Cambridge Consultants’ Nathan Wrench on driving carbon reduction in housing

If you knew your house was leaking energy, would you still buy it? In the UK, domestic heating accounts for about 18% of the country’s total CO2 emissions, and the average new-build house misses thermal efficiency standards by between 200% and 300%. As a result, the fuel bills and the CO2 emissions associated with them are, on average, 2.6 times greater than expected. Mind the Gap The sad fact is that there’s a significant gap between the designed thermal performance of a house and its built performance. Ventilation and high-performing components such as windows and doors are specified and need to be correctly installed. Construction mistakes such as cold bridges and sub-standard materials all contribute to the shortfall. This thermal performance gap is a major problem. Today, it may surprise you that a £250 washing machine might have a more rigorous end-of-line test than a £250,000 house! A new building’s Heat Transfer Coefficient (HTC) – the standardised measure of insulation performance – is not determined directly but calculated on paper using a government-approved methodology (Standard Assessment Procedure – or SAP). There is no mandated verification test to compare the specified HTC to real-world performance. Measuring the real-world thermal efficiency of a building is a time-consuming and expensive undertaking and is not routinely carried out. The gold standard method of measuring a building’s HTC is a co-heating test - the building is heated until it reaches a steady-state where, put simply, the energy input equals the energy output. This test typically requires between two to three weeks and, as a result, would not be appropriate for routine commercial applications at building sign-off. Making measurement manageable Veritherm identified an opportunity to offer an accessible service to measure the real-world thermal performance quickly and with minimal disruption. The company’s idea was a complete departure from the co-heating method; they surmised that it could be possible to accurately infer the thermal performance by measuring the rate at which the building cools overnight.

Nathan Wrench

Veritherm worked with Cambridge Consultants to validate this theory. This included developing theoretical mathematical models and building a test house on which to test the models in a realistic environment. Having established the validity of the approach, the next phase was to design a complete system solution that included networked sensors, a cloud-based backend and an intuitive user interface. The system measures the internal and external temperatures of the building over a heating period, typically of four to five hours, and the same measurements continue over a cooling period of at least the same length. During both the heating and cooling phases the power consumption of the building is also measured. The entire test is carried out over a single night to avoid the necessity of estimating insolation. The next stage was to deploy the complete system in an actual building and confirm the measurements taken by the Veritherm system matched the performance of the building as measured by a coheating test. The outcome of these tests showed that, in all observed cases, Veritherm results differed only slightly to a good co-heating test, indicating that the platform is a valid method for verifying the thermal performance of UK houses. This test offers a practical method for screening thermal performance at the sign-off of building work. It can verify that the materials specified by the building’s designer have been installed appropriately and that the overall thermal performance of the building is in line with its design specifications. Critically important, the test is performed in a single overnight automated process by a trained operator without specialised knowledge or in-depth technical expertise in the processing or interpretation of the data. Bringing this novel service to market has created a new business for Veritherm. The solution offers an accessible tool to identify poor construction practices and thus help to reduce the gap between design performance and built performance. Armed with this knowledge, the building industry has the opportunity to positively impact the energy consumption of new built domestic housing. Looking at this in the broader context of achieving the UK’s net-zero obligations, carving a chunk out of that 18% of the UK’s CO2 emissions is there for the taking. Ultimately, will it take pressure from both government and consumers to shake up the building industry? Missing a performance target by 200% to 300% in any other product would be seen as a scandalous failure. Verifying and, in fact, certifying the thermal performance of a building, has the potential to bring about improved construction practices, reduce energy bills for occupiers and reduce CO2 emissions helping the UK achieve its net-zero obligations – what’s not to like?