The use of natural daylight to reduce electric fighting loads and space conditioning equipment operation in an office building is investigated. Energy requirements from thermal simulations of a non-daylit and a day/it building are studied using the DOE2.1B program. The economic impact of varying glass-to-waft-area ratios (GWAR) on daylit building is also analyzed. The effects of climatic conditions are investigated by simulating therma/ perfor. mance at four representative North American cities. Four utility rate structures are used in the economic analysis to provide a range of typical energy costs.

Energy simulation results for a day/it building predict up to a 17% decrease in electrical energy consumption as compared with an identical non-daylit building. An economically viable daylit building is influenced by the available daylight illuminance, the utility rate structure, and the design window area.