Classroom Daylighting Performance with Shaded Window at the Equator

Juliana Portela Vilar de Carvalho, and Aldomar Pedrini

Postgraduation department of Architecture and Urbanism, Federal University of Rio Grande do Norte (UFRN), Brazil

Abstract: This paper aims to demonstrate a method to assess the classrooms daylighting performance with shaded windows, at the Equator, in hot and humid climate, using a computer simulation program, DAYSIM. The study concerns the city of Natal, Northeast of Brazil, 5º S, on the coastal area, whose principles of passive building design emphasize large and shaded openings to promote natural ventilation and avoid solar thermal gain to achieve thermal comfort. Such strategies also contributes to daylight comfort, promoting adequate diffuse light and avoiding the excess of glare due to the direct daylight. On the contrary, unshaded fenestration may lead the users to close the curtains and turn the electric lights on. The method assesses the daylighting levels for different classroom depths, and the influence of the opening size and external shading performance. The simulated models combined three opening dimensions (20%, 40% and 50% of window-to-wall ratio — WWR), two main façade orientations (North and South), and seven types of shading (horizontal overhang, drop edge overhang, 5º sloped overhang, horizontal overhang with side protection, horizontal overhang with three louvers, double horizontal overhang, double horizontal overhang with three louvers). Analyzes based on the useful daylight illuminance (UDI) index showed limitations due to the occurrence of glare, caused by direct daylight next to the window. Detailed simulations emphasized the influence of the visible sky factor (VSF) and opening size combinations in the daylight performance. Results show that 20%WWR does not cause glare, but the daylight declination occurs significantly at 3.50 m depth. The 40%WWR causes glare in the first row of sensors next to the window, highly reduced with light shelves. Further assessments with 40%WWR and 50% WWR models reduced or eliminated the glare occurrences. The daylight zone of 40%WWR varies between 3.54 m and 4.75 m and the daylight zone of 50%WWR reaches approximately 7.20 m.

Key words: daylighting, window-to-wall ratio, shading device, DAYSIM, simulation