Energy Saving Effects of Sidelighting Strategy

Abstract

In a daylighted space, windows 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 use of shading devices is necessary to prevent overheating and provide a glare-free visual environment. The common shading devices that have been in use in buildings are exterior overhangs, interior blinds and roller shades. This study examines the impacts of an exterior louvered overhang, translucent roller shade, and blinds on the total yearly energy loads for a prototypical classroom space situated in Boulder, Colorado. Coordinated modeling, with an advanced daylight and electric lighting simulation program and a building thermal simulation program based on hourly weather data, was used to compute total yearly building energy use. Annual lighting, cooling and heating loads for a side-lit space using these shading devices were compared with those of a base case with no shading device. It was found that the total energy performance of the roller shade with a total transmittance of 10.4% was similar to blinds tilted 45o with 60% reflectance. The roller shade consumed 12.5% more total building energy than exterior 1.2m overhang.