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1. What are the benefits of using external shading systems?
Improved HVAC efficiency: Exterior shading systems block solar heat gain before it enters a building through the glazing. The reductions in solar heat gain put less load on HVAC systems and save costs associated with running those systems. The efficacy of external shading at managing solar heat gain is significantly higher than many interior solutions, blocking 95 percent of solar energy. By contrast, interior solutions may block only 60 to 75 percent of solar energy.
Natural daylighting: External shading system can optimize the use of sunlight to illuminate interiors, reducing the need for artificial lighting. Interior comfort: A well-designed shading system contributes to comfortable working conditions, managing both heat and glare while providing access to views of the outside.
Aesthetics: Using exterior shading systems can make a significant contribution to the appearance of the building.
2. Can exterior shading solutions be used on both new and existing buildings? What are common methods of attachment?
External shades can be applied to existing buildings, as well as new ones. While pre-existing buildings may not have been designed to accommodate exterior shading, structural elements can be added to support installation onto the existing facade. The structure could then handle any loads from wind/ ice/snow, as well as the weight of the system itself. In the case of either a new or an existing building, installation a system might attach directly to curtainwall mullions, to brick or block work, or through cladding to the structure. Requirements vary by product type:
- Exterior roller shades and venetian blinds generally install in front of the glazing and do not apply significant loads to the facade. They will retract when wind speeds exceed a defined level. Pre-tensioned side-guide wires are used to prevent movement of the shading system under wind load.
- Exterior louver systems and brise soleil systems place more significant loads on a building. These systems usually remain in place in all weather conditions and must withstand loads for wind and other factors as defined by local building codes. Likewise, the building façade needs to withstand the loads these systems transfer to the structure-this might mean, for example, that mullions need to be reinforced with steel.
3. What external solutions should be considered for the most common shading challenges?
Choices for external shading solutions include fixed panels of louvers (brise soleil), adjustable (motorized) sun louvers, and retractable/operable shades (external venetian blinds and roller shades). Most exterior louver systems and brise soleil systems are fixed and do not adjust in response to sun position or weather changes. They usually install horizontally, either above or in front of the glazing. They are most effective on south-facing elevations, but can also be effective on east/west elevations.
Exterior roller shades and venetian blinds also provide effective shading on any façade, but have the advantage of being retractable if desired. For example, they are designed to retract if wind speeds are too high. Due to wind concerns, they are generally used on buildings up to 12 floors in height.
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4. Are shading systems more effective in certain areas?
Counterintuitively, buildings farther north tend to require more shading, because low sun angles cause problems with glare and heat gain that can be difficult to address. By contrast, in a southern location such as Miami, sun angles are high (~86º above the horizon) and a small building overhang and interior shades can block heat and glare.
5. What fact ors are important to consider when specifying exterior shading?
The heating/cooling cycles of the building are important to consider. In cold climates, it may be desirable to allow solar heat gain in winter, while blocking it in summer. In such cases, exterior roller shades or venetian blinds would be preferable to fixed louver systems.
The design team should also consider material selection. Many systems utilize aluminum, due to its strength in comparison to weight, ability to be shaped and perforated, and wide range of finish options, from painted finishes to wood-look powder coating, and more. Other materials include glass and wood. Glass requires more support structure, and glass louvers must be fritted or sand-blasted to provide shading, a process that reduces their transparent look. Wood is susceptible to fading, warping and cracking, so may require more maintenance over time.
Engaging a company with experienced design/engineering capability is critical, perhaps more important than the specific shading product(s). Finding specialists in external shading will ensure the solution will be effective and remain reliable. Further, decisions about external shading are best made early on, because these systems are integral to the building design. Selecting and evaluating systems at the start of a project will allow time for modeling performance, addressing attachment challenges, and considering other factors (such as wiring of operable systems).
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Richard Wilson is the director of the advanced technology group for Hunter Douglas Contract Solar Control, Nysan Solar Control, El Monte, Calif. For more information, visit www.hunterdouglascontract.com.