Optimum Shape of External Shade for the Window to Minimize Annual Solar Heat Gain and to Maximize View Factor
One of the most fluctuating components of space cooling load is associated vfith solar heat gain from windows. Overhangs, side fins or screen type of sun shades are widely used to avoid unwanted heat from the sun. On the other hand the window is expected to provide sunlight into the occupied space and allow people to look outside through it. Considering that the design of shading devices should be coordinated to both of these factors in conformity with aethetics, the author developed a procedure to determine the optimumshape of external shade for a rectangular windo:w of a given proportionfacing to a specified orientation so that it could intercept direct radiation as much as possible and be fabricated with a minimum araount of material, providing a maximum possible view for the occupants. Iteration process is required to obtain the geometry of the sun shade composed of two pairs of horizontal and vertical flat plates with optimum width and tilt angle. This is followed by the estimation of the annual total solar heat gain from the window with the brise-soleil thus designed, taking account of reflection and re-radiation from sunlit surfaces of sun shade as well as direct and diffuse solar radiation transmitted through the shade. The heat exchange problem around the shade assembly is approximately solved by the method similar to that to calculate the weighting factors relating heat gain to cooling load. The routines developed are intended to be incorporated with graphical display system or plotter drawing system so as to be an effective aid for the architectural design.
Key Words: Computer, optimization, brise-soleil, window, solar radiation, shadow, overhang, side fin, view factor, heat gain, design.
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