The Electrification of Heat Demonstration Project, carried out by Energy Systems Catapult, is examining the technical and practical feasibility and constraints of a mass roll-out of heat pumps into British homes.

As part of the project, which is funded by the Department for Energy Security and Net Zero, 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.

Seasonal performance factors indicate the in-situ efficiency of a heat pump system over the course of 12 months. Results so far have shown that the median seasonal performance factors observed in ASHP systems during the 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 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, according to the study.

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.

The project analysed the performance of heat pumps on some of the UK’s coldest days (where mean daily temperatures fell to as low as –6°C) 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 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, the project has found. Use of these units reduces the need for deeper retrofit and provides a potential solution for less efficient homes. The data released 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.

The hybrid heat pump systems were commissioned to run ‘cost-optimally’, with the system choosing when to operate the boiler or heat pump based on which is the cheapest option at a given time. Generally, the heat pump would meet the base space heating requirements and the boiler would cover hot water production and meet peak space heating demand.

The performance data reveals that the heat pumps in hybrid systems typically met about 39% of the space heating demand. They also had a median heat pump efficiency of 2.37 (237%), which is lower than standalone ASHPs; giving an estimated overall heating system efficiency of between 1.26–1.42 (126–142%), depending on the efficiency of the boiler and the proportion of hot water demand.

Commenting on the findings of the project, Marc Brown, Business Leader – Homes, at Energy Systems Catapult, says: ‘The interim findings of the Electrification of Heat Demonstration Project highlight just how far the industry has come in innovating to improve the performance and efficiency of heat pumps. With the release of this data, we can finally put to bed the notion that heat pumps do not work in cold weather conditions and that they are inefficient to run. We’ve observed the exact opposite. They are three times more efficient than gas boilers and work in cold weather conditions. Innovation is changing the game in the heating sector.’

He concludes: ‘While we’re taking steps in the right direction, we should not grow complacent. At the risk of sounding like a broken record, innovation and training are critical to the success of a mass roll-out of heat pumps. We’ve done the hard work and demonstrated that heat pumps work – the UK is heat pump ready. Now we need to apply those learnings. Government and industry should commit to investing in upskilling existing installers in low-carbon heating solutions and doing more to attract new talent into the sector.’