Effects of daylighting options on the energy performance of two existing passive commercial buildings

Results are presented from a study of south facing roof apertures on two buildings from the U.S. Department of Energy's Non-Residential Experimental Passive Buildings Program. This study is part of a broad effort to evaluate the energy, functional and economic performance of all twenty buildings in the program based on on-site observations and physical data. The work reported here supplemented the basic building data with illumination data from physical models and from the buildings themselves, and with additional observations and measurements. Energy analyses were performed in order to examine more comprehensively the daylighting systems incorporated into the buildings, especially as they relate to (a) interaction between heating, cooling and lighting requirements; (b) integration of the electric lighting and daylighting systems and (c) functional effectiveness and occupant interaction with the daylighting system.Results of this study provide quantitative information on the energy benefits of the daylighting systems as designed and used in the two buildings examined. The daylighting strategies are shown to provide substantial energy savings over similar non-daylit buildings. In both buildings, manual control of the electric lights is used; the evaluation demonstrates that in these buildings this proves to be an extremely effective strategy. Factors contributing to this result are discussed in terms of the observed behavior of the occupants and functional requirements of the buildings.