Indoor daylight climate-comparison between light shelves and overhang performances in Madrid for hours with unit sunshine fraction and realistic values of model reflectance

In the present paper we have compared the daylighting performance at a poin t placed at 50 cm from a south-facing opening in 1:10 models painted for re alistic reflectance values, of two light shelves and an overhang, using mea surements performed during 1 year. The light shelves and the overhang produ ced the same shading effect, as both were designed for a vertical shade ang le of similar to 50 degrees, adequate for south facing shading devices duri ng the overheated period in Madrid (Spain). The comparison is performed fro m 06:00 to 12:00 h (true solar time), using data obtained when the hourly s unshine fraction is 1. The study of the measured illuminance provides a qua ntitative assessment of the advantage of using a light shelf instead of an overhang, both giving the same solar protection. A detailed study of the di fference between correspondent illuminance values in the models equipped wi th metacrilate and mirror light shelves and the model equipped with the ove rhang has been performed. The difference between the daylighting performanc e in the model equipped with the metacrilate light shelf and the model with the mirror light shelf at the mentioned measurement point is also studied, and the period of the year when each of the light shelves performs better than the other is determined. The performance of the two light shelves is r elated to important differences between their mean reflectance for the spec ular component and after excluding the specular component, as measured with a spectrophotometer for a 4 degrees incidence angle. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.