Will Swan from The University of Salford describes the development of the Energy House 2.0 project to test two new build models by Barratt and Bellway, and compare different approaches to meeting the Future Homes Standard affordably.
The Future Homes Standard provides far more rigorous performance demands as applied to new build homes than currently. The uplift to a 75% reduction from Part L (2013), increases in airtightness, and a required understanding of overheating risk requires the industry to take a more technical approach than in previous iterations of the regulations. For many, particularly volume developers, this potentially means a tipping point away from traditionally built homes, with new fabric technologies, heating systems and controls regimes required to meet the standard. While product manufacturers have traditionally invested in research and development, the key points of failure are often around integration issues, such as construction, installation and commissioning. These more stringent demands, focused on the performance of the building, requires the sector as a whole to consider how they might deliver homes when the regulations come into force in 2025.
The University of Salford completed the construction of Energy House 2.0 in 2022 and this provided a perfect opportunity for the industry to explore what the Future Homes Standard meant for the sector. Energy House 2.0 is a large environmental chamber, large enough to allow whole houses to be tested under controlled conditions. The conditions under control are temperature (-20˚C – 40˚C) and relative humidity, while large-scale rigs provide snow, wind, rain, and solar gain. This was built on the work of the Salford Energy House, constructed in 2011. This was a Victorian end-terrace built within an environmental chamber to address the retrofit challenge. The testing of whole buildings under controlled conditions remains unique to Salford in the UK, and has not been replicated globally on this scale.
The development of the facility, the changes in the regulations and the industry drive to deliver created a unique set of circumstances that led to the development of a cutting-edge project to explore the future of UK housing.
Energy House 2.0
In 2011 the original Salford Energy House, now called Energy House 1, was developed to look at retrofit. It is a Victorian property, selected as it represented 20% of the UK housing stock by typology, as well as being the most problematic to retrofit, often called “hard to treat”. The facility represented a major change in how we could understand the impact of different interventions, focussing on manufacturers of all sizes, ranging from major international companies, such as Saint Gobain, to innovative new start-ups.
This approach gave advantages over the existing methods for understanding products. The existing methods were one of two approaches. The first is a bench test; these are individual products such as boilers or insulation, tested in isolation for their performance. The weakness with this approach is that it did not take into consideration interactions with the environment, other elements of the building, or the risks associated with installation or commissioning. The second existing approach was the field trial. These are often complex and, by necessity, large-scale. Typically, 100 occupied homes will be monitored for two heating seasons, usually between October and March. They can suffer from occupants withdrawing from studies, data loss on multiple sets of equipment, and unpredictability around construction times and weather. They are lengthy and costly, and this can provide difficulties for innovators who need to understand if their product is performing more quickly than a robust study will allow.
The approach taken at Salford Energy House has a number of advantages over the existing approaches. Firstly, repeatable experiments can be conducted. Simply, the house may be tested without an intervention, the intervention is made, and the house can be tested under exactly the same conditions, giving a clear measurable impact of the intervention. An excellent example of this is the boiler turn down project undertaken with the National Endowment for Science Technology and the Arts, which ultimately became UK Government advice during the cost-of-living crisis. The impact on energy consumption and comfort was analysed under different boiler flow temperatures under identical conditions, something not possible in the field.
Secondly, the data provided by an experimental house is in far more detail than is possible in the field. Salford Energy House has more than 200 fixed sensors and more can be added, giving a high-level of understanding on not only whether a product performs, but also providing enough detail to understand why or, perhaps more usefully, why not. Finally, as the house is unoccupied, it can be changed and adapted with the needs of the project without inconvenience for the occupant. The approach does not replace the existing approach, both field trials and bench tests are still very much part of understanding building performance. However, more than a decade of work shows us the approach has considerable power in quickly assessing the impact of retrofit improvements.
Energy House 2.0 was conceived in light of the limitations of the Salford Energy House. The team at Energy House Labs at the University of Salford recognised that the single building archetype limited the type of work we wanted to do. Additionally, the temperature ranges and weather replication needed to better reflect an international range. Finally, the team wanted a facility that would retain leadership in the approach. The Energy House 2.0 concept was developed over a two-year period from 2016, with funding from the European Regional Development Fund (£8.35m), the Office for Students, and the University of Salford contributing to this £16.5m project. As part of the launch in January 2023 the team ran a competition to identify projects that could be constructed in the two environmental chambers. In response to the emerging Future Homes Standard, two properties were put forward from the UK new build sector, Barratt and Saint Gobain, and a property from Bellway.
About the Properties
eHome2 and The Future Home (TFH) were built within the chambers exactly as they would be built onsite. The scale of the chambers allowed lifting and ground working equipment to be brought indoors. The design principles of both homes were to ensure that multiple configurations of the homes could be tested. This meant that fabric systems and control changes could be switched between or entirely replaced, as the teams and their supply chains explored issues such as performance, cost, and buildability.
eHome2 developed by Saint Gobain and Barratt is an adaptation of the existing Moresby House type. The construction is a closed panel timber frame, built using a new product from Saint Gobain. It is heated by a Vaillant heat pump, via Thermaskirt perimeter heating emitters at skirting board level, as well as having an infrared heating system that can be used independently to allow a comparison between them. Ventilation is provided by two systems which can be switched easily.
A whole house MVHR system is provided alongside a dMEV system, this allows for both systems suggested by the Future Homes Standard consultation to be examined. Domestic hot water is supplied from the Vaillant heat pump system through to a cylinder. In addition, an air source heat pump hot water cylinder is also installed, which is required to deliver hot water when the infrared heating is being used.
The Future Home, designed by Bellway, has a timber frame with a more traditional wall build up delivered using an open panel timber frame product, with PIR infill, a cavity and an external brickwork skin. The property has multiple heating systems including two different air source heat pumps – a Panasonic mono-block unit and a roof mounted Worcester Bosch Hydrotop.
These can feed two separate heating emitter types – wall mounted radiators and a ground floor underfloor heating system, as well as two independent infrared heating systems. The domestic hot water is fed by the Panasonic ASHP. This house also has two switchable ventilation systems; MVHR and dMEV.
Research commenced in May 2023 with a detailed programme that included not only the lead partners, but also their supply chain, as well as innovators new to the sector. The project was supported with a £2.3m UK Research and Innovation Grant, which began in June 2023 and lasts two years. This allowed the team to not only look at energy performance, but widen the performance issues to include acoustics and air quality.
Current & Future Tests
The research was conducted at two levels. The first level aimed to measure the overall fabric performance of the entire house to determine if it performs as intended. The second level aimed to measure the performance of individual elements of the house’s fabric to understand their specific contribution to the overall performance. In December 2023, the Future Homes Standard consultation was released. The table on the facing page provides an overview as how eHome2 and Future Home performed against the proposed standard for each of the individual elements.
Key Learnings
Each home had its combined heat loss measured using the ‘coheating’ test method. Detailed information, including all analyses, can be found in the final reports (see QR codes on page 46). Previous research identified significant issues with the performance gap in new homes built in the UK. A study by Leeds Beckett University (LBU) revealed fabric performance gaps ranging from 5% to 140% in a sample of 30 new homes (see graph above). TFH showed a performance gap of 7.7%, while eHome2 had a gap of 3.9%. The Energy House 2.0 test homes’ results are marked in orange, indicating both homes had a low performance gap when compared with existing homes.
Air Tightness
TFH’s air tightness was tested using two methods: the blower door method and the Pulse test. There was a difference between the design value and the measured value. The design value was 2.5 m³/h/m², but the measured result was 4 m³/h/m². This is a difference of 1.5 m³/h/m², which is 61% worse than the design value. Thermal imaging and visual inspections identified that extra sockets and service penetrations drove much of this gap. However, this was due to the experimental nature of the house, with multiple heating systems installed to allow side-by-side comparison.
eHome2’s air tightness was tested using two methods: the blower door method and the Pulse test. There was a difference between the design value and the measured value. The design value was 3.0 m³/h/m², but the measured result was 2.8 m³/h/m². This is a difference of 0.2 m³/h/m², which is 6.2% better than the design value.
Whole House Heat Loss
eHome2 was designed to have a Whole House Heat Loss (Heat Transfer Coefficient or HTC) of 73.8 W/K, based on the SAP energy model. This includes both the heat loss through the building’s materials and the heat loss due to air leakage. When measured using the coheating method, the HTC was 76.7 (±2.1) W/K. This shows a difference of 2.9 W/K, or 3.9%, which is higher than the margin of error, indicating a small performance gap. Measurements for eHome2 were taken using the Saint-Gobain QUB and Veritherm test methods. Representatives from Veritherm and QUB conducted these tests independently of the research team. The tests were done under the same conditions as the coheating method, with the chamber set to 5°C, to allow for direct comparison.
TFH was designed to have a Whole House Heat Loss (Heat Transfer Coefficient or HTC) of 76.3 W/K, based on the SAP energy model. This includes both the heat loss through the building’s materials and from air leakage. When measured using the coheating method, the HTC was 82.1 (±1.8) W/K. This shows a difference of 5.9 W/K, or 7.7%, which is higher than the margin of error, indicating a minor performance gap. HTC measurements were taken using the Saint-Gobain QUB and Veritherm test methods. Representatives from Veritherm and QUB conducted these tests independently of the research team. The tests were performed under the same conditions as the coheating method, with the chamber set to 5°C, to allow for direct comparison.
Both properties had a small performance gap that, potentially, would not be measurable in the field due to higher levels of uncertainty, indicating an overall high level of performance against design intent. However, the study created an opportunity to undertake a detailed building pathology study.
In eHome2 there were some small areas of insulation in the prototype timber frame wall panel where the insulation had become compressed during the manufacturing process, allowing some air movement within the panel. This finding allowed the team to design additional research and create a test cell to evaluate future iterations of the panels.
The Future Home, as outlined above, had a performance gap that was mainly driven by issues of airtightness due to factors related to the experimental nature of the property, some of which could have been contributed to by the large number of heating systems and service penetrations. In addition, the uneven application of loft insulation meant the roof of the property underperformed by 56%.
Technical Learnings
As important as the technical learnings are on this project, one of the key takeaways that the team has learnt is how the sector can work with the research sector and each other, and in a more open way. The partners shared research resources and data and have committed to making the data available for the wider sector, including issues and difficulties, which we have highlighted above. Net zero and energy efficiency are UK problems, and this approach means that the investments made by all parties are shared with industry in order to help drive change.
The work will continue into 2025 with the next stage of testing, due for release shortly, focusing on the performance of the heating systems under controlled conditions. This will focus on the comparison of heating systems in terms of energy usage, running costs, carbon and thermal comfort. This will cover a number of different configurations of air source heat pumps, emitter types, as well as infrared heating. These reports are expected to be available in late summer 2024.
Energy House 2.0 is still a relatively new facility, having only been launched 18 months ago. We can see the value in being able to understand buildings in this level of detail. There are opportunities to understand a wide range of topics including better understanding occupants, as the facility is designed to safely allow people to live in these homes.
The opportunities for this and other built environment research are being explored as we work with new partners, covering new areas such as digital energy, electric vehicles, new materials and circular economy.
Will Swan is director of Energy House Laboratories at the University of Salford