Using In-Situ Building Fabric Thermal Performance Testing to Calibrate As-Built Models of Low Energy Dwellings in the UK

This paper presents the methodology and results of in-situ building fabric thermal testing to calibrate as-built energy models of three low energy dwellings in the UK, so as to examine the gap between the as-designed and as-built energy performance. The in-situ tests included air permeability testing, along with thermal imaging and heat flux measurement. Despite the dwellings being designed to high thermal standards, heat flux measurements showed poor thermal quality of the walls and roof section even for the ‘good’ quality sections that were measured. Thermal imaging surveys revealed air leakage pathways around door/window openings, penetrations and junctions between walls and ceilings indicating poor detailing and workmanship. Air permeability (AP) was found to have increased after the initial test due to post-completion alteration to the building fabric. Though the results were higher than expected they were within the UK Building Regulations limiting fabric parameters. Calibration of the model through temperature monitoring provided less extreme projected energy performance gap than simply replacing the designed AP values and U-values with test results. Insights from the study have reinforced the need for national Building Regulations to require as-built energy models with in-situ test data to measure the gap between intent and outcomes.