Air Source Heat Pumps (ASHP)
Air source heat pumps heat buildings by absorbing heat from the outside. Air-to-air systems provide warm air which is circulated to heat the building, while air-to-water systems heat water to provide heating through radiators or an underfloor system.
Air source heat pumps work in the same way as a fridge that uses refrigerant to extract heat from the inside and expel it to the outside, but in reverse.
An air-source heat pump has three main parts:
- an evaporator coil that absorbs heat from the outside air
- a compressor that pumps the refrigerant through the heat pump and compresses a gaseous refrigerant to the temperature needed for the heat distribution circuit
- a heat exchanger that transfers heat from the refrigerant to air or water
Due to the low temperature output of ASHPs (typically 35-45 degrees C) underfloor heating is the most effective interface. ASHP is essentially an efficient form of electric heating. It does not provide substantial CO2 savings if compared to natural gas heating and should therefore only be considered in off-gas locations. Its seasonal matching with heat demand is not good as it performs worst when heating is most required. Its efficiency is lower than that of ground source heat pumps.
Summary
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Extracts energy from the air using technology similar to refrigeration. Low temperature heat (35 - 50 degrees C) is produced and can be used for space heating and potentially for hot water
- Should only be used in off-gas locations
- Constraints: air temperatures, output temperatures, low carbon saving potential
- Advantages: simple installation
- Typical lifespan of 15 years
- Only in off-gas location
Examples
- Health Centre Case Study - Family Cancer Information & Support Centre, Norwich. Click here to view.
Links
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Heat Pump Association (HPA)
- EST introduction to ASHP. To view click here.
