Prediction of energy demand for lighting in buildings with different architectural features

This paper presents a mathematical model linking the energy demand for lighting for a room, expressed in [kWh/m2year], to a number of architectural features influencing the indoor daylight availability, and to two control systems for lighting fittings: a manual on/off switching system and a daylight responsive system which dims electric lights depending on the internal illuminance due to daylight detected on the working plane. The architectural features that were varied in the study are: site, orientation, window size and glazing visible transmittance properties, room size and presence of obstructing buildings. The lighting energy demand of the room was calculated as a function of the daylight availability and the type of controls system, considering office rooms, with typical lay-outs, working time and illuminance requirement. The mathematical model to estimate the lighting energy demand as a function of the previously cited variables was built upon the data obtained from a parametric study carried out through the simulation, with Daysim, of a large amount of office rooms. The mathematical model is intended to be used since the earliest design stages to help the design team address the first choices concerned with the building mass, shape, orientation, glazing and shading systems and to predict the associated energy demand for lighting.