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Fenestration Forum: October 2012

Our last column outlined some of the complexities involved in capturing natural light to illuminate buildings.

Our last column outlined some of the complexities involved in capturing natural light to illuminate buildings. We also learned that when buildings are properly illuminated using natural light operating costs may be reduced in some cases.

In the past, illumination engineers were often restrained from using natural daylighting primarily because of the perception that operating costs associated with additional heating and cooling loads might increase. However, the relatively recent innovations in high-performance windows and glazing have resulted in improved energy performance. When combined with advancements in daylighting controls, engineers can now take a more practical approach to harnessing natural illumination. The net result has been a reduction in our dependency on electrically powered lighting.

 Effective daylighting requires a systematic approach. No single design approach can be applied to all buildings. Retrofitting daylight strategies for existing buildings does present a challenge primarily because it is not possible to change the building’s orientation.

However, a careful study of the building’s fenestration components may still present attractive retrofit solutions. Illumination engineers now use computer programs extensively to effectively model and simulate daylighting systems prior to construction or modification.

Although not every element contained in the following list is considered absolutely essential, the systems that engineers now develop for new buildings typically have one or more of the following features:

• a building orientation that takes advantage of the potential for natural illumination
• a window-to-wall ratio appropriate for the climate
• high-performance glazing
• passive or active skylights
• tubular daylighting devices
• solar shading components
• responsive electric lighting controls

In most cases, daylighting systems will function more effectively if daylighting components are equipped with redirection devices.

Natural illumination can also be enhanced by proper choice of interior design features and surface finishes. In addition to properly placed windows and skylights, light tubes and light shelves can also be effective in maximizing the amount of daylighting that can penetrate deeper into the building. Not only is the available natural light subject to a fair amount of variability, but the occupants’ need for light, whether natural or artificial, also changes depending on their activities inside.

 Designers, engineers and building owners are continuing to demonstrate interest in the potential benefits of daylighting on an international scale. To integrate daylighting strategies properly, all the stakeholders including the building owner, architect, lighting designer, HVAC engineer, interior designer and operational staff should be involved. In commercial buildings, the work environment needs to be assessed on a room-by-room basis under ideal circumstances to ensure adequate illumination for the tasks that will be undertaken. There also needs to be a degree of control over the system by occupants because experience has shown that workers will insist upon it.

Illumination engineers have learned from experience that daylighting strategies that are properly designed and installed to ensure even lighting distribution, have controls to limit glare and/or heat gain without creating visual distractions can generally have positive effects on building occupants and building operation.

They have also discovered that if these rules of thumb are not considered, daylighting has the potential to create negative effects. Proper commissioning of the systems and regular maintenance are important considerations.

Brian Burton is the author of Building Science Forum and is serving on CSA’s Fenestration Installation Technician Certification Committee. Brian is a research and development specialist for Exp (The new identity of Trow Associates).
He can be contacted at brian.burton@exp.com or through www.exp.com.