Optimal daylight factor for energy-efficient toplighting system

Skylights can introduce considerable heat gain and loss that may offset the benefits of electric light savings and cause an increase in yearly net energy use. The design of a toplight system needs to take into consideration different toplighting types, including aperture size and orientation, electric lighting control, and, most importantly, the local climate. This study examines the impacts of aperture size (day light factor) for four combinations of toplighting strategies and glazing types on the total yearly energy loads for a prototypical open office space situated in four different climates. This study shows that toplighting systems designed to meet a 2% daylight factor are not optimal. The optimum daylight factor varies depending on toplighting type, local climate, and the thermal and solar heat gain properties of the glazing.