The energy demand for electric lighting as a consequence of different architectural building features and lighting plant characteristics

This paper focuses on energy demand for electric lighting in office buildings: in particular, aim of the study is to estimate the variation of electric lighting energy demand in response to changes in some building features such as orientation, room depth (from a private to an open-plan office), window size (expressed in terms of window- to-wall ratio, which was varied in the range 0,2 – 0,6) and external obstruction (varied in the range 0° - 75° of obstruction angle). Furthermore, the impact of a daylight responsive lighting control system with respect to manual control is also considered. As a first step, the analysis is carried out for the climatic conditions of Turin, Italy (latitude: 45° north). The software DAYSIM, which allows calculating daylighting availability and its integration with electric lighting through a dynamic climate-based annual simulation, was used for the purpose. Daylighting and energy demand were first calculated for a single office room; simulations were repeated changing the different building features. During a second phase, a number of simplified sample office buildings were considered: these were obtained by putting together some of the north-facing and south- facing single rooms which were simulated individually. The Lighting Energy Numerical Indicator value (LENI) was finally calculated for the sample buildings. The results obtained in the study are intended to provide architects and designers with more detailed information about the consequences on daylighting and energy demand for electric lighting due to different architectural solutions, as well as, the other way around, with strategies to guarantee a desired energy and/or environmental performance. Results are hence expressed in terms of: comparison between the lighting energy demand for a manual and for a daylight-responsive control system; correlation of the energy demand to a daylight factor criterion; percent variation of energy demand as building features vary (room depth, WWR, obstruction angles), highlighting for which combination a manual or a daylight responsive control system is worthwhile.