Novel in situ measurement methods of the total heat transfer coefficient on building walls

Abstract The performance gap between the design and the as-built energy performance of buildings is considered a significant risk that may compromise the efforts on meeting the carbon reduction targets set by governments in Europe. The relative importance of irregularities or defects within building walls is more prominent when the thermal insulation level increases. It is thus necessary to quantify the global thermal insulation level of building walls (i.e., including thermal bridges). Classical contact measurement methods only allow local measurements and would thus require the use of a high number of sensors which would limit their applicability. Besides, the presence of thermal bridges prevents the use of contact heat flux measurements because of the 2D or 3D nature of the associated heat transfers through the building walls. To overcome these limitations, the present study proposes an alternative approach consisting in measuring the heat flux on one location and extrapolating its value on the whole building wall through the measurement of the total heat transfer coefficient. Therefore, we developed and/or further improved five different in situ measurement methods of the total heat transfer coefficient on building walls. The measurement methods were thoroughly tested indoor thanks to lab-scale experiments carried out both in steady-state and transient regimes. The results obtained demonstrated the accuracy and the robustness of the proposed methods, as well as their intrinsic limitations. These in situmethods can be used to assess the heat losses on a whole building wall, including the contribution of thermal bridges.