Summary

Windows can introduce considerable heat gains and losses 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 overhang and interior blinds and roller shades. This study examines the impacts of exterior overhang, roller shade, and blinds devices on the total yearly energy loads for a prototypical classroom space situated in Boulder, Colorado. The measured bi-directional transmittance characteristics for a roller shade were applied to the yearly daylight availability analysis. 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 yearly total building energy use. Annual lighting, cooling and heating loads for a side-lit space using the shading devices were compared with those of a base case with no shading device. Of special interest was the performance of the new roller shades in comparison to blinds and exterior overhang as they are installed in the new New York Times building. It was found that the total energy performance of the roller shade with a total transmittance of 10.4 % was similar to blinds tilted 45 ˚ with 60 % reflectance. The roller shade consumed 12.5 % more total building energy than exterior 1.2 m (4-ft) overhang