Validation of a coupled pressure-equalization-thermal-mechanical model to study double-skin facades

¹ Ghent University, Faculty of Engineering and Architecture, Sint Pietersnieuwstraat 41 B4, 9000 Ghent, Belgium
² Permasteelisa Group, Group Innovation and Technology, viale Mattei 21/23, 31029 Vittorio Veneto, Italy

^* Corresponding author: Nathan.VanDenBossche@ugent.be

Abstract

Although double skin façades are a well-known façade system, still few experimental data and numerical approaches exist in literature that couple their thermal behaviour and pressure equalisation with the structural response. The reason is that, differently from insulating glazing units, the extent of the problem is trivial when designing ventilated double skins. Indeed, the leakage of the double skin cavity is large enough to avoid any response of the internal cavity pressure to its temperature variations. However, during the last years Closed Cavity Façades, a new trend of double skins, have been applied in order to achieve high performances in terms of thermal and acoustic insulation and providing at the same time valuable benefit with regards to maintenance cost reduction. The CCF low levels of air permeability are responsible for a strong correlation of pressure and temperature of its cavity and the phenomenon needs an accurate model to support the design. Indeed, an optimal design of the outer and inner skin should consider the skin interactions and their coupling through the cavity, under the dynamic temperature and variable mass within the cavity itself. The mass variation is governed by two counteracting effects: on one side the dry and clean air that is pumped into the cavity in order to avoid the risk of condensation, on the other side the mass flows through the skin openings that connects cavity with external and internal environment. Moreover, the pressure is also affected by the interior and exterior air pressures that induce a deflection of the inner and outer skin. A numerical calculation procedure was developed, integrated with commercial codes commonly used in façade design, in order to provide a unique assessment tool for the coupled thermal-mechanical design of double skin facades. The tool has been validated by means of an extensive experimental campaign and the different relevant effects have been described.