As seen in Construction Canada (December 2010)
Channel Glass: Design Options for Natural Light and Esthetics
By Jeff Razwick
Channel glass and Mother Nature
The aftermath of Hurricane Andrew was severe, resulting in more stringent building codes that emphasized protection of the building envelope. While
important to the safekeeping of people and property, such mandates limited glazing options. For instance, many approved glazing systems have protective
glass films, which, according to the National Institute of Building Sciences, Washington, can block out too much daylight and produce excessive
exterior reflectivity. Further, glazing applications often require supplemental protective devices like shutters that can hinder sleek visual lines.
Recently, however, a hurricane-approved channel glass system entered the market. The system consists of dual-glaze, vertically oriented, cast-glass
channels with a polycarbonate laminate and thermally broken frame. The channels can extend up to 305 cm (10 ft) high and are approved for 293 kg-force
m2 (60 PSF) design loads.
The system meets Miami-Dade County and state of Florida requirements, which are among the most stringent codes in North America for protecting
buildings against high-wind and wind-driven projectile damage.
The end result is a system that protects against high winds and wind-borne debris, yet can transfer diffuse natural light in high-end designs.
Although the Canadian climate is colder and receives less sunlight per year on average than other parts of North America, there is sufficient natural
light for effective daylighting in commercial buildings.
A curved channel glass wall combines interesting lighting effects and visual separation between lobby and entry drive in a luxury hotel.
The Daylighting Guide for Canadian Commercial Buildings points out that the majority of Canada's population lives near latitude 46 degrees. 1 At this latitude-even under overcast skies-it is possible for interior spaces to receive fifteen times more illumination than is required
to perform typical indoor tasks.
Channel glass systems are well suited to take advantage of available sunlight in such conditions. Their U-shaped, cast-glass channels and extruded
perimeter frame allow for large glazed areas that can diffuse extensive amounts of natural light deep into interior spaces without glare or excessive
shadows, while reducing heat transfer.
In addition, such systems can contribute to building envelope performance without detracting from contemporary design. The growing demand for
sustainable buildings can cause architects and building professionals to concede on aesthetic design goals in favor of energy-, water- and
pollution-saving applications. Channel glass, however, allows architects to create sophisticated designs while supporting green building goals such as
daylighting and managing a building's energy consumption.
A channel glass system with custom mounting clips provides a varied façade and supports ventilation in a multi-story parking garage.
Daylighting in northern latitudes
Rain, snow and harsh weather force many Canadians indoors for extended time periods. As such, the benefits of channel glass' balanced light
distribution can help combat sun-dependant mood disorders, diminished workplace productivity and spikes in electrical lighting loads and costs.
Diffusing light
A primary advantage of channel glass is its ability to diffuse natural light into interior spaces. The channels spread out the sun's rays as they pass
through its translucent surface, creating soft, even and glare-free light, with fewer and less sharply defined shadows than traditional glass and
framing. By dispersing light, such systems help prevent bright spots on computer screens and reflection from other interior shiny surfaces, as well as
spotty illumination during the sun's peak hours and long shadows during the winter. Less focused light can also help reduce heat build up.
In addition to diffusing light, channel glass has a high visible light transmittance (VLT). The VLT for uncoated, double-glazed applications ranges
between 70 and 75 percent, allowing occupants to receive the benefits of natural light. Full-spectrum sunlight imparts a mixture of colours and gradual
illumination changes throughout the day that artificial lights typically cannot replicate. As studies show, this can enhance worker productivity,
student learning, and even boost retail purchases. 2
Building professionals desiring even greater light transmittance can select from low-iron oxide channel glass systems. Cast-glass channels with lower
iron content are available with a VLT greater than 90 percent.
A parking garage in a busy city uses variably spaced channel glass panels to add dimension to its exterior.
Offsetting heat gain and loss
While sunlit interiors can enhance building occupant comfort and reduce the required amount of electrical lighting, they can also lead to excessive
heat gain-or loss, as is common in colder climates. Glazed lites often have a lower thermal performance than surrounding building materials. Channel
glass' unique configuration helps combat the heat exchange dilemma. The individual cast-glass channels are mounted in an overlapping fashion, creating
an insulating dead air-filled space and thermal gap. The result is a solar heat-gain coefficient of 0.70 and a U-value of 0.49.
To further improve energy efficiency and reduce thermal bridging, building professionals can specify channel glass with thermally broken frames and
insulators. For instance, adding insulating areogel, which is 90 percent air and therefore translucent, and low-E coatings, can reduce the solar
heat-gain coefficient to 0.31 and the U-value to 0.21 with marginal impacts on light transmission.
Designing for success
To reap the benefits of channel glass in the Canadian climate, it is critical to examine what design solutions best fit the local environment. The Daylighting Guide for Canadian Commercial Buildings notes that increasing the glazed area is one effective daylighting solution in areas prone
to overcast skies, as the light is more diffuse and therefore easier to control. Since channel glass systems can extend for up to 7 meters (23 ft.) in
length without interim framing, as well as be stacked over floor slabs to achieve greater heights, they are well suited for such applications.
When installing oversized applications, it is important to consult with the engineer of record to ensure the appropriate measures are being taken to
meet load- and wind-bearing requirements. For instance, in areas subject to strong winds, hurricane-rated channel glass may be more appropriate (see
"Channel glass and Mother Nature").
Another effective daylighting strategy is to use strip windows for uniform office lighting. Here too, channel glass is a suitable option. Since it can
be installed without vertical mullions, the system provides sufficient lighting for occupants without the contrasting shadows and spotty illumination
typical of individual window openings.
Further, as the Daylighting Guide for Canadian Commercial Buildings states that artificial lighting accounts for 30 to 40 percent of
electricity consumption in commercial buildings, it is essential to pair daylighting applications with lighting controls. Doing so can reduce lighting
energy use-and costs-by up to two thirds. 3
Esthetics
Backlit and curved channel glass creates a dramatic ambience for an upscale restaurant.
Channel glass' unique composition, sleek esthetic figure and ability to harness light can be key contributors to the art of building design.
Architects can select from channels that have standard face widths of 232 mm (9.13 in), 262 mm (10.31 in) and 331 mm (13.03 in). The typical flange
height is 60 mm (3.26 in) and typical glass thickness is 7 mm (0.28 in).
While channel glass is frequently installed vertically, architects can vary or intermix the channel orientation for added dimension. Arranging the
linear glass strips in a vertical pattern separated by windows or framing units, can create a contemporary, chic look. Consider the façade of a
mixed-use, residential building. It features a collage of vertically oriented channel glass strips that consolidate the home, workspace and retail
environments in an engaging, yet functional fashion to connect city dwellers to the building. Alternatively, the use of horizontal channels can create
geometrical, form-based walls, partitions and facades.
One increasingly popular trend is to install the cast-glass channels in curved or serpentine applications. While architects can specify traditional
glass in curvilinear shapes, the size of the glass and frame frequently limits the arc of the curve. The slender frames and narrow-glazed segments in
channel glass systems, however, allow for tight radii-as low as 1.9 meters (78 in.). With such compact curves, architects can push the form and shape
of buildings. From cylindrical stairwells to coiling entryways and façades that ripple like fabric in the wind-as does the front of one high-end
retail store using channel glass-translucent channels can evoke landscapes and emotive themes.
Architects can also use the glass channels without vertical mullions for more subtle applications, as well as form glass corners of various angles to
enhance the shape of the building. Custom framing applications are also available to meet specific design needs, depending on the supplier.
Channel glass emulates a flowing dress and nearby coastal landscape in a high-end retail store.
Texture
Channel glass' optical qualities are due largely to its surface texturing, which influences lighting and colour effects. Glass channels are available
with no surface patterning for a clear look, along with a range of textures, such as:
-
Standard (lightly dimpled surface provides moderate level of translucency);
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Micro (finely netted screen surface disperses light in a soft, even manner for greater privacy);
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Macro (netted screen surface delivers moderate to high level of privacy);
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Slim line (thin, linear grooves bend light while obscuring vision); and
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Wave (well-defined ridge texture creates dramatic optical variations)
The range of textures and translucencies can accentuate designs by prismatically bending light and varying its distribution. Intermixing surface
textures within an application can add depth, while incorporating the same texturing throughout creates a more homogeneous look. Wave-shaped channels
offer the most dramatic optical variations and the joints between these channels disappear when viewed laterally. This allows for sophisticated light
play.
Cast-glass channels can also incorporate embedded wire patterns. Longitudinal wires set in the middle of glass strips can help design professionals
achieve custom, decorative walls and partitions. As not all textures and wire in-lays are available in every cast-glass channel size, it is important
to verify desired specifications with the supplier.
Colour
Backlit channels vibrantly change colors at Los Angeles International Airport.
Design professionals can use channel glass to make statements with light and texture-or with surface colour. The standard channel glass cast is a light
seafoam green; additional translucent colours include amethyst, bronze and clear. Such channels provide a hint of surface colour, yet allow for strong
passage of natural light.
For colour-saturated applications, architects can select from a range of standard polycarbonate laminate options and over 1,500-tempered ceramic frit
colours within the RAL design system. With the colour melded to the interior surface of the glazing during manufacturing, coloured ceramic frits are
opaque. Their bold colouring makes them ideal for object architecture and catchy storefronts.
Another design-savvy option is colour-coating metallics. Architects can create one-of-a-kind appearances with the channel's scintillating flecks.
Custom blends are available to help design professionals best coordinate metallics with surrounding colour schemes. Lettering can be applied via decals
or custom painting.
Vertical channel glass glows like a lantern at night.
Where a more obscure appearance is desired, design professionals may wish to consider sandblasted channels. Such treatment achieves greater opacity and
is ideal for spaces like offices, entryways and lounge rooms that require both light and privacy. Typically, sandblasting can only be applied to
standard or clear channels as the procedure removes all coatings. Sandblasted surfaces should be treated with a polymer type coating to protect against
finger and handling marks.
Channel glass systems can also serve as backlit wall sections. Setting lights between the channel glass and the primary thermal wall can create backlit
screens that display one or many colours. Alternating between colours can keep spaces fresh throughout the day, as seen in the Bradley International
Terminal at Los Angeles International Airport. Passengers walk past a terminal wall that shifts between blues, greens and pinks as they head towards
the baggage claim. Conversely, lighted nighttime channel glass installations can become spatial abstractions, acting as beacons of light or landmarks
for customers.
Conclusion
Sweeping spans of channel glass transfer diffuse daylight to interior spaces.
Channel glass expands design options with glazing in a number of high-performance and visually interesting ways. The material is popular in Europe and
is increasingly being specified in buildings throughout North America. It has the advantage of supporting esthetic designs without sacrificing green
building goals.
Notes
http://www.enermodal.com/pdf/DaylightingGuideforCanadianBuildingsFinal6.pdf
on November 20, 2010.
2
Boyce, Peter; Hunter, Claudia; Howlett, Owen; The Benefits of Daylight Through Windows, September 12, 2003, obtained from
here
on November 20, 2010; and Heschong Mahone Group, Daylighting and Productivity, obtained http://www.h-m-g.com/downloads/Daylighting/order_daylighting.htm
on November 20, 2010.
3
See note 1.
Jeff Razwick is the vice president of business development for Technical Glass Products (TGP), a supplier of fire-rated glass and framing systems and architectural glazing. He frequently writes about the design and specification of glazing for institutional and commercial buildings. Razwick can be contacted at jeffr@fireglass.com.
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