Comparison of quantitative IRT to estimate U-value using different approximations of ECHTC in multi-leaf walls

Abstract

One of the properties which defines the energy performance of buildings is the thermal transmittance of their envelope. The quantitative analysis through infrared thermography (IRT) is among those methods to determine it. In addition, this method can be applied from both the interior and the exterior. In this study, the existing external IRT methods are analysed, and the comparative analysis is complemented by using new formulations of different expressions of the external convective heat transfer coefficient (ECHTC) due to correlations of both wind speeds and dimensionless numbers. Results determined that there are differences in results of thermal transmittance according to the approach of formulation used, thus affecting both types of correlations analysed. Those expressions with a larger number of valid results used the approach of convection for correlations depending on the wind speed of Watmuff et al., Liu and Harris, Lunde, and of ISO 6946, whereas for ECHTCs due to dimensionless numbers, there were limitations to obtain representative results. Likewise, clustering ECHTCs allowed to reject restrictions based on the type of surface finish and the wind direction. Finally, there were differences in the thermal transmittance value depending on the type of wind speed used.