Heat pumps shown to be three times more efficient than gas boilers

• Measured real-world performance of Air Source Heat Pumps (ASHPs) has increased significantly compared to data from past field trials.
• Heat pumps performed well even on the coldest observed days, with only a relatively small reduction in performance.
• High Temperature ASHPs had comparable efficiencies to Low Temperature ASHPs, indicating that they are a viable solution to reduce home retrofit requirements.

Real world monitoring has shown that Air Source Heat Pumps (ASHPs) can operate with high efficiencies, even in cold weather conditions, according to interim heat pump performance data released as part of the Electrification of Heat Demonstration Project.

Funded by the Department for Energy Security and Net Zero (DESNZ), the Electrification of Heat Demonstration Project is working to understand the technical and practical feasibility, and constraints of a mass rollout of heat pumps into British homes.

A total of 742 heat pumps were installed by the delivery contractors – Warmworks, E.ON, and OVO Energy – into a broad spectrum of housing types and ages. These heat pumps are being monitored throughout the trial to assess their performance.

The interim data and results of this monitoring (conducted between November 2020 – August 2022) have been released by Energy Systems Catapult; the Net Zero Innovation Centre appointed to lead the management contractor consortium. The analysis within the reports – Interim Insights from Heat Pump Performance Data and Interim Heat Pump Performance Data Analysis Report – will be refreshed, and additional analysis undertaken after the completion of the projects monitoring period in Autumn 2023.

Seasonal Performance Factor (Efficiency) improvements

Seasonal Performance Factors (SPFs) indicate the in-situ efficiency of a heat pump system over the course of 12 months.

The median SPF observed in ASHP systems during the EoH Demonstration Project was 2.80 (280%)*. This is a significant increase of around 0.3 to 0.4 (30-40%) since the Renewable Heat Premium Payment scheme (RHPP) heat pump trial was undertaken between 2011-2014. Innovation in the industry and in the heat pump systems themselves is likely a leading factor in this performance improvement.

However, whilst the average performance has improved, performance variation remains high. This suggests that progress is still required to improve the consistency of heat pump design and installation to support a large-scale rollout of heat pumps in existing homes and to deliver positive environmental and consumer outcomes.

Good cold weather performance

The EoH Demonstration Project analysed the performance of heat pumps on some of the country’s coldest days (where mean daily temperatures fell to as low as -6^oC) and found only a marginal decline in whole system performance. The median ASHP system efficiency was 2.44 (or 244%) on the coldest days of the year. This result indicates that heat pumps continue to operate with high efficiency – providing the requisite heat to homes – in a wide range of property types even in cold weather conditions.

High Temperature Air Source Heat Pump performance

High Temperature ASHPs – those which can achieve flow temperatures similar to that of a gas boiler – are a viable solution for meeting the heating demand of a property. Use of High Temperature units reduces the need for deeper retrofit and provides a potential solution for less efficient homes.

The data released by Energy Systems Catapult demonstrates that the High Temperature ASHPs used in the Project have performed with similar efficiencies to Low Temperature ASHPs. Heat pumps are controlled to only demand higher temperatures when it’s colder outside. During the project, these weather compensation controls rarely demanded higher temperatures, allowing the units to maintain good heat pump efficiencies whilst keeping a wider variety of properties warm year-round.

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