What is a heat pump?
A heat pump is a system that takes heat from a low-temperature source, such as outside air, the ground or water, and uses electricity to raise it to a higher temperature to heat a building and produce hot water. It works like a fridge in reverse: a refrigerant evaporates at low temperature, a compressor raises its pressure and temperature, and a heat exchanger passes the heat to the heating water.
Efficiency: COP and SCOP
The COP (coefficient of performance) is the kWh of heat delivered per kWh of electricity. A COP of 4 means 4 kWh of heat from 1 kWh of electricity. The SCOP is the average over a whole heating season and is more meaningful in practice. Efficiency rises as the temperature difference between source and emitters falls: a low flow temperature and a warm source (the ground) give the best results.
Types
- Air-to-water: extracts heat from outdoor air with an outdoor unit. The most common type.
- Ground-to-water: extracts heat from the ground via a borehole or ground loop; higher, steadier efficiency, but more expensive.
- Hybrid: a heat pump working alongside a boiler, which covers peaks in very cold weather.
- Exhaust air heat pump: recovers heat from extracted ventilation air.
Tips
- Have a heat loss calculation done before choosing the output.
- Aim for low flow temperatures: underfloor heating or larger radiators.
- Insulate first: lower heat loss means a smaller, more efficient unit.
- Balance the heating system properly.
- Site the outdoor unit carefully: consider noise towards neighbours and bedrooms, and drainage of condensate.
- Check grants: schemes exist in many countries, such as the Boiler Upgrade Scheme in England and Wales; check current conditions before ordering.
Related terms
- Underfloor heating
- Low-temperature heating
- Ground heat exchanger
- Ground source energy
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