There are many reasons to control the amount of sunlight admitted into a building. In warm, sunny climates excess solar gain will result in overheating, in cold and temperate climates winter sun entering south-facing windows can contribute to passive solar heating, and in any event controlling and diffusing natural illumination will improve daylighting.
Well-designed sun control and shading devices can dramatically reduce building peak heat gain and cooling requirements and improve the natural lighting quality of building interiors. Depending on the amount and location of fenestration, reductions in annual cooling energy consumption of 5% to 15% can be expected. Sun control and shading devices also improve user visual comfort by controlling glare. Shading devices can differentiate one building facade from another, adding both interest and human scale to any facade.
The use of sun control and shading devices is an important aspect of many energy-efficient building design strategies. In particular, buildings that specifically employ passive solar heating or daylighting often depend on well-designed sun control and shading devices.
During cooling seasons, external window shading is an excellent way to prevent unwanted solar heat gain from entering a conditioned space. Shading can be provided by natural landscaping or by building elements such as awnings, overhangs, and trellises. Some shading devices can also function as reflectors, called light shelves, which bounce natural light for daylighting deep into building interiors.
The design of effective shading devices will depend on the solar orientation of a particular building facade. For example, simple fixed overhangs are very effective at shading south-facing windows in the summer when sun angles are high. However, the same horizontal device is ineffective at blocking low afternoon sun from entering west-facing windows during peak heat gain periods in the summer.
Exterior shading devices are particularly effective in conjunction with clear glass facades. However, high-performance glazings are now available that have very low shading coefficients (SC). When specified, these new glass products reduce the need for exterior shading devices.
Thus, solar control and shading can be provided by a wide range of building components including:
• Landscape features such as mature trees or hedge rows;
• Exterior elements such as overhangs or vertical fins;
• Low shading coefficient (SC) glass; and,
• Interior glare control devices such as Venetian blinds or adjustable louvers.
The following design considerations generally hold true for most buildings in most climate zones:
• Fixed overhangs on south-facing glass should be used to control direct beam solar radiation.
• To the greatest extent possible, the amount of east and west-facing glass should be limited since these are harder to control than south glass.
• When east and west-facing glass is used, landscaping may be considered as an important element to shade east and west exposures.
• Interior shading devices such as Venetian blinds or vertical louvers should not be expected to reduce cooling loads since the solar gain has already been admitted into the building.
Sun control and shading devices can make all the difference between a building that overheats in summer and is unnecessarily cool in winter, and one that is climatically appropriate, comfortable for users, limits discomfort due to glare, and conserves energy thus resulting in lower monthly recurring costs.
It follows that in order to assure success one should assign high priority to these items during the decision process attending any responsible building design.