background

Their relative ease of installation and lower expense has meant that air source heat pumps have been the most favoured of the available technologies.

There are two main types - an air to water system uses the heat to warm water. Typically the water will be heated to around 40°C – lower than the 60-70°C common in a standard boiler system, meaning that the system is more suited to underfloor heating systems than radiators. An air to air system produces warm air, which is circulated by fans to heat a building.

However, air source heat pumps reliance on outside air means that they are less efficient when temperatures drop below -5°C. In mild weather the CoP will be around 4, but below -5°C (23°F) the CoP can drop to below 2. To allow for seasonal variation, the average CoP for an air source heat pump is around 2.7, although new models are in development with much higher efficiencies that will help to nullify this seasonal effects. 

Air source heat pumps consist of the following major components: evaporator coil - absorbs heat from the outside air, compressor - pumps refrigerant through heat pump and compresses to required temperature for heat distribution circuit, heat exchanger - transfers heat from refrigerant to air or water for use in the building

benefits

• Well tried and cost effective method of harnessing renewable energy
• Can be used to provide both heating in winter and cooling in summer, as required
• High return of renewable energy for capital costs compared to other forms of renewable energy
• Can be used in conjunction with solar hot water systems - integrated control software prioritises solar-thermal energy, reverting to heat-pump operation if solar energy is insufficient to meet demand
• Use of electric immersion heating during cold periods (rather than over specifying the capacity of the heat pump) means the heat pump can meet around 95% of the annual heat demand, with backup heating providing remaining 5%
• While underfloor heating systems are the most efficient approach, other options include air blown heating / cooling systems and conventional (oversized) radiators that work using lower temperatures than traditional boilers
• Air-source heat pumps can be located in the roof space if required

potential savings

The economics of replacing an existing condensing oil or gas boiler with an air source heat pump system are quite dramatic. For instance, to install a new oil-fired system for a typical 4-bed house would cost around £3,700. A gas-fired system would cost around £3,350. We can install an air source heat pump system for £4,500. The extra investment of £800 (compared to oil) will deliver 9.3 MWh of renewable energy per year.

According the The Energy Saving Trust the prospective financial and carbon savings from installing an air source heat pump are as follows:

All savings are approximate and are based on an air source heat pump providing 100% of space heating in a detached property.

installation requirements

Space is required on an external wall for installation of the evaporator coil, and to house the heat pump unit that contains the compressor and heat exchanger (a unit the size of a domestic refrigerator). For most properties an air source heat pump will cover the heating requirements alone, but high levels of insulation are required and a back up heating coil should also be fitted. 

cost

 Size / specification            Guide price                       House type

 small - 5-6kW                     £4,500-£6,500                  3 bed semi-detached or detached

 medium - 8-9kW                £5,500-£7,500                  4 bed detached

 large - 12-14kW                 £6,500-£8,500                  4-5 bed detached

• Prices may vary depending on site conditions
• Prices do not include domestic plumbing or central heating systems and are for supply / installation commissioning of heat pumps only
• For older and un-insulated properties please allow for upgrading of the heat pump required or for installation of additional insulation etc to bring your house up to a more modern standard

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