Thermal characterization of building walls under random boundary conditions

This work aims to improve the knowledge on dynamic thermophysical characterization of building envelopes by comparing three numerical methods applied on an experimental wall made of masonry brick. The thermal conductivity λ and the thermal capacity ρcp are determined by performing a data fitting optimization between the experimental measurements of the heat flux and the heat flux resulting from these numerical models. The experimental device consists of a thermal box with a controlled ambiance through a radiator linked to a thermostatic bath and placed inside the thermal box, on the opposite side facing the wall. Three different methods were examined: The Heat Transfer Matrix analytical method (HTM) using the heat transfer matrix, the Finite Element Method (FEM) using COMSOL Multiphysics® software, and the Building Simulation Model method (BSM) using TRNSYS® Type 56 coupled with Genopt® optimization tool. The reproducibility of the methods was also validated through two other datasets (one random and one harmonic). The obtained results were satisfactory for both λ and for ρcp and for the three studied methods with deviations less than 5% between the results of the different methods. The data logging duration for random boundary conditions was found to be around five days while in harmonic boundary conditions two days were sufficient for the solution to converge.