The Influence of Blinds on Temperatures and Air Flows within Ventilated Double-Skin Façades

Ventilated façades have become an increasingly employed feature in the design of low energy buildings over recent years in that they offer the attractive features of a conventional glass façade but without the thermal disadvantages. These façades consist of a double skin surface, the outer layer of which is of toughened glass, and the inner layer of which usually comprises conventional double-glazing, behind which is the occupied space. The cavity formed by the outer and inner layers is ventilated, and frequently contains a blind. This blind, together with the cavity ventilation, provides a means to control the heat transfer across the façade, in terms of solar gain transmission and recovery of heat lost from the interior. A three-year project, funded by the UK’s Engineering and Physical Sciences Research Council (EPSRC), has investigated the thermal and airflow performance of ventilated façades. A series of parametric experiments have been performed using the Large Scale Solar Simulator at Loughborough University. Results from these experiments have been used to validate models of airflow and thermal behaviour developed at De Montfort University. Advice on practical application and industrial practice has been provided by Arup Research and Development and IT Power. The result of the research is an improved understanding of the thermal and air flow behaviour of such ventilated double skin façades. The effects of external conditions, solar irradiation and exterior air temperature, on double skin façades with differing internal characteristics are presented and analysed in this paper. In particular, the effect of the blind blade angle on cavity temperatures and ventilation air flows will be reported, together with an outline of the guidance that is now emerging to assist designers of such façades. INTRODUCTION Detailed measurements of the thermal performance of building elements are essential in the validation of models used for performance prediction. A collaborative project funded by the UK’s Engineering & Physical Sciences Research Council (EPSRC) has recently been completed. The focus of this project was a detailed investigation of the performance of double skin façades, Proceedings of Clima 2007 WellBeing Indoors