This paper presents new evidence from a nationwide meta-study investigating the magnitude and extent of the difference between predicted and measured energy performance (energy performance gap) of over 50 low energy dwellings in the UK. Statistical testing of predicted and measured energy use is undertaken to assess the impact of occupancy related factors (number of occupants, occupancy type, pattern) on energy performance, and to predict the likelihood of the space heating energy performance gap in UK new build housing. The dataset was drawn from the UK Government’s National Building Performance Evaluation programme – which included the final reports, Standard Assessment Procedure (SAP) calculations and Domestic Energy Assessment and Reporting Methodology (DomEARM) results – and comprises 30 Passivhaus (PH) and 62 non-Passivhaus (NPH) dwellings, covering different built forms and construction systems. The majority of the sample comprised social housing dwellings built with masonry and timber frames and equipped with mechanical ventilation heat recovery systems. Although the average annual energy use (gas and electricity) in the PH and NPH dwellings was found to be 73kWh/m2 and 117 kWh/m2 respectively, electricity use was not significantly different between the two groups. All dwellings in the sample performed better than UK Building Regulations, however average energy use was higher than predicted by an average of 60%, but as much as 147% in PH and 241% in NPH dwellings. The overwhelming majority - 13 out of 14 PH and 35 out of 43 NPH dwellings - did not meet the predicted energy use, demonstrating a performance gap of 22 kWh/m2/year and 45 kWh/m2/year respectively. Occupancy was found to influence 45% of total energy use, with occupancy pattern being more critical than occupancy type and number of occupants. Despite the high levels of fabric thermal standards, space heating was found to be the largest energy end use (28% in PH and 42% in NPH dwellings) followed by domestic hot water (28%) and small appliances (21%), while the ratio of regulated to unregulated energy was found to be 70:30. The probability of an energy performance gap in space heating occurring in the population of new build housing was found to be over 80%. The study findings are important for bridging the gap between intent and actual performance of new low energy housing.
Gupta, RajatHoward, AlastairKotopouleas, Alkis
Faculty of Technology, Design and Environment\School of Architecture
Year of publication: 2019Date of RADAR deposit: 2019-05-22