With the UK government launching a number of incentives to improve the energy efficiency of your homes, air and ground source heat pumps are an ideal solution to reduce a property’s carbon footprint.
A heat pump takes the available heat from the ground or air surrounding a property and increases it to a more useful temperature for use in the home. This renewable source of heat can be used to create warm air or water (for space and central heating) as well as hot water (for both central heating and domestic hot water supply). It achieves this by taking the same principle that allows a fridge to cool your groceries and by utilizing it in reverse.
A heat pump operates in the following way:
The source of heat, which can be outside air or water which is contained within ground collectors, is either blown or pumped over the heat exchange surface of the outside part of the heat pump. This heat (although cold in comparison to a home’s internal air) is warm enough to cause the special refrigerant liquid to evaporate and turn into a gas. This gas is then put through a compressor which causes its temperature to rise. The heated gas is passed over the internal heat exchange surface. This heat can then be either blown around a property or be transferred into a home’s central heating or hot water system. The gas falls in temperature as the heat is transferred into the home and subsequently returns to a liquid state. The refrigerant returns to the outside heat exchange surface and the process repeats itself until sufficient heat is passed into the home.
How much do they cost and how efficient are they?
Air source heat pumps are about 500% efficient and some have the advantage of providing cooling in the summer. An air source pump is an alternative way to heat your home. It will enable you to generate your own renewable heat and potentially save money on your energy bills while reducing your carbon footprint.
An air-to-water heat pump typically costs between £8,000 and £18,000 for a typical detached dwelling. The costs vary depending on the size of the property, the size of the heat pump, the complexity of the system and whether you choose simple or advanced controls (for example a weather-compensated thermostat). You may also need to allow for the cost of upgrading your radiators or installing under floor heating because air sourced heat pumps tend to run at a lower temperature than typical domestic heating systems. This can cost several thousand pounds.
However Daikin now have a high temperature heat pump which can achieve 70 degrees flow line temperatures which removes the requirement to upgrade radiators. Both high and low temperature heat pumps also have the advantage of providing cooling via a reversible indoor unit (Hydro-box) which can be used to direct cooled water to heat pump convectors or fan coil units.
Ground source heat pumps are up to 400% efficient and can provide low cost, low carbon, heating and hot water and can be used with under floor heating systems. Ground source heat pumps are generally more expensive due to the complexity of the installation.
The cost of a ground sourced heat pump can vary between £13,000 - £35,000 depending on the size of the property, the type of collection system and the complexity of the system. There are two types of ground source heat pumps - one having a horizontal underground collection system buried in trenches 1200 mm underground, and one using boreholes which can be anything from 80 – 140 metres deep. You would need to allow an area in your garden of about five times the floor area of your house for a horizontal collector system. For a borehole system you should allow roughly one borehole for every 50 square metres of floor space. A horizontal system tends to be significantly cheaper than boreholes.
Ground source heat pumps can help you save between £800 and £1500 per year on your heating bill when replacing an old electric system (not a gas fired system). However the payback period is difficult to predict. This is because it depends on how efficiently your system works, the type of system you're replacing and how well your home is insulated. If you’re replacing an average gas fired heating system, a ground source heat pump is unlikely to save much on your annual bill in comparison but it improves your carbon footprint.
Despite the high installation cost compared to conventional heating systems, the Renewable Heat Incentive payments in the UK will help to offset the impact of the high initial price and reduce the running costs of the heat pump. The RHI payments are earned over the first seven years in the case of domestic systems. Currently the RHI tariff for a ground sourced heat pump is 21.92 pence per kilowatt hour (see Grants below)