Comparison of transient hygrothermal modelling against in situ measurement for thermal transmittance

Abstract

Thermal transmittance (U-values) of exterior walls represents a source of uncertainty when estimating the energy performance of dwellings. It has been noted in research that the standard calculation methodology for thermal transmittance should be improved. Subsequently, hygrothermal analysis has been used as an accurate building design tool due to its incorporation of climate-specific effects on construction assemblies such as moisture retention and release. In situ measurement of thermal transmittance could also be an effective tool for evaluating the material performance of assemblies of a building. This paper provides the context, research process and analysis of four case studies situated in Dublin, Ireland. The case studies offer an account of the in situ thermal transmittance of exterior walls and link these to hygrothermally simulated comparisons along with more traditional design U-values. The findings of this paper identify discrepancies between in situ and design U-values, using measurement, hygrothermal simulation and standard method U-value calculations. This study can form the basis for further research on retrofit of the Irish housing stock. Furthermore, the paper offers a source of information for researchers and designers exploring the performance of external walls to anticipate best practice detailing and in situ thermal performance values.