Variazione del Fattore di Luce Diurna in funzione della morfologia urbana e della riflettanza delle superfici esterne

Indoor lighting levels and energy demand for lighting depend on urban morphology and building envelope technology. The aim of this study is the analysis of the relationship between daylight availability in indoor environments and urban morphology, and to quantify the influence of the visible reflectance of building skin on indoor lighting level. New Building codes (existing or going to be approved as the new one of Milano), use the Average Daylight Factor (ADF) as an index of daylighting performance: any of its proposed calculation methods are the simplified ones, based on the Italian standard UNI 10840. This method is effective in preliminary design phase even though the mean value excludes the contribution of the optical properties of outside surfaces. This contribution, on the other hand, could modify the lighting level and the indoor illuminance distribution for high-density urban environments. Furthermore, the reflectance of building envelope surfaces is affected by weathering and soiling. Improved daylight analyses should thus take into account the impact of ageing on the optical properties of building and urban surfaces. Herein we present the results of a numerical simulation activity, by means of ray-tracing model, showing the dependence of DF on urban morphology, and on the reflectance of exterior surfaces. Moreover, optical properties of external surfaces change with time, due to weathering and soiling. With this numerical modelling activity, the light reflectance decay of building surfaces can influence by more than 15-20% the availability of natural light into the indoor environment.