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Designing the Window to Fit a Shading Device, a Reversed Method for Optimizing Energy Efficient Fenestration

By A. Sherif and E. Abbas


Solar radiation passing through a window contributes significantly to cooling loads and energy consumption, especially in hot climates. Most CAAD tools handling energy efficient design help designers to define the optimal shading device to protect a window of a certain shape, usually a rectangle, but some parts of the rectangular window (such as lower corners) are typically difficult to protect. Usually the whole shading device becomes bigger to shade these corners, which over-shades the rest of the window, increasing artificial lighting and heating loads.  It also increases the complexity, visual impact and cost of the shading device.  Changing the shape of the window by cutting these corners may reduce the size of the shading device considerably, which opens way to a different or even a reversed- approach: “Designing the window to fit a shading device instead of designing the shading device to fit the window!” This approach has several potential applications. The building form itself sometimes works implicitly as a shading device. For example, if the building plan shape is a U or L shape, some parts of the walls become shaded, the windows can be placed in these shaded parts, and the window shape can be designed to fit the shadow pattern caused by the building form, changes in the building profile gives similar chances to design windows that fit the shadow pattern. Conceptually, this approach makes energy efficiency a form giving attribute, helping to create innovative facades, while giving an energy efficient configuration for both window and its shading device. CAAD tools can help the designer adopt such an innovative approach, by proposing the window shape that suits an arbitrary shading device created by the designer or a building mass. This paper examines the validity of the approach and introduces the approach required for developing a software module that can be integrated with other CAAD tools such as the Ecotect software.  This would enable the designers to use this approach. The method handles the complexity of time-dependent solar geometry and radiation intensity, the geometry of both the window and shading device, and the designers set of objectives, enabling the designer to define the required configuration of window and shading device

Topics: Algorithm, Energy Efficiency, Low-Energy Architecture, Oprimization, Shading Devices, Windows
Year: 2011
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