Performance of lightweight and heavyweight building walls with naturally ventilated passive and active facades

Well-designed ventilated air-spaces behind external claddings in the building envelope can potentially reduce thermal energy flow in the entire wall structure. In this study, the impact of the dynamic thermo-hydraulic behavior of the flow in the naturally ventilated cavity on the performance of lightweight and heavyweight wall assemblies with traditional passive and active (i.e., BIPV) facades is investigated. A numerical transient 2-D model validated against experimental measurements is employed to perform the analysis using actual weather data and building practices in Europe, particularly in Switzerland. The results reveal that the change in the external cladding type from the passive fiber cement to the active PV façade can increase the time lag of the wall structure up to 2 h in summer and decrease it up to 1 h in winter. The maximum difference between the amplitudes of the heat flux through the interior surface for a wall assembly with the lightweight wall core is 1.5 times higher compared to a heavyweight wall core. The results show that enlarging the cavity thickness behind external claddings from 45 mm to 110 mm can increase the heat flow through the cavity up to 1.5 times. It is also shown that reflective insulation on the cavity surface adjacent to the wall core could increase the cladding surface temperature by more than 30% compared to the case without reflective insulation. This research shows that replacing the passive cladding with an active façade could affect the performance of the entire wall assembly, which highlights the importance of analyzing the active ventilated wall structures to transition towards modern building skins.