Following on from my previous post on energy efficiency, I was very interested to read about a recent study by the University of Bath which shows a significant gap between the forecast energy efficiency of new buildings and their actual performance once in use.

“A correlation analysis indicated little correlation between which variables were thought to be important by the modellers [of building efficiency] and which proved to be objectively important. k-means cluster analysis identified subgroups of modellers and showed that 25% of the people tested were making judgements that appeared worse than a person responding at random.”

Various studies in recent years have demonstrated that the realised energy efficiency of new buildings is significantly below the levels forecast prior to construction, often by as much as a factor of two, a phenomenon known as the “performance gap”.

building energy efficiency

Previous studies have concluded that issues arise in the building design phase, with poor communication between key stakeholders about the expected building performance being suggested as a key problem, along with deviations from the initial design during the construction phase due to wrong or missing construction details, lack of simplicity or buildability in the design, poor construction sequencing and the incorporation of inefficient or oversized systems.

Other studies have shown that novel and advanced technologies can also be problematic as they may underperform against the manufacturers’ expectations and see performance degradations over time.

In this new paper, David Coley, Professor of Low Carbon Design at the University of Bath has identified efficiency modelling as a key issue, particularly the lack of rigour in incorporating realised performance into the modelling process:

“It’s a serious scandal. It affects all new buildings as well as the refurbishment of older ones. When one school in Plymouth was rebuilt, the energy bills for a month ended up costing the same as for an entire year in the old 1950s building. The problem is nobody checks that the building is performing as promised. There is very little regulation. They can’t be sued. It’s like a surgeon not being bothered about whether their patient lived or died,”
– David Coley, Professor of Low Carbon Design, University of Bath

The Bath study involves interviews with 108 building modelling professionals about 21 common design energy-related aspects of a building. The survey was based on a real building in which detailed energy, occupancy and temperature data had been recorded, and provided a comparison with the answers of those surveyed.

The researchers uncovered poor agreement among the professionals on which factors were important and which were not, with the level of qualification or experience of the individuals having no bearing on the accuracy of their responses. There was also a poor correlation between the views of the professionals and the control data.

building energy efficiency

Although building modelling professionals responsible for forecasting a proposed building’s energy efficiency are required to demonstrate a minimum level of competence, this largely focuses on the calculations and adherence to the legislative framework – there is no obligation to check if the predictions match realised performance post construction.

This is surprising, since producers of white goods are legally required to validate the efficiency of their products with actual performance tests, and while there may be shortcomings in the testing processes, there is at least the intention that the ratings be backed by actual performance data, which is not the case for whole buildings.

This study makes sobering reading for anyone that believes improved building energy efficiency is essential component of a more sustainable energy market. The idea that energy efficiency claims are not audited in any way is leading to waste both in building construction and operation, and placing in-necessary costs on well-intentioned clients. This lack of rigour is worrying, and unfortunately repeated too often across the sector as a whole.

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