A Parametric Study of Window-to-Wall Ratio and Daylight Performance under Different Obstruction Conditions in High-Rise Urban Environments
DOI:
https://doi.org/10.54097/srsbhw93Keywords:
Window-to-Wall Ratio, Sky View Factor, daylight performance, daylight provision, visual comfort, high-rise buildings, parametric modelling and simulationAbstract
Daylight conditions are different across a façade in dense high-rise urban locations due to the neighbouring buildings, which limit the exposure to the sky. The study investigates the effect of window-to-wall ratio (WWR) on daylight provision and visual comfort with varied degrees of external blockage, modelled by sky view factor (SVF). Central Plaza in Hong Kong provided the case study for identifying representative obstruction conditions. SVF was calculated across the south, northwest and northeast façades, and three values 0.10, 0.30 and 0.50, were selected for investigation using a controlled reference office model. For each condition, six WWR configurations ranging from 0.10 to 0.87 were tested through climate-based daylight simulations in Rhino and Grasshopper using Ladybug and Honeybee. Performance was evaluated using spatial daylight autonomy, daylight glare probability, and spatial glare autonomy. The results show that increasing WWR generally improves daylight provision but simultaneously increases glare risk. More significantly, the metric-based daylight response is non-linear, with the biggest benefits in daylight provision often occurring at low-to-moderate WWRs, after which improvements taper down as sDA approaches saturation. Visual comfort shows a different response, with greater deterioration occurring at the lower and higher ends of the tested WWR range, while changes are relatively moderate within the intermediate range. The influence of WWR also varies with obstruction conditions: higher-SVF environments are generally more responsive to changes in WWR, resulting in increasingly pronounced differences in daylight performance as WWR increases. A similar interaction is observed for façade orientation. The south façade shows greater sensitivity to WWR in terms of visual comfort than the other orientations, whereas orientation has a comparatively limited influence on the relationship between WWR and daylight provision. The findings demonstrate the value of SVF as a quantitative descriptor of high-rise daylight obstruction and support an SVF-responsive façade strategy. Rather than prescribing a uniform WWR, façade design should respond to local obstruction conditions while balancing daylight provision and visual comfort.
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