the building. A well designed ground source heat pump installation will deliver three or four times as much thermal energy (heat) as is used in electrical energy to drive the system.

Air Source Heat Pump

Air source heat pumps work in basically the same way, except the heat is extracted from the air outside your home using an evaporator coil. This looks like fans on air conditioner units and is fixed on an outside wall of the building. Water source heat pumps take their heat from a lake, river or stream.

How much do heat pumps cost and save?

The cost of ground source heat pump installations varies considerably, the Energy Saving Trust puts the price range for a ground source heat pump between £9,000 and £17,000; The Centre for Alternative Technology says around £1,000 per installed kW as a rule of thumb.

Air source heat pumps are significantly cheaper at £5,000 - £10,000.

These prices do not include the cost of installing an underfloor heating system which would be around £2,000 depending on the size of your house.

There is some help available with upfront costs of installation from the Renewable Heat Premium Payments scheme and you may be able to receive payments for the heat you generate using a heat pump through the government’s Renewable Heat Incentive. This scheme should be launched in October 2012.

If the heat pump is providing hot water then this could limit the overall efficiency. You might want to consider solar water heating to provide hot water in the summer.

The table below shows the possible savings you can make when installing a heat pump system.

Air Source Heat Pumps

Air source heat pumps can provide both heating and cooling. Extracted heat from the outside air can be used to heat radiators, underfloor heating systems, or warm air convectors and hot water in your home.

The heat pump comprises of an outdoor and indoor unit which converts heat energy in the air into heat in the home. The outdoor unit extracts the energy in the air outside the property. This heat is absorbed by refrigerant solution within the unit, turned into hot air by the indoor unit and distributed within the property.

An air source heat pump extracts heat from the outside air in the same way that a fridge extracts heat from its inside. It can get heat from the air even when the  temperature is as low as -15° C.

Do Heat Pumps require much maintenance?

Heat Pumps are often classed as a 'fit and forget' technology because it needs little maintenance. Occasionally the system will need checking by a qualified engineer but this only has to happen every 3-5 years. The system should also be purged at the same time to ensure no air is caught in the system as this will affect its efficiency.

Choosing a good heat pump installer

To get the full benefit of a heat pump installation you will need to employ someone with design and installation experience. Heat pumps may not perform well unless it is incorporated in a good design by someone who understands the needs of the building, the use to which the building is being put and the local geology. Make sure that responsibility and liability for the complete installation lies with one company, ideally with a contract to guarantee consistency in after-sales service.

Hydro Power

Hydro power uses running water to generate electricity, whether it's a small stream or a larger river. Small or micro hydroelectricity systems can produce electricity for lighting and electrical appliances in an average home.

Government Grants and Schemes

Check out grants, offers and discounts to help you pay for energy-saving measures at home. These schemes help you save money, and advise on ways to cut your energy bills.

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