Simultaneously estimating functional forms for thermal conductivity and vapor resistance factor of wall insulation in situ by inverse problem

• A dual inverse method estimates effective hygrothermal properties in a wall assembly. • Datasheet and in situ conductivity and vapor resistance show significant differences. • Literature overestimates vapor resistance of EPS and conductivity of insulation. • These differences induce a bias of 9% in the annual heat and moisture flow estimates. In the design or retrofit stages, numerical simulations are a powerful tool to evaluate the hygrothermal performance of building envelopes. However, simulation results are only reliable if the building physics modeling is calibrated with accurate input data. This study reports an inverse analysis to simultaneously estimate functional forms of the thermal conductivity and the vapor resistance factor of prefabricated wall insulation layers. Inverse fully coupled hygrothermal modeling considered temperature and relative humidity measurements obtained in situ from an occupied detached house located in Quebec City, Canada. The inverse approach enabled the numerical model to better fit the in situ hygrothermal behavior of the investigated wall under actual environmental conditions. The estimated effective properties had considerable differences compared to literature data and their effect was evidenced by computing the annual heat and moisture flux. Therefore, in situ model calibration reduced inaccuracies arising from neglecting the impact of temperature and moisture content on material properties and eliminated potential differences between operating conditions and those reported by building standards.