Solar-assisted naturally ventilated double skin façade for buildings: Room impacts and indoor air quality

Although the performance of naturally ventilation double-skin facade (NVDSF) assisted by solar radiation has been widely demonstrated for building energy saving, there are still several unsolved issues towards its application regarding the user space's side and its air quality. This study focuses on two aspects through validated CFD simulations: firstly, a theoretical model is calibrated for the use of an NVDSF connected to a room, with its validity examined by different solar intensities and applicable scenarios clarified; secondly, the age of air and ventilation efficiency under each scenario are evaluated. Results reveal the impacts due to air supply vent sizes, installation heights and aspect ratios, identify discounts in ventilation rates up to 14.8%, 15.3% and 2.9%, respectively. With a fixed air supply vent, different NVDSFs locations deliver almost identical natural ventilation rates (no more than 1.7% differences between cases), but significantly different indoor air quality – the difference in ventilation efficiencies can be up to 18%. An NVDSF located furthest to the air supply vent delivers the best indoor airflow distribution, with more fresh air coverage across the room and reduced bad circulation. The solar irradiation's (I) impact on natural ventilation rate (V) has been identified as V=0.004I0.33 (new theoretical model) and V=0.002I0.42 (CFD), which shows a good agreement with an average discrepancy of 6% for solar intensities 100–1000W/m2. This study highlights the importance of evaluating indoor air quality in addition to the ventilation rates for an NVDSF with a room, and provides a more accurate theoretical model for transition seasons' ventilation that can reflect impacts from solar intensities to assist in future strategy-making for mixed-mode operations in buildings.