Shading Devices
Have you ever pondered that there is an overwhelming contribution of light & colour in every design, painting or art work? Managing the amount and type of light, itself is a field of study. There are many different reasons why one wants or needs to control the amount of sunlight that is admitted into a building. 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 easily be achieved.
The use of sun control and shading devices is an important aspect of many energy-efficient building design strategies. In particular, buildings that employ passive solar heating or day lighting 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 day lighting deep into building interiors.
Exterior shading devices are particularly effective in conjunction with clear glass facades. 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;
Horizontal reflecting surfaces called light shelves;
Low shading coefficient (SC) glass; and,
Interior glare control devices such as Venetian blinds or adjustable louvers.
Fixed exterior shading devices such as overhangs are generally most practical for small commercial buildings. The optimal length of an overhang depends on the size of the window and the relative importance of heating and cooling in the building.
To properly design shading devices it is necessary to understand the position of the sun in the sky during the cooling season.
Shading devices can have a dramatic impact on building appearance. This impact can be for the better or for the worse. The earlier in the design process that shading devices are considered they more likely they are to be attractive and well-integrated in the overall architecture of a project.
Designing Shading Systems. Use fixed overhangs on south-facing glass to control direct beam solar radiation. Indirect (diffuse) radiation should be controlled by other measures, such as low-e glazing.
To the greatest extent possible, limit the amount of east and west glass since it is harder to shade than south glass. Consider the use of landscaping to shade east and west exposures.
Do not expect interior shading devices such as Venetian blinds or vertical louvers to reduce cooling loads since the solar gain has already been admitted into the work space. However, these interior devices do offer glare can control and contribute to visual acuity and visual comfort in the work place.
Materials and Methods of Construction. In recent years, there has been a dramatic increase in the variety of shading devices and glazing available for use in buildings. A wide range of adjustable shading products is commercially available from canvas awnings to solar screens, roll-down blinds, shutters, and vertical louvers. While they often perform well, their practicality is limited by the need for manual or mechanical manipulation. Durability and maintenance issues are also a concern.
When designing shading devices, carefully evaluate all operations and maintenance (O&M) and safety implications. In some locations, hazards such as nesting birds or earthquakes may reduce the viability of incorporating exterior shading devices in the design. The need to maintain and clean shading devices, particularly operable ones, must be factored into any life-cycle cost analysis of their use.
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