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Viewing building systems as integrated packages instead of individual products is a method that will help any facilities manager achieve operational efficiency. And, as a growing number of professionals grasp this reality, a change in thinking is occurring industry-wide.
With exterior façades historically viewed as an autonomous building component, there is now a growing interest in designing, analyzing, procuring, and operating a façade as part of a system. According to Lawrence Berkeley National Laboratory’s Building Technologies Program Head Stephen E. Selkowitz, Berkeley, CA, a façade system delivers the greatest performance when it becomes an essential part of a fully integrated building design.
Focusing on façades that utilize daylighting, sun control, ventilation systems, and dynamic systems, the Lawrence Berkeley National Laboratory (LBNL) conducted a review of high-performance façades to better understand their capabilities and limitations. The review’s primary goal was to explore and define façade performance for California building owners so they could make informed decisions in terms of energy efficiency, ventilation, productivity, and sustainability. But, as the LBNL found, when properly designed and executed as part of a complete building system, high-performance façades can provide solutions to many of today’s national challenges in building design.
What is a High-Performance Commercial Building Façade?
According to Selkowitz, high-performance commercial building façades are comprehensive systems that incorporate daylighting, solar heat-gain control, ventilation, and space conditioning.
Typically, high-performance façades provide:
- Enhanced sun protection and cooling-load control, increased thermal comfort, and ample daylighting.
- Improved air quality and reduced cooling loads using natural ventilation schemes, employing the façade as an active air-control element.
- Reduced operating costs via daylighting-thermal tradeoffs, minimizing lighting, cooling, and heating.
- Improved indoor environments leading to enhanced occupant health, comfort, and performance.
These façade systems also respect the limits of latitude, location, solar orientation, acoustics, earthquake and fire safety, etc. And, since climate and occupant needs are dynamic variables, the façade must have the capability to respond and adapt to these changing conditions.
What follows is a summary of available high-performance building façades and some points to consider regarding these systems.
Spectrally Selective Solar Control
Spectrally selective solar control is window glass that permits some portions of the solar spectrum to enter a building for daylight purposes while blocking others associated with the transmission of solar heat. Microscopically thin, low-E coatings control solar heat gains in summer, prevent loss of interior heat in winter, and allow occupants to reduce electric-lighting use; these systems significantly reduce energy consumption and peak demand. Newer glazings have a clearer appearance, admit more daylight, and permit brighter, more open views to the outside. These glazings can also be combined with other absorbing and reflecting glazings to provide a range of sun-control performance.
Applicable in both new and retrofit construction, spectrally selective glazings benefit buildings in warm and cold climates. The technology is most cost-effective for facilities with large cooling loads, high utility rates, poorly performing existing glazing, or for facilities located in the southern United States. In the northern United States, the systems can be cost-effective for buildings with both heating and cooling requirements.
In general, the technology has a 3- to 10-year payback in commercial buildings where it replaces clear single-pane or tinted double-pane glass, and in most commercial buildings in the southern United States where it replaces conventional high-transmission, low-E, double-pane windows.
Solar filters (such as overhangs, fins, light shelves, or secondary exterior skins made of filter material) indiscriminately absorb or reflect a portion of both direct and diffuse solar radiation and are applied to south-, east-, or west-facing exterior walls to cut down on solar radiation levels and diffuse daylight. The filter materials in secondary exterior skins are made with an opaque-base material (woven or perforated, metal or fabric) or transparent-base material (etched, translucent, or fritted glass or plastic).
Initially, these filters were used in non-view portions of the roof or window wall. Now, however, there is an increased tendency to use filters in the view portions of the window wall for aesthetic purposes; but, this can impair views and increase glare, since the window luminance within the direct field of view is significantly increased. Perforated blind systems can provide solar control with daylight admission and can also improve visual comfort through the reduction of the luminance contrast at the window.
Exterior Solar Control
The general concept of exterior solar control is to stop direct sun from entering the building. Exterior solar control can be provided by overhang, fin, or full window-screen geometries. Exterior solar control should be designed to intercept direct sun when cooling-load control is desired.
Some examples include louvers and blinds; they are composed of horizontal or vertical slats. Exterior blinds are more durable and made of galvanized steel, anodized or painted aluminum, or PVC for low maintenance. With different shapes and reflectivity, louvers and blinds are used not only for solar shading, but also for redirecting daylight. While fixed systems are designed mainly for solar shading, operable systems can be used to control thermal gain, reduce glare, and redirect sunlight. Operable systems (whether manual or automatic) provide more flexibility, responding to outdoor conditions.
These systems perform well in all climates. For commercial buildings in hot climates, the system may be more energy efficient if placed on the exterior of the building while blocking solar radiation. For buildings in cold climates, the system can be used to provide more daylight and absorb solar radiation.
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