As seen in Glass Canada, February 2009
Northern Lights
Daylighting Options Expand with Channel Glass
By Jeff Razwick
With a cool climate and most of its land closer to the North Pole than the equator, many may overlook the strong opportunities for using daylighting designs in Canada’s buildings. However, architects, glaziers and other building professionals can take advantage of daylighting benefits that are commonly realized in more southern locations.
Daylighting is deliberate and integrated design strategies that use sunlight to illuminate interior spaces. The goal is to reduce energy use and improve people’s productivity and sense of well being. Building owners and employers, in turn, receive substantial monetary benefits.
According to the “Daylighting Guide for Canadian Commercial Buildings” published by Public Works and Government Services Canada, several factors make Canadian buildings well-suited for daylighting. First, Canadians spend much of their time indoors due to weather. Second, daylighting works best with diffuse, rather than direct, sunlight. Because most daylight in Canada is diffuse, this helps overcome challenges with heat gain/loss and glare.
Illumination from the sun is sufficient for daylighting in all but extreme northern areas of the country where short days prevail for extended periods. At 46 degrees north latitude – where most people live – average solar lighting under overcast skies is about 15 times greater than required for typical indoor tasks.
The keys to effective daylighting are to capture sufficient natural light, while avoiding the problems of too much light. While daylighting design guides frequently discuss the use of various classes of window glazing, alternate glazing materials now available in North America are expanding the options.
Notable among these is channel glass. Its unique properties provide a clear way to overcome the challenges of daylighting in cold climates.
Daylighting Benefits
A range of studies detail the benefits to building users and owners from daylighting. The “Daylighting Guide for Canadian Commercial Buildings” summarizes the advantages as:
- Improved lighting quality
- Better occupant comfort and health
- Increased productivity and retail sales
- Reduced auxiliary lighting load
- Reduced cooling load
- Reduced peak electricity demand
People respond better to full-spectrum natural light than the artificial light created by incandescent or fluorescent lights.
Joel Loveland, director of the BetterBricks Daylighting Lab, notes a number of health benefits. Hospital patients recover more quickly, and babies in neonatal intensive care units grow faster and are released sooner when exposed to brighter illumination during the day.
In studies of office and call center workers, the Heschong Mahone Group found that those with outdoor views performed up to 25 percent better in memory recall and mental function than those without views. Daylighting has a similar benefit for students. Those with the most daylight in their classrooms advanced 26 percent faster in reading and 20 percent faster in math than students with the least daylight.
For retailers, the potential for increased sales is also substantial. Another Heschong Mahone Group study reported increased sales of 6% in one retail chain for its daylit stores.
In addition to the human benefits, daylighting provides energy savings – helpful to both the environment and for reducing building operating costs.
Daylighting expert Gregg D. Ander of the Southern California Edison Company reports that daylighting can reduce total energy costs for commercial buildings by up to one third. Savings come from reduced reliance on electric lights, less need for heating on colder days, and diminished cooling system requirements to offset waste heat from artificial lights.
One example from an article in The Construction Specifier magazine describes how daylighting reduced lighting costs by 75% and total energy demand by $500,000 (US) per year for a 56,000 square-metre office building owned by the Lockheed Martin Company.
Daylighting Challenges
Effective daylighting requires more than adding windows. It’s a careful balance between capturing light, managing glare, and supplementing illumination with controlled artificial lighting. Plus, for climates like Canada’s, addressing heat loss through the glazed area is crucial.
Direct sunlight can distract building users and offset the benefits of receiving natural light. Glare on windows and computer screens is particularly annoying. Likewise, direct sunlight can raise interior temperatures uncomfortably or require additional costs for cooling. Designers can overcome these problems with building design and placement, automated systems, and selection of construction materials.
According to the BetterBricks Daylighting Lab’s Joel Loveland, designers can take a number of actions to capture natural light while avoiding glare and heat gain/loss:
- Provide windows to all occupied rooms, either directly to the outside or opening to sunlit interiors
- Pay particular attention to east and west facing windows, which produce the most intense glare – southern and northern exposures are preferred for diffuse light
- Incorporate translucent glazing to help diffuse light on bright days
- Use reflective surfaces to maximize the impact of natural light
- Install shutters or blinds to block midday sun
- Utilize light pipes to bring sunlight into dark areas
In addition, achieving the energy savings from reduced lighting requires coordination between glazing design and lighting control systems. If a building captures natural light but doesn’t have automated systems to reduce artificial lighting, the result can be a net increase in costs due to higher cooling demands.
For winter months, in particular, the glazing must also be designed to reduce heat loss since glass tends to transfer heat at a higher rate than other building materials such as wood and concrete.
Advent of Channel Glass
Many design professionals are accustomed to using specialty glazing for daylighting applications. High-performance, energy-efficient windows help lower heat gain/loss. Coatings, films and tints can diffuse light and reduce glare. At the same time, more daylighting designs rely on alternatives to traditional window glass.
For example, channel glass is increasingly being used given its unique abilities to fulfill daylighting needs.
Channel glass systems, such as Pilkington Profilit™, consist of self-supporting “U”-shaped cast-glass channels mounted in an extruded metal perimeter frame. The channels come in lengths up to 7 metres and can be installed vertically or horizontally. In vertical installations, channel glass typically does not require intermediate mullions.
The framing system and narrow glass channels allow formation of straight walls, or curved and serpentine walls with tight radiuses (as low as 2 metres). These various properties enable designers to create large, uninterrupted areas of glazing for interiors or exteriors, which works especially well for capturing daylight.
In addition, channel glass performs very well on one of the specific window placement recommendations identified in the “Daylighting Guide for Canadian Commercial Buildings:” using strip windows for uniform office lighting. An uninterrupted span of glazing provides sufficient lighting to a room without contrasting shadows as is typical with individual window openings.
Channel glass is also available in a variety of colors and textures with varying translucency, allowing for the passage of natural light without the loss of privacy. It provides warm, diffuse light for interior spaces without glare.
Channel Glass and Energy Efficiency
The configuration of channel glass systems helps them reduce heat gain/loss. The individual glass channels are mounted in an overlapping fashion, creating an insulating air-filled space. Thermally broken frames are also available to reduce heat bridging. The U-value of the glazing and framing system is 0.53. The glass is also available in a low-E variety with a system U value of 0.42.
To further enhance energy performance, insulating aerogel can be placed in the enclosed space between the channels to reduce the system U-value to 0.32. Products such as Nanogel® aerogel are translucent and helps promote soft, even light dispersion, while reducing condensation and unwanted noise. This advanced material is sometimes called “frozen smoke” since it is one of the world’s lightest solids.
Channel glass systems have been used in Europe for more than 30 years, where they have performed very well in cold, northern climates.
Conclusion
Realizing the benefits of daylighting does not need to be difficult, but does require careful planning. Numerous design guides are available in print and online, and professional courses are available to learn the nuances. As you design with or make recommendations to others on daylighting designs, remember that alternative glazing systems may be especially suited for your specific design challenges.
Jeff Razwick is the Vice President of Business Development for Technical Glass Products (TGP), a Kirkland, Washington-based supplier of fire-rated glass and framing systems, along with specialty architectural glass products. www.tgpamerica.com, 800-426-0279
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