Development and Validation of a Computer Model for Energy-Efficient Shaded Fenestration Design

Abstract

The goal of this study is to develop and validate a computerized model for an energy­ efficient fenestration system that can easily be incorporated into the architectural design process. This model is for the thermal analysis of a shaded fenestration system and considers selected effects of the solar shades. Several simulation programs have been developed for the thermal analysis of a shaded window system. However, none of the previous programs has incorporated a validated simulation model into a visually effective display such as a sunpath diagram.

The proposed methodology concentrates on the development of various new graphical aids tor effectively displaying a shaded design and develops a thermal model for calculating the heat transfer through an unshaded window at any orientation. A computerized simulation model, called the Shaded Fenestration Design (SFD) model, was developed that is capable of calculating the amount of solar radiation for a clear day as well as calculating the heat transfer through window glazing. The SFD model also provides new computerized displays of the sunpath diagrams that include the equidistant, orthographic, stereographic, gnomonic, and cylindrical projections, as well as the accompanying shading mask protractors.

The program simulates clear sky solar radiation for locations in the U.S. using the methods developed by the ASHRAE Handbook, Duffie and Beckman, and Kreider and Rabl. An anisotrophic sky model was applied for the calculation of solar radiation on a tilted surface and the transmitted solar radiation through the single-glazed window. A highly insulated experimental test box was constructed to measure the total heat gain through the window glazing as well as the amount of solar radiation on the vertical surface. A finite difference model was then developed to provide a comparative validation. The results from the proposed solar simulation model were also compared against the simulated results from the DOE-2 program.

The portions of the work that represent new contributions include: l) computerization of the four projection methods (i.e.• orthographic. stereographic. gnomonic. and cylindrical projections) for the sunpath diagram and the shading mask protractor, 2) display of the hourly intensity of solar data onto the path of the sun for horizontal and vertical orientations at varying off-south azimuths, 3) use of a moveable viewpoint for the sunpath diagram, and 4) development of experimental test sets of the measured heat gain for various shading configurations.