A BRIGHT FUTURE: The Role of Channel Glass in Daylighting
By Tysen Gannon
From the start of civilization, people have tapped the sun as a source of light. Thousands of years ago, Egyptians were among the first to develop a sophisticated understanding of the power of sunlight. They developed lattice work to filter light, and constructed their buildings in precise locations to align with the sun’s position.
Each succeeding society has added new knowledge and creative thinking about how to use solar power to light interior spaces. The Romans introduced glazed windows, vaulted ceilings and arches. Later civilizations perfected the use of clerestory windows and skylights.
Then came the 1970s – the “Dark Ages” of building design. Theories changed dramatically regarding the sun. Big windows were viewed as energy drains. To create more energy efficient buildings, architects moved to the “concrete box” model. Artificial light replaced natural light wherever possible.
Fortunately, the pendulum has once again swung the other way. Today, architects are using the latest science and technology to harness natural light, creating spaces that are not only energy efficient, but also comfortable for occupants and aesthetically pleasing.
Daylighting has come into its own. More than ever before, we are learning how to take full advantage of sunlight’s benefits while minimizing its drawbacks. With the renewed emphasis on green building and LEED certification, the use of daylight has become a vital component in design.
Simply put, the word “daylighting” can be defined as the use of natural light to illuminate a building. For some people, the term daylighting conjures up images of expansive windows in direct sunlight, but that is a misconception. Direct sunlight is generally too strong to be used in daylighting, since it can create glare and oppressive heat gain.
Reliance on direct sunlight is also limited because it offers spotty coverage -- illuminating portions of a space while leaving others dark. Good daylighting practices achieve a more diffuse, evenly spread light. The goal is to determine how to bring natural light to all occupied rooms in a building – whether or not they have exterior views.
Daylighting benefits construction on many levels. From a human resources perspective, natural light has been shown to enhance worker productivity. For example, one study conducted by the California Energy Commission showed that call center workers with outdoor views performed 10 to 25% better on tests of mental function and memory recall than their counterparts with no view.
Students also thrive in natural light. More than 8,000 elementary age students participated in research conducted by the Heschong Mahone Group. Over the course of one year, students with the most daylight in their classrooms progressed 26% faster in reading and 20% faster on math tests than students with the least daylight.
From jails to shopping malls, nearly every human environment benefits when the element of natural lighting is introduced. Morale, productivity, concentration and health all show signs of improvement.
There are more concrete, tangible benefits to daylighting as well. The old myths that daylight is too expensive and an energy drain simply have not proven to be true. A well-planned daylighting strategy has the potential to reduce costs rather than raising them. When properly channeled, natural light generates very little heat and can in fact cut down air conditioning bills. Done right, daylighting is good for the bottom line.
What’s more, daylighting is a sound environmental practice. It has been described as the most environmentally responsible lighting technique available and a vital component of the green build initiative. Joel Loveland, director of the Integrated Design Lab in Seattle (a daylighting laboratory), says that a building can get halfway to a LEED certification simply through good daylighting. Well-designed facilities can use daylighting to greatly reduce the amount of energy needed for lighting and climate control.
To the casual observer, the logical way to increase daylighting seems like it would be to just increase the number of windows. However, in an effectively daylit building, windows typically comprise no more than 25 to 40% of the wall area.
Rather than expanding the windows, architects are turning to less traditional glazing materials to meet their daylighting needs. One increasingly common example is found in channel glass. Channel glass is made of long, narrow, U-shaped channels of glass that interlock. It can be installed vertically or horizontally, and it only requires a very narrow aluminum frame around the perimeter.
The reason channel glass works so well for daylighting is that it diffuses the light. The glass has varying degrees of translucency, allowing light to pass through while maintaining privacy. Rather than allowing harsh direct sunlight through, channel glass softens the light as it enters a space.
Often, daylighting requires windows to be high up on a wall for optimum positioning. Channel glass allows for uninterrupted vertical spans that stretch as high as 23 ft. Curved walls are also possible.
Channel glass was recently incorporated in the Seminar II building at The Evergreen State College in Olympia, Washington. With a climate known for overcast skies most of the year, school officials wanted a building that would make the most of available natural light.
Designed by Mahlum Architects, Seminar II is made up of five semi-independent buildings that serve a variety of needs: work spaces, classrooms, lecture halls and offices. From the start, the architects knew daylighting would be a prominent factor in the design of the complex.
Several daylighting strategies were implemented: Light wells, skylights, overhangs and even landscaping were carefully selected for optimum results. Channel glass was installed in all of the four-story stairwells. In that space, the glass created an open feel and greatly reduced the need for artificial lighting.
Any time such large amounts of glass are in a building’s design, thermal performance will be a key. Glazing can act like a giant magnifying glass, concentrating heat where it is least wanted. Similarly, during cold winter months, heat can rapidly escape through uninsulated glass.
Heat gain and heat loss can be controlled in channel glass through an innovative insulating material called aerogel. Since it is 90% air, aerogel is translucent. Considered the lightest weight and best insulating solid in the world, aerogel works well in daylighting applications.
Uninsulated channel glass has an R-value of 2. With aerogel insulation, that same channel glass can have a much improved R-value of 3.5. Additionally the solar heat gain coefficient drops from .69 to .42.
At the John C. Lincoln Hospital in Phoenix, the emergency room waiting area featured a channel glass wall along one side. While beautiful to look at, the glass baked in the desert sun. Inside the waiting room, the temperatures could get unbearably warm. Yet keeping the heat down was increasing energy costs.
The solution was simple: retrofit the dual glazed channel glass was aerogel insulation. Comfort improved dramatically, and so did air conditioning costs. The insulation made a noticeable difference for staff and patients alike.
By allowing diffuse light in and keeping unwanted heat out, channel glass can be a tremendous asset in designing for daylighting. With a variety of textures and colors, long lengths and flexible performance, channel glass has a bright future ahead of it.
Tysen Gannon is the product manager for Pilkington Profilit™, a channel glass offered by Technical Glass Products (TGP), Kirkland, Washington. www.tgpamerica.com, (800) 426-0279
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