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Designing effective sun-control and shading systems

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There are various reasons why an architect should use sun-control and shading systems. These systems are growing in popularity as the construction industry focuses more on energy-efficiency and sustainability. Walls & Roofs explores the different ways to design an effective sun-control and shading system.  

The use of sun-control and shading systems is an important aspect of energy-efficient building design strategies. There are many different reasons to apply such a system to control the amount of sunlight that is admitted into a building. Buildings that employ passive solar heating or day-lighting often depend on well-designed sun-control and shading devices.

The Whole Building Design Guide (WBDG), a programme by the National Institute of Building Sciences in the United States, cites that in nearly all climates controlling and diffusing natural illumination will improve day-lighting. According to the WBDG, 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% have been reported.”

The WBDG also states that sun-control and shading devices can improve visual comfort in a building by controlling glare and reducing contrast ratios. “This often leads to increased employee satisfaction and productivity.” It also mentions that shading devices offer the opportunity of differentiating one building facade from another. “This can provide interest and human scale to an otherwise undistinguished design.”

External window shading
Applying external window shading is a great way to prevent unwanted solar heat gain from entering a conditioned space. Architects have a wide range of external window-shading systems or products to choose from to get a desired result for a specific project.

According to the WBDG, shading can be provided by natural landscaping or by utilising 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,” the WBDG states.

Luigi Zito, general manager of Hunter Douglas, explains that sun-control systems are designed and engineered for vertical, horizontal and angled applications to meet the requirements of any design. “A wide range of systems like fixed, motorized, sliding and rolling designs can be used, made from different materials. The architect has the ability to blend style and functionality, bringing a distinct look to a building’s exterior, while providing shade and comfort to occupants.”

Solar radiance and louvres
The importance of solar-protection systems are being realised increasingly by architects today as the demand to optimise internal climates through energy-efficient means intensifies.  According to Ray Jansen Van Rensburg, a representative from the sales department of Robertson Ventilation Industries (RVI), solar heat gain and solar glare are a costly and unwanted hindrance for building owners, and as such solar shading is increasingly being recommended as a preventative measure.

He says that although fixed solar shading performs well on a north-facing facade, performance is dramatically reduced on east- and west-facing facades.
“East- and west-facing facades take in a large amount of sunshine during the day, and therefore pose an often underestimated design challenge for architects when considering and selecting the correct solar-shading system.”

Jansen Van Rensburg suggests that to overcome the problems associated with fixed solar shading and to achieve optimum results, east- and west-facing facades require controllable solar shading. “Sun-tracking louvres follow the path of the sun, making sure the solar shading system is always optimised.”  Whilst controllable sun-tracking shading systems have been available to the South African market for some time, these systems typically incorporate aluminium extrusions. “The disadvantage with controllable sun-tracking shading systems that incorporate aluminium extrusions is that at some time of the day the shading system will be closed, significantly restricting or totally obscuring the occupants’ view to the outside,” he adds.

He further explains that radiation from the sun is transmitted, absorbed and reflected by the louvres. “As a result solar heat gain is prevented from passing into the building, minimising ventilation requirements and reducing cooling loads.” Reilander adds that if a controllable system is installed, adjustable louvres track the position of the sun, thereby reducing the numbers of days when the building overheats. “Equally, in winter the louvres may be adjusted in such a way that the building benefits from the heat of the sun, and they can be closed at night to reduce heat loss. At the same time, daylight levels are enhanced and levels of glare are reduced.”

Jansen Van Rensburg says that on dull or overcast days the louvres are controlled in such a way that if clouds pass over the building, the louvres will automatically open to maximise daylight entry and then later revert back to their original position.

Louvres may also be tilted for use in other directions. “They can also be arranged in a horizontal array, like a shelf, or they can be arranged in a vertical array, like a venetian blind. Such a system can be installed at an angle and the blades can take many forms, including flat blades, air-foil shapes and egg crates,” it is stated in the article. “Blades are easier to install than shelf-type shading because they have less wind resistance, and can be much lighter and easier to attach.”

These systems can be attached to the wall or they can be mounted on columns that carry their weight to the ground. “Louvres interfere with the view if they are installed in the line of sight, but they may not block the view entirely,” the article states.

Different types of external sun-control and window-shading devices
Overhangs are a simple but easy way to regulate the sun from entering a building, especially for huge and impressive window designs. Roof overhangs can make a difference as to how much one can manipulate the interior temperature with mechanical systems.

Light shelves
Light shelves are also a type of overhang mostly used inside a building. It allows daylight to penetrate deep into a building. This horizontal light-reflecting overhang is placed above eye-level and has a high-reflectance upper surface. The surface is then used to reflect daylight onto the ceiling and deeper into a space. Light shelves are typically used in buildings, as well as institutional buildings. Another option to implement sun control is to use vertical fins. Vertical fins are useful for shading facing north from summer sunlight early and late in the day.

Screens can be a first step in designing a sun-control system. These systems come in different shades and tones and can be found in any tint that the specifier wants. Exterior sun-control screens absorb and dissipate a large percentage of solar heat and glare before it reaches windows and doors. This keeps the glass and interior cool. From the outside, sun-control screening offers a uniform look to windows and doors, providing a more aesthetically pleasing overall look to home and building exteriors than a regular insect screening. Outward visibility remains good through this exterior sun-control product.

Effectiveness of interior sun-control devices
Blinds and shades can be used effectively as a tool to help prevent the intrusion of sunlight. A paper on shading strategies done by the Lawrence Berkerley National Laboratory, a research institute for the Department of Energy in the United States, cites that an interior shading system used alone has a limited ability to control solar gain. “All interior systems are less effective than an exterior system because they allow the sun’s heat to enter the building.” The paper states that the effective use of these systems also depends on user behaviour, which can’t be relied upon.

According to the shading strategy report, architects or designers should specify light colours if such an interior system will be providing the only shading in a project. “A light-coloured shading system will reflect the sun’s heat back out of a building, but may not control glare under bright summer conditions.” The paper states that this type of shading is best used as a back-up strategy. “Supply-user operated devices like motorised blinds or shades will enable occupants to adjust the shading to their individual comfort needs.”

Honeycomb shades
Cellular shades, also known as honeycomb shades, are made of a solid fabric that stacks like an accordion. If you turn the shades sideways, they look like a honeycomb beehive. The air pockets make cellular blinds very energy-efficient.  These shades are on offer in hundreds of different colours. Light-filtering cell-honeycomb shades are the most popular in terms of cell shades. Most provide total privacy while allowing light in.

Motorised blinds
Window blinds can be manually drawn using a cord or automated through motorisation.  For blinds, adding a motor can be an easy and affordable solution for multiple window openings and hard-to-reach locations. Controls for motorised blinds can be from a wall switch, keypad, remote control or personal computer, eliminating the need for cords and allowing control of otherwise inaccessible windows.

Zito says motorised systems controlled by a management system will allow users to regulate the amount of heat and light that enters a building. “It can be adjusted to daily environmental conditions.”

For most horizontal blinds such as metal blinds and faux wood blinds, a remote-controlled system will do nothing more than tilt the slats or vanes. It will not lift the blind up or down. For blinds such as woven woods or sheers, it will just lift it up or down. Remote blinds are available for both options.

Most are operated by a remote control, but customers can use an optional wall switch to operate the electric blinds. Some remote controls can operate up to five different channels, which will usually be enough for your entire home or office.

Design and implementation
According to the WBDG, the design of effective shading devices will depend on the solar orientation of a particular building facade. “Simple fixed overhangs are very effective at shading south-facing windows in the summer, when the 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.” 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,” the WBDG cites.

The WBDG states that exterior shading devices are particularly effective in conjunction with clear glass facades, but architects can also use high-performance glazing that has very low shading coefficients. When specified, these glass products reduce the need for exterior shading devices.

The guide offers advice on how to properly apply shading devices. “It is necessary to understand the position of the sun in the sky during the cooling season. The position of the sun is expressed in terms of altitude and azimuth angles. The altitude angle is the angle of the sun above the horizon, achieving its maximum on a given day at solar noon. The azimuth angle, also known as the bearing angle, is the angle of the sun’s projection onto the ground plane relative to south.”

A shading device 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 the shading devices are considered, the more likely they are to be attractive and well-integrated in the overall architecture of a project.” The WBDG further states that the degree of window shading is a major consideration. “Both the projection factor for exterior shading and the shading coefficient of glass must be evaluated when using an alternate component package envelope design approach.”

The guide specifies that architects should 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, one should limit the amount of east- and west-facing glass since it is harder to shade than south-facing glass. Consider the use of landscaping to shade east and west exposures.”

The WBDG further cites that shading effects day-lighting. An architect should consider both simultaneously. “For example, a light shelf bounces natural light deeply into a room through high windows while shading lower windows.”

For architects to successfully design and use sun-control systems, the studying of sun angles is highly important. “An understanding of sun angles is critical to various aspects of design, including determining basic building orientation and selecting the appropriate shading devices.” Shading strategies that work well at a certain latitude, may be completely inappropriate for other sites at different latitudes. “Be careful when applying shading ideas from one project to another.”

Durability and maintenance issues are also a concern, but using the correct product and design with expert technical backing will ensure an installations success.

Full acknowledgement and thanks are given to WBDG, RVI and Hunter Douglas for the information given to write this article.