Selection of slat separation-to-width ratio of brise-soleil shading considering energy savings, CO2 emissions and visual comfort – a case study in Qatar

Abstract

The addition of fixed external shading devices to glazed surfaces reduces the space loads and sensations of visual discomfort caused by excessive day-lighting. The slat-to-slat separation distance of the brise-soleil blinds is crucial in controlling the beam and diffuse solar radiation penetration into the space. In this study, a model of an office space with fully-glazed façade and shaded with brise-soleil was developed to quantify its corresponding daylight glare index and space load. Results were successfully validated experimentally. Then, a parametric study was carried out on the slat separation-to-width of the validated model to find the ratio that ensures no occupant discomfort caused by glare and results in maximum possible energy savings for both south and east oriented fully-glazed façade offices in Qatar.

The selection of slat separation-to-width ratio should ensure total blockage of beam solar radiation. Consequently, the sun altitude determines the ratio that yields no discomfort glare; due to the country's latitude, this ratio has to be less than unity in south orientations and slightly larger than the sine of the slat inclination angle in east orientations. The proper selection of separation-to-width ratio leads to significant energy savings which, if integrated with lighting control for internal electric lights, may reach 39.5% and 36.6% in south and east-oriented Clear glazed façade offices, respectively. For a country with high greenhouse gas emissions, this simple energy-conservation measure also provides a cheap technique that is able to reduce CO2 emissions by up to 52.7 kg/m2/year.