ShareHeat pump efficiency at low temperatures
A study based on field data shows that heat pumps had significantly higher energy efficiency than oil or gas heating systems, particularly for outdoor temperatures above -10°C.
Heat pumps have become a key tool in the global transition to clean, reliable energy and have been identified as the priority future heating technology in many net-zero emission scenarios, such as the European Green Deal.
A frequently asked question is how well air-source heat pumps perform at low temperatures. The temperature difference between the source (outside air) and the sink (the place of heat supply) of a heat pump plays a determining role in the Coefficient of Performance (COP) and therefore in its overall performance. If the source temperature drops and the sink temperature remains constant, the COP drops. In case of outdoor temperatures below 0°C, air-source heat pumps may also experience a reduction in their COP due to the need for defrosting of external components.
In a recent article (1), researchers from the University of Oxford analysed field data relating to the performance of air-source heat pumps. Based on data from North America, Asia and Europe, they found that heat pumps were two to three times more efficient than oil and gas heating systems in homes and offices at temperatures between 0°C and approximately -15°C. At temperatures approaching -30°C, heat pumps still had a significant advantage, with efficiencies around 1.5 times higher than oil and gas heating systems.
While most European countries experience winters with minimum temperatures above -10°C, the analysis suggests that heat pumps can be successfully used in these conditions without the particular need for auxiliary heating. However, this requires careful design of the heating system and high-quality installation.
For climates with temperatures below -10°C, given the corresponding increase in demand heating and the reduction in the efficiency of the appliance, additional heating may be necessary.
The authors conclude that widespread deployment of air-source heat pumps can contribute to decarbonisation goals for building heating in most European countries. Geothermal heat pumps and air-source hybrid systems can be an attractive solution in colder climates.
Sources:
(1) D. Gibb et al. Coming in from the cold: Heat pump efficiency at low temperatures, Joule (2023) https://dx.doi.org/10.1016/j.joule.2023.08.005