Simulation and the building performance gap

This special collection examines simulation and the building performance gap. It focuses on quality assurance measures, case studies, user studies that address the development of trust in the performance calculations of designers. Papers were sought that ‘describe the challenges, innovative methodologies, or strategies to enhance reliability and effectiveness’. Most papers in this special collection focused on the gap between calculated building energy performance and measured performance. People who produce simulation results need to explain to the users of the results why this gap exists. The gap arises from the misconception that a (simulation) model of reality can predict the future. A myriad of papers have highlighted the potential causes of the gap. The likelihood of the gap remaining is high, even after removal of the obvious causes such as training those making the calculations, and using realistic input values for material properties and equipment efficiencies. The tendency of critics of building performance simulation is to suggest abandoning their use while pointing to the aphorism attributed to the statistician George Box which states ‘All models are wrong’. These critics seem to ignore the value of models in helping ensure that time and money are not being invested on issues with little benefit to building occupants or investors. Box stated this benefit memorably as ‘It is inappropriate to be concerned about mice when there are tigers abroad’. Building performance simulation has the potential to provide very detailed information that could allow code officials to quantity the risk that buildings might perform in a different manner than has been modelled. In order to achieve this goal, simulation experts need to be far more engaged with definition of and compliance with building energy performance.