Air-Source Heat Pumps - Sustainability, Efficiency, and Design Considerations

What is an air-source heat pump?

The term air-source heat pump typically refers to a hot water and heating system, alternative to the traditional gas boiler. This system draws thermal energy from the ambient air and uses it to heat the house and the domestic hot water and is technically known as an air-to-water heat pump. However, the term air-source heat pump applies to anything that sources its heat from the ambient air, regardless of whether it’s going to be used to heat water or air.

Can they be used for air conditioning?

In fact, nearly all air conditioning systems use air-source heat pump technology. Instead of taking thermal energy from the air outside the house and using it to heat the house and/or its hot water supply, it absorbs the heat from the air inside the house and heats the area outside the house, creating an internal cooling effect. The difference between this and the traditional definition of an air-source heat pump is that this is an air-to-air heat pump as opposed to air-to-water.Please bear in mind that although air-conditioning systems are recognised as air-source heat pumps by HMRC, the Energy Saving Trust and so on, they cannot be fitted under Permitted Development – this precludes any air-source heat pump that is used for cooling, and this has led to a lot of confusion about whether air-conditioning systems can be called air-source heat pumps or not.

Are they sustainable?

Air-source heat pumps are viewed as being highly sustainable, because they draw existing heat from the air, rather than burning fossil fuels to generate that heat. However, the fact remains that they are powered by electricity, so the sustainability of the heat pump is dependent on the source of electricity used to power it: in brief, an air-source heat pump is only as sustainable as its source of power, regardless of whether it’s used for heating or cooling, but it does enable people to use a more sustainable option such as powering it using solar panels, which significantly reduces carbon footprint.

Will the government pay for me to have an air-source heat pump?

The government will put £5000 towards an air-source heat pump for your home to replace an existing gas boiler as part of the Boiler Upgrade Scheme, thus working towards using renewable energy for heating. However, several conditions apply to this: you must be replacing a fossil fuel heating system in an existing building, and your property must have a valid energy performance certificate with no outstanding recommendations for loft or cavity wall insulation. This is to maximise the efficiency of the heat pump.

Are they economical?

Air-source heat pumps operate at very high efficiencies of up to 400%, which means that for every unit of electricity used, up to 4 comparable units of heat are generated – in comparison, the average gas boiler operates at around 90% efficiency which means that 0.9 comparable units of heat are generated for every unit of electricity. However, electricity is far more expensive than gas, so whether your running costs will be lower with a heat pump than a gas boiler will be dependent on the available tariffs as well as the type of heat pump and how much electricity it requires to run.

What should I consider when allowing for an air-source heat pump in my design?

Heat pumps are much larger and have a greater spatial impact than the traditional gas boiler. The design must take into account a variety of other factors too, such as external plant location, whether there will be a loss of amenity space, aesthetic impact, noise, and whether it will need planning permission. When specifying an air-source heat pump, it’s always best to consult a specialist early on in the design process to ensure the smoothest design and installation.