Energy Systems Catapult has published interim data on field monitoring of air source heat pumps in the UK between November 2020 and August 2022. The figures show that heat pumps are three times more efficient than Gas boilers and that their average coefficient of performance (COP) on cold days is 2.44 compared to 2.80 all year round.
“With the release of this data, we can finally put to bed the notion that heat pumps don’t work in cold conditions and are inefficient to use,” said Marc Brown, interim business director of Energy Systems Catapult. “We have found the exact opposite. They are three times more efficient than Gas boilers and work in cold conditions.
The project is funded by the UK Department of Energy Security and Net Zero, which commissioned the Energy Systems Catapult, a not-for-profit net zero innovation centre, to report on the data. A total of 742 air source heat pumps were installed in detached houses, semi-detached houses, townhouses and apartment buildings. The age of the properties extends from before 1919 to 2001 and later.
The heat pumps have been installed by three delivery contractors – Warmworks, E.ON and OVO Energy. Their performance was monitored from November 2020 to August 2022, with Seasonal Performance Factors (SPF) indicating their effectiveness in situ over a 12-month period. The results show that the median SPF value is 2.80 for heat pump types, modes of operation and home types.
“This is a significant increase of around 0.3-0.4 (from 30% to 40% of the Renewable Heat Premium Payment (RHPP)) since the heat pump trial in 2011-14,” Energy Systems Catapult said in a statement, referring to the UK government’s introduction of incentive system. “Innovations in the industry and in the heat pump systems themselves are likely to be the leading factor in this performance improvement.”
The figures also show considerable variation in performance across heat pump models, with refrigerant and supply water temperatures being key culprits. Heat pumps using R32 refrigerant had a median SPF of 2.94, followed by propane (R290) at 2.89 and R410a at 2.66. Their global warming potential (GWP) is 675, 3 and 2,088.
In terms of service water temperature, the data shows that heat pumps that can reach temperatures above 65 C have a median SPF of 2.89 to 2.92, while low service temperature heat pumps have a median SPF of 2.74 to 2.94. However, the report says that “use above 65 C is not a common phenomenon, with 81 out of 94 heat pumps operating at a flow temperature above 65 C less than 1% of the time.”
The project also analyzed the performance of the heat pump on the coldest days of the year in Great Britain, when the average outside temperature varied from -5.8 C to 2 C. Their coefficient of performance (COP) was calculated for each cold day with an average of 2.44.
“This result shows that heat pumps continue to operate at high efficiency – providing needed heat to homes – across a wide range of property types, even in cold conditions,” Energy Systems Catapult said.
Brown concluded that heat pumps have been proven to work.
“Great Britain is heat pump ready. Now we need to apply these lessons,” concluded Brown. “Government and industry should commit to investing in upskilling existing installers of low-carbon heating solutions and doing more to attract new talent to the industry.”
