ThermaSkirt takes part in Salford University’s Energy House heating system tests

The £16 million Energy House 2 in Salford University is a facility big enough for developers to build full-sized houses inside, and then control the climate around them so that their heating systems can be tested under laboratory conditions. Conditions such as rain, snow, wind and temperatures as low as -20°C can be created and maintained for defined periods to test how the different heating systems perform and determine how they will meet the requirements of the Future Homes Standard.

Background

The Future Homes Standard, due in 2025, will require newly built homes to be futureproofed with low-carbon heating systems, like heat pumps, and have excellent fabric efficiency by improving insulation and minimising heat loss, thereby reducing carbon emissions by 75-80% compared to current standards. This will contribute significantly to the UK’s net-zero goals and pave the way for new homes in the future to be comfortable and environmentally responsible.

From 2022, Part L has required all new build heating systems to operate at a boiler flow temperature of 55°C as this reduces gas consumption by up to 12%, along with the associated reduction in CO2.

A reduction in boiler flow to 55°C results in a radiator correction factor of approximately 0.5, or, in layman’s terms, roughly double the size. A further reduction to a flow temperature of 45°C requires a correction factor of approximately 0.3, which means the radiators need to increase by two thirds to compensate for the drop in output.

Testing protocol in the Energy House 2

Barratt Homes and Bellway Homes each constructed a typical detached property inside the Energy House. Both Panasonic and Vaillant air source heat pumps were tested. Bellway Homes opted for underfloor heating and radiators on the first floor. Barratt Homes chose to test ThermaSkirt on both floors, with towel radiators in bathrooms and en-suites.

The two houses were then tested at -5°C and +5°C ambient outside temperatures. This was to replicate the average winter UK temperatures (+5°C) and a more serious cold snap (-5°C). The tests included running the heat pumps on both a continuous 24-hour cycle and also a more onerous (for a heat pump) stop/start ‘SAP’ cycle over a 24-hour period. The living room was set a target temperature of 21°C, with the kitchen and bedrooms set to the current building standard design temperature of 18°C. Each room was fitted with a sophisticated series of sensors to measure room temperature and heat distribution (comfort or operative temperature).

Results

The temperature in each of the rooms was measured at one-minute intervals and the electrical consumption was measured over the testing period. The performance and running costs could then be determined for each heat emitting strategy or, indeed, a combination of systems.

It was found that at -5°C ambient outside temperature, in the intermittent (SAP) mode with two short heating cycles per day, the air source heat pump was not able to deliver the necessary heat energy rapidly enough to bring the rooms up to temperature. This was true of all the heat emitters, although the underfloor heating fared, because its high thermal mass had slower response times to both heating and cooling.

The results for the -5°C outside temperature with the air source heat pump running in continuous mode, which is the recommended set-up according to most manufacturers and installers, can be read in the report. View Report.

Conclusion

• Air source heat pumps perform best when run in continuous mode and not in intermittent mode as you would a gas boiler.
• Overzoning the controls can lead to short cycling of the air source heat pump and reduced Coefficient of Performance (CoP).
• Underfloor heating and ThermaSkirt produce the most even heating patterns.
• Radiators and ThermaSkirt have faster response times than underfloor heating.
• The thermal mass of underfloor heating can offset the impact of intermittent heating cycles, but requires a longer initial warm up period.
• ThermaSkirt has lower running costs compared to radiators only.
• Running costs of underfloor heating with radiators improved compared to radiators only.
• The larger BM3 ThermaSkirt profile is required for ground floor living spaces to achieve the 21°C set point.
• Combining underfloor heating at ground floor and ThermaSkirt at first floor would most likely provide the lowest overall running costs (this combination was not tested in this programme).

The complete test report can be viewed here: Energy House 2.0 Final Summative Assessment Report