Insights from in-situ measurement of building fabric thermal performance of three zero energy dwellings in UK

Abstract

In-situ testing of actual building performance is vital to achieve the UN Sustainable Development Goal 11 (Sustainable cities and communities) in reality, given the growing concern that low energy dwellings often underperform against design specifications. This paper presents the methodology and results of in-situ measurements of the building fabric thermal performance of three zero energy dwellings in the UK, using blower door test (air permeability), heat flux measurement (thermal transmittance/U-value) and thermal imaging survey (heat losses). Despite being designed to high thermal standards, air permeability tests showed that none of dwellings met the design air permeability target, with actual results of 5.4 - 7.5 m3/h/m2@50Pa. Air permeability was found to have increased after the initial test due to post-completion alteration to the fabric, although it remained within the UK Building Regulations requirements. Heat flux measurements showed poor thermal quality of the walls and roof section even for the 'good' sections that were measured. Thermal imaging surveys revealed where fabric performance was being compromised. Air leakage pathways were found around door/window openings, penetrations and junctions between walls and ceilings indicating poor workmanship. Insights from this study have reinforced the need to have updated as-built energy models with in-situ performance data to reduce performance gap.