UK researchers have sparked debate on the cause of the gap between predicted and actual building performance, controversially pointing the finger at the people who model energy performance and labelling them “modelling illiterate”.
The accusation was levelled at building energy modelling professionals by University of Bath professor of low carbon design David Coley and colleagues earlier this month in peer-reviewed journal Building Services Engineering Research and Technology.
The story has caused consternation in the UK, following the research being picked up by The Telegraph, with at least one building modelling company complaining they had been made a scapegoat for what was a far more complex problem.
In the article Professor Coley described the study findings as a “serious scandal”, likening it to the VW emissions scam.
In the UK, both residential and non-domestic buildings are required to have an Energy Performance Certificate that estimates a building’s energy efficiency on a scale from A to G. Building energy modellers use a range of computer simulation programs to calculate performance, but have no legal obligation to ensure a building’s certificate corresponds to actual performance.
The system is like the Australian NatHERS system that rates the energy efficiency of a home based on its design, and which also suffers from a well-documented performance gap. A 2014 pitt&sherry report put this down to a number of causes, including dodgy builders, energy assessors and building surveyors, as well as a lack of proper oversight.
Energy use twice what is predicted
There are claims that measured energy consumption in non-residential buildings in the UK can often be more than two times what has been predicted at the design stage, which Professor Coley said had severe financial and amenity implications for building owners, and environmental implications for governments’ Paris targets.
He said previous research had assumed these differences could be attributed to the construction and operation stages.
“However, we have revealed a new cause for the ‘performance gap’, that being the modelling illiteracy of building modelling professionals arising from the modellers being separated from the rest of the construction process and the final building,” Professor Coley said.
The researchers surveyed 108 building modelling professionals on 21 design energy-related aspects of a building, including insulation, heating, glazing ratios, airtightness and ventilation rates.
The questions were based on an actual building – a typical UK semi-detached house that had been upgraded – in which detailed energy, occupancy and temperature data had been recorded pre and post refurbishment.
“Such a building, rather than for example a large office block, was chosen deliberately to reduce the complexity of the situation and hence improve the accuracy of the human judgements,” the study report said.
However, the respondents could not agree on which elements were the most and least important in terms of their effect on energy performance. Neither amount of modeller experience nor level of qualification had any effect on accuracy. In fact, a quarter of respondents were deemed to be no better than if a member of the public were selected at random to do the work.
“A quarter of respondents were deemed to be no better than if a member of public were selected at random to do the work.”
Co-researcher Dr Ian Walker said given the findings that education or experience had no effect on predicted performance, governments needed to implement educational and policy change.
“Currently, an in-depth qualification for building modelling does not exist, meaning there is little formal training process for those entering the profession,” Dr Walker said.
“If this aspect can be addressed, part of the ‘performance gap’ could rapidly be reduced.”
Industry says story much more complex
3D performance analysis software company IES said while more needed to be done to address the gap, energy modelling professionals had been unfairly targeted.
“Yes, the ‘performance gap’ is well documented and known about in the industry,” IES communications manager Edwina Cramp said in a blog post.
“But to address it requires action by all those involved in a building’s lifecycle, from design to operation. That includes architects, engineers, energy modellers, contractors and facilities managers to name a few. The finger should not just be pointed only at building modelling professionals.”
UK Green Building Council director of policy and campaigns John Alker said the majority of buildings were not performing as expected, and agreed it was due to “a variety of complex reasons, and needs action by all those involved in the property lifecycle – such as architects, engineers, contractors and facilities managers – not just building modelling professionals”.
Ms Cramp said there were a number of industry initiatives working to reduce the gap and the “digital revolution” of the construction industry through Building Information Modelling (BIM) meant that “the industry has a vehicle to capture relevant information during design for use during the operational phase of the building as well as accountability for operational performance”.