Evaluation of Radiance’s GenBSDF capability to assess solar bidirectional properties of complex fenestration systems

Abstract

Worldwide, buildings sector consumes more than one fifth of total energy (EIA 2013). This value can significantly vary among countries. For instance, the building sector accounts for around 40% of energy consumption in both the UK (DECC 2013) and the
US (DOE 2013), while it is responsible only for 28.8% in the case of Chile (MinEnergia). The three largest uses of energy in buildings are lighting, heating and cooling. Moreover, people spend over 80% of time inside buildings, which should provide a healthy and comfortable indoor environment. Properly designed window systems can cause significant energy savings through reduction of solar gains, which
may also improve occupant’s visual and thermal comfort (Bessoudo et al. 2010; Wienold et al. 2011; Tzempelikos et al. 2010; Tzempelikos and Athienitis 2007).
The most effective method for reducing solar heat gains on window systems is to block the solar radiation on the external side of them, which could be done by installing shading devices. These devices can be classified in two groups. The first group corresponds to
overhangs, vertical and horizontal fins and awnings, whereas the second group corresponds to Complex Fenestration Systems (CFS) which include fenestration attachments that can show complex thermal and optical behaviour (ASHRAE 2103).
CFS may be composed by non-specular elements. Some examples of CFS are venetian blinds, vertical louvers, screens and roller shades. For instance, Figures 1a and 1b show a shading system and a CFS, respectively.