Solar radiation on naturally ventilated double skin facade in real climates: The impact of solar incidence angle

Although the angular dependence of optical properties has long been recognised in transparent glazing facades, the impact of such dependence on natural ventilation between glazing has not been widely studied, especially in building facades with high solar incident angles. To better cope with such properties with the prevailing implementation of transparent building envelopes, this study investigated the effects of high solar incidence angles for vertical building facades through theoretical and numerical methods. The theoretical model validates the features of the optical properties simulated by the numerical model, supporting the numerical model's capability of revealing the radiation reflection, absorption, and transmission when multi-reflection is present. Then, such angular impact is studied with typical seasonal data in three cities, namely Shanghai, Melbourne and Chicago. Results firstly revealed the discrepancies between considering or ignoring multi-reflection between two glazing facades at varying incidence angles. Due to the opposite variation trend in reflectivity and transmissivity over angles, there is a critical solar incidence angle at 75° when multi-reflection's impact on natural ventilation reaches its highest. After that, the influence is reduced to its minimum. Identifying this angle helped highlight the enhanced natural flow due to realistic angular-dependent reflections between transparent panes, namely, under-estimation occurs if the angular dependence is not considered in the setting of optical properties. The analysis in three cities also revealed the climatic and locational impact of the angular impacts on ventilation rates. By addressing the impact on the optical and thermal performance of transparent facades, the dynamic variation of solar conditions can be more accurately integrated into passive building designs.