Atrium and skylight shapes are important architectural design elements. Atrium and skylight shapes influence daylight availability within the space and, therefore, lighting energy consumption. There is a lack of prediction models for skylight transmittance and daylight availability in atriums. A new concept was developed to predict the diffuse transmittance of skylights. A skylight shape is converted into a representative shape through a shape parameter. Generic formulae for the skylight diffuse transmittance were developed under different sky conditions. A zonal model combined with the flux transfer method was developed to predict daylight availability in top-lit atriums through the prediction of the average Daylight Factor at the atrium floor and ceiling (non-glazed portion of the roof), and the local DF normal to walls. The developed DF model was compared with currently available models derived from theory and experiments under artificial skies. The results showed that the computed diffuse transmittance for translucent skylights under real pertly-cloudy or clear skies may reach up to 33% in summer and 56% in winter higher than that under CIE overcast skies. The developed zonal model yielded very close results to the models based on the finite-element method. However, models based on physical scale measurements lack general consensus among themselves, and may produce average DF values at floor level up to 45% higher than those produced by the zonal model. Physical scale models may also yield local DF values normal to walls up to 50% lower than those predicted by the zonal model.
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