Daylighting refers to the intentional and
controlled admission of natural light into a space. A well thought-out daylighting strategy is crucial to maximize the benefits of any daylighting system. Building orientation, unit size and location, lighting needs, glazing material and performance attributes all impact the success of daylighting systems. Effective daylighting creates a more comfortable and visually stimulating environment while immensely impacting the efficiency of the building. Incorporating successful daylighting strategies can reduce the demand for artificial lighting by up to 70 percent, which may account for 30 to 50 percent of a building’s total energy consumption. A reduction in heat generated by artificial lighting also decreases the energy demand on HVAC systems, improving operational efficiency and cost savings.
Achieving a better, brighter building envelope
Not All Systems are Equal
Daylighting systems have been traditionally viewed as a utility product meant to help meet code requirements for introducing natural light into a space. Recent advancements in technology have allowed manufacturers to develop high-performance translucent daylighting systems that can be utilized for the entire building envelope. Manufacturers offer a variety of system options, each possessing different design capabilities and degrees of performance. When selecting appropriate daylighting systems for your projects, it’s important to understand the necessary performance considerations and testing/ code implications to help guide your decision.
Traditional glass façade systems offer transparency and provide occupants with exterior views, but are limited in their ability to effectively control light and reduce glare. They often require external devices such as shades or louvers, and the direct sunlight let in by these systems can result in hot spots, creating an uncomfortable environment for occupants. Translucent systems are better suited for daylighting purposes because of their ability to effectively diffuse natural light evenly throughout a space while also eliminating glare. Using a tightcell extruded glazing panel (cells measuring 0.18 inches) and a matte finish can further enhance the system’s solar performance.
A growing trend is to integrate both system types, dividing the façade into two zones: a viewing zone and a daylighting zone. This maximizes the benefits of each system by maintaining transparency at the ground level while integrating a daylighting system above to better manage the infiltration of natural light and optimize comfort.
Thermal Performance
When designing building envelopes, thermal performance is always a concern. Daylight applications should utilize a two-panel glazing system to achieve the best thermal performance, for the same reasons that double-pane glass is now the industry standard for windows. The internal cavity of most two-panel systems can accommodate additional insulation material for buildings that require greater thermal performance than a standard two-panel system, typically around a U-factor of 0.24 center-of-glazing. There is a tradeoff, however, between thermal performance and light transmittance, as adding insulation decreases the amount of light that the system can let through. The goal is to strike the right balance based on the needs of the building and its occupants.
Longevity and Maintenance
When selecting a daylighting product, especially for a large portion of the building envelope, it’s important to consider the system’s life span and maintenance requirements. Traditional daylighting systems often rely on sealants and adhesives, which break down over time if not properly maintained. Emerging technologies now enable some high-performance systems to mechanically fasten the glazing panels to the internal structure, allowing for expansion/contraction and requiring no maintenance. More importantly, it enables the independent removal of either the internal and external glazing panel without compromising the building envelope. This removable skin technology facilitates panel removal without costly building closures, and essentially prolongs the system’s life indefinitely.
Protection against UV light and glazing discoloration should also be considered. While many systems rely on films or applied coatings, some extruded polycarbonate manufacturers have developed high-performance glazing panels that integrate a UV inhibitor within the chemical make-up of the panel. This provides superior color stability and requires no maintenance.
Versatility and Certification
Some of the more advanced two-panel daylighting systems are designed to be scalable, where the interior cavity can be modified to accommodate specialized building performance requirements. Scalability allows a familiar and trusted system to be adapted for numerous applications. These high-performance systems also provide considerable design flexibility, including custom glazing colors and opportunities to incorporate graphics and backlighting.
To ensure any system will perform as advertised it’s important that the system be fully tested and certified in accordance with relevant building code requirements. The International Code Council has a subsidiary, ICC-ES (Evaluation Service), which provides third-party certification of code compliance for building products. Certifications like this one, along with those provided by organizations like the National Fenestration Rating Council, the International Energy Conservation Code and OSHA, help shift the burden of liability from the designer to the manufacturer. This guarantees performance standards are met so that architects and general contractors can specify products with confidence.
Sam Wheeler is associate creative director of CPI Daylighting, Lake Forest, Ill. For more information, go to www.cpidaylighting.com or call (800) 759-6985.
