| Abstract | The topic of this paper is part of a project to develop software to analyze the optical characteristics anddaylighting performance of conventional and tubular skylights. Skylights are found in many building types,such as commercial and institutional buildings, houses, shopping malls, hotels, etc. However, skylightmanufacturers lack design tools to predict the optical performance of skylight products. Prediction ofskylight optical characteristics is a difficult task, due to the complexity of skylight shapes that change withdesign requirements. This paper presents an analytical model to compute the overall optical characteristicsof barrel vault skylights under direct beam light. The model is based on a ray-tracing technique, and canhandle skylights with different glazing types (gables opaque, or glazed with different glazing types from thetop surface of the skylight), different shapes (short/long with high/low-rise profiles) and different orientation(north-south, west-east, or any direction). Applications of the model showed that barrel vault skylightstransmit much more light at high incidence angle on a horizontal surface than similar flat skylights. Theskylight length-to-radius ratio (L/R) has a significant impact on the optical characteristics. Short skylights(L/R = 2) with uniform glazing transmit approximately the same amount of light at any sun position.However, long skylights (L/R = 5) transmit about 64% more light when the sun is perpendicular to theskylight axis than when the sun is parallel to the skylight axis. Short skylights with clear gables and tintedtop transmit substantially more light than flat skylights with similar tinted glazing, particularly when the sunis parallel to the skylight axis. |
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