Insulating Glass Units

Insulating units are two or more panels of glass bonded to a perimeter spacer material with a hermetically sealed airspace. The primary benefit is to improve thermal performance with better U-factors as well as solar control by influencing the Solar Heat Gain Coefficient (SHGC). All types of manufactured glass can be fabricated into an insulating glass unit. Coatings can be added in between the two panes of glass to adjust and fine-tune its overall properties according to project needs. Double glazed units are the most commonly used type of insulating glass unit, however in some climates, the use of multi-cavity, triple-glazed units is increasing in response to owner demands and tightening energy codes.

Coated Glass

Sometimes, there is a desire to add a coating onto one or more glass surfaces to improve the physical characteristics of the glass. There are two different ways to add coatings to glass.

• Sputter coating is a low-pressure technique that deposits a coating using a physical vapor deposition (PVD) method. Essentially, it uses a sputtering target that ejects material onto a substrate─in this case, the glass. This process is used in many industries, including computers and semiconductors. For glass, it can be done readily by fabricators since it does not require applied heat or unusual equipment.
• Pyrolytic coatings are incorporated into the glass by depositing microscopically thin layers of metallic oxides during the manufacture of float glass using a process known as chemical vapor deposition (CVD). Such coatings need to be applied by the manufacturer, but fabricators can purchase the pre-coated glass and use it to create other products. Having this type of hard pyrolytic surface fired at over 640°C (1200°F) makes pyrolytic products more durable than sputter coating. The pyrolytic process creates extremely durable coated products that can easily be handled, transported, and processed. In addition, because the pyrolytic surface doesn’t degrade like a sputtered coating, it can be warehoused locally for availability, reducing project lead times.

Coatings can be used to create glass with alternative visual properties such as color, opacity, light reflection, and absorption. Where needed, coatings can also produce low emissivity, solar control, and even self-cleaning properties. One common coating is “low-e” or low-emissivity coating for thermal purposes. This type of coated glass provides thermal control and enhanced insulation, as well as control of solar heat gain. Low-e coatings reduce the emissivity of the glass surface, meaning the glass provides greater insulation by reflecting heat back towards its source and can also be designed to absorb or reflect solar energy. As such, low-e coatings are useful for reducing both solar heat gain and heat loss. For a sense of context, uncoated glass has a typical emissivity of 0.84, while a low-e coated glass could have an emissivity of 0.15. This means only 15 percent of heat is absorbed and reemitted, while the rest is reflected. Different combinations of low-e coatings can be used in an insulated glass unit to provide the desired performance. Keep in mind, however, that low-e coatings, like most others, will have an impact on the color and amount of light transmission through the glass.

Bending Glass

While annealed glass is manufactured in flat sheets, some fabricators have the capability to bend and form glass in their facilities. Fabricators can form the flat sheets into a curved shape or profile using extreme heat and a mold or frame. This is most commonly done along a single axis, such that the sheet is curved in one dimension while the other dimension remains stable. In this manner, balustrades or other surfaces can take on shapes such as half-cylinders, waves, “s” shapes, or other curved appearances.

When a building design requires it, glass can also be bent into compound shapes, meaning both axes are impacted. Fabricated compound shapes can include conical sections, segments of spheres, ribbon twists, and even amorphic shapes─the only limitations are those imposed by the physics of the glass itself. The glass may be placed under heat and “slumped” over a mold in this case. Since these are clearly more complex and involve glass engineering as well as fabrication, collaboration between designers and fabricators is encouraged early in the design process in order to assure the design can actually be created at a cost within the budget.

All types of bent or curved fabrications can be made from annealed, heat-treated, or tempered glass and further fabricated into laminated or insulated units. They can also incorporate a variety of other features such as chemical strengthening and decorative treatments. These performance attributes make bent or curved fabrications suitable for a wide range of potential uses including exterior windows, curtain walls, store and mall fronts, custom residential glazing, interior partitions, display cases, cylindrical elevator enclosures, and skylights. They can also be used for decorative and artistic installations made of glass.

LAMINATED GLASS PROJECT EXAMPLE

Project: Aquarium of the Pacific
Location: Long Beach, California
Architects: Esherick Homsey Dodge and Davis (EHDD)
Photography: Courtesy of Pulp Studio

The Project: The glass fabricator produced 800 unique panels of a special, triple-laminated glass to comprise the facade on the new wing of the Aquarium of the Pacific in Long Beach, Calif. The project was featured in the Architect’s Newspaper. It also won Best Decorative Glass Application–Exterior by Glass Magazine.

IMAGING TECHNOLOGIES ON GLASS

A common and growing design trend is to use glass as a material for graphics, imaging, signage, artwork, or other visual displays. Glass fabricators are able to provide such products as well, using a variety of technology options including the following:

Ceramic Frit

While this technique has been popular for architectural glass in the past, it is mostly used only for signage currently. The process involves permanently bonding a pattern of ceramic-based material onto the surface of glass. This has the benefit of durability, but its cost-effectiveness is limited to large projects with repeating patterns. Ceramic frit has some inherent limitations, too, namely a very limited choice of colors and significant size restrictions. It is also not favored if there are a lot variations in the pattern.

Flatbed Printing with UV Inks

An alternative to surface-applied frit is to print a pattern or signage directly onto the glass using UV inks. Note that these inks are cured with ultraviolet light (UV,) but that doesn’t mean they are UV-stable over time once they are installed in a building, particularly if they are exposed to sunlight. This process involves placing the glass onto a flatbed printer just like any other media that might be used on such a printer. The ink is applied with a print head that moves back and forth (similar to many common printers). The ink adheres to the glass, but it is not chemically bonded to the glass the way a frit application is. This limited adhesion makes the process suitable for signage but not for architectural elements. In some cases, though, it may be appropriate to print on the back side of the glass (i.e., #2 surface), allowing the printed image to be protected by the glass. In either case, the size of the printed area will be limited due to the size of the printer, further suggesting its preferred use for small graphic panels or signage.