Numerical sensitivity analysis of the energy performance of building envelope with dynamic conditions

The accurate energy performance assessment of building elements remains an active research topic. Studies have indicated that the thermal mass of building envelopes could influence heat losses in dynamic conditions and lead to significant difference in performance compared to steady-state conditions. This article aims to identify the relevance of using dynamic simulations instead of steady-state calculations for the energy performance assessment of building elements in Denmark. A numerical sensitivity analysis is performed on various parameters. The Monte-Carlo approach is used to perform numerous BSim simulations, which are then compared to standard steady-state calculations. The varied parameters include solar absorptance, ventilation in cavities, insulation material, insulation thickness, and orientation. Preliminary results indicate that dynamic conditions can significantly alter the wall heat losses, by up to 20% when compared to steady-state conditions. However, when aggregated, the differences average out to only 4% lower heat losses. When focusing on the thermal inertia of insulation materials, denser insulation materials only slightly delay the heat loss in the building element, but this effect is nullified over longer periods. The sensitivity analysis indicates that the most influential parameter is the solar absorptance, while the type of material is close in significance to the other parameters. The specific heat capacities and density of the insulation layer does not have a significant influence compared to its thermal conductivity. Thus, insulation materials with higher thermal mass do not seem to significantly improve the thermal performance of a building envelope.