Day lighting as a factor in optimizing the energy performance of buildings

Abstract Theoretical evidence is presented on the possibility that proper window sizing as well as proper selection of external surface to volume ratio can result in total energy savings for heating, cooling and lighting in the periphery zones of buildings. The savings are of the order of 50% relative to the windowless configuration. The optimum window are ranges from 10% to 40% of the wall area depending on the size and geometry of the spaces. The calculations were carried out for Austin, Texas using hourly weather data averaged over a 9 year period. The results of the calculations are strongly dependent on the sky illumination calculations. A model of the sky illumination that calculates the perceived intensity of illumination as a function of weather conditions and the orientation of the receptor relative to the sun is developed and the results of an empirical test run on the model are included.