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

Abstract

In the present paper we have compared the daylighting performance at a point placed at 50 cm from a south-facing opening in 1:10 models painted for realistic reflectance values, of two light shelves and an overhang, using measurements performed during 1 year. The light shelves and the overhang produced the same shading effect, as both were designed for a vertical shade angle of ∼50°, adequate for south facing shading devices during the overheated period in Madrid (Spain). The comparison is performed from 06:00 to 12:00 h (true solar time), using data obtained when the hourly sunshine fraction is 1. The study of the measured illuminance provides a quantitative assessment of the advantage of using a light shelf instead of an overhang, both giving the same solar protection. A detailed study of the difference between correspondent illuminance values in the models equipped with metacrilate and mirror light shelves and the model equipped with the overhang has been performed. The difference between the daylighting performance 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 related to important differences between their mean reflectance for the specular component and after excluding the specular component, as measured with a spectrophotometer for a 4° incidence angle.