Air Source Heat Pumps
Air source heat pumps are used to provide heat and hot water for dwellings. They run on electricity, but are incredibly efficient (in some cases 300% or more), which means that for every one unit of electricity used, they produce 3 units of useful heat.
If you compare that to a brand new boiler which is 90% efficient (1 unit of gas produces 0.9 units of useful heat), you can quickly see why these systems are so popular. In fact, if you don’t have access to mains gas, heat pumps are definitely the way to go to fulfil your heating and hot water requirements – provided you have a well insulated home.
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The air source heat pump needs to be located outside in the open air, and uses a fan to draw air into it. This air then flows over a heat exchanger, which contains a refrigerant liquid. An evaporator uses the latent heat from the air to heat the refrigerant liquid sufficiently until it boils and turns to a gas. This gas is then compressed by a compressor, which causes it to significantly increase in temperature. An additional heat exchanger then removes the heat from the refrigerant (turning it back to a liquid), which can then be used as useful heat. There are two types of air source heat pump: air-to-water heat pumps and air-to-heat pumps.
Air to water heat pumps are by far the most popular – these take heat from air outside the property and transfer this to water that can be used for space heating or as hot water for washing within the property.
These remove latent heat from the air outside the property which is then simply fed into the building through fans. This type of heat pump cannot be used to produce hot water.
Since they include fans and compressors, air source heat pumps require electricity to operate, and bearing in mind the price of electricity is approximately 15p / kWh and gas is just 4p / kWh, on the face of it, you would expect heat pumps to be far more costly to run than gas boilers.
This is not the case though – since for every kW of electricity used to run them, they provide approximately 2.5-3.5kW of equivalent useful energy (depending on the model and the temperature of the external air), this makes running costs comparable to a traditional gas boiler.
Heat pumps are part of the Renewable Heat Incentive scheme recently launched by the Government. It means that you can get paid 7.3p/kW of renewable heat you generate. The RHI payment is based on the heat demand figure that comes off the EPC – but you will require a Green Deal Report to successfully apply for the Renewable Heat Incentive.
Benefits of Air Source Heat Pumps
- As the heat pump provides the hot water for heating, there are large savings to be made on fuel bills – typically an air source heat pump can deliver up to 3.5kW of useful energy for every 1kW of energy needed to run it.
- An air source heat pump can still take heat out of the air in temperatures as low as minus 20 degrees.
- By installing an air source heat pump you can reduce your carbon emissions from your heating by 50%.
- Air source heat pumps are potential income sources, if properties qualify for the government Renewable Heat Incentive (RHI) scheme. The RHI is payable on an MCS ASHP installation, carried out by an MCS Accredited Installer and the payment is backdated to include any installation installed after 15th July 2009.