New Heat Mirror Glazing for Commercial Applications

Southwall Technologies, the producer of Heat Mirror low-emissivity (low-e) suspended film for windows, and Dow Corning, the leading producer of silicone sealants, announced on November 9, 2010 the availability of a new glazing system that will enable Heat Mirror to be used with structural sealant glazing systems used in large commercial buildings. This opens the door to significantly better energy performance in heavily glazed curtainwall buildings. According to Ron Fillmore, vice president of construction for Dow Corning, “Structural sealant glazing has quickly grown to account for one-third of all commercial glazing.”

The new system combines Heat Mirror “S” (for “structural”) suspended film with a two-component Dow Corning silicone sealant that forms the secondary seal. John Meade, architectural products sales manager for the Southwall Americas, explained to EBN that with a suspended film the secondary sealant used in the insulated glazing unit (IGU) not only secures glass to a glazing spacer, but it has to hold the suspended film in place and keep it taut for the life of the glazing. “We’re asking the sealant to do more,” he explained. And therein lies the challenge.

Until this silicone solution came along, Heat Mirror was most commonly secured to IGUs using polyurethane sealants. This worked fine in window applications where the edges of the IGUs are fully covered (“captured” in glazing parlance), but it didn’t work in structural sealant glazing applications where those glazing panels are butted together. “You’re relying on the sealant to hold the glass in place over its life,” said Meade. In this application, the sealant is exposed to UV light, which degrades organic sealants, such as polyurethane. Because silicone is not an organic material, it is far less affected by UV, so it will maintain that critical bond between film and spacer much longer. This new two-part silicone sealant from Dow Corning, is very fast-curing, while one-part silicone sealant, which has been available in the past, takes more than a week to cure.

Heat Mirror S looks identical to—and has identical glazing properties as—the existing line of Heat Mirror products, but it adheres extremely well to the silicone sealants. The four most popular Heat Mirror glazing options are available in the S designation: HM-88, SC-75, HM-66 and TC-88 (which has the HM-88 coating on both sides of the film). Other Heat Mirror films offered by Southwall could be produced in the S designation by special order, according to Meade.

There are thousands of glazing configurations that can be achieved using different Heat Mirror films, different types of glass (including tinted and low-e), and different overall thicknesses. A few of these options are listed in the table below, along with key performance criteria.

Glazing Performance with Heat Mirror Suspended Films The system is fully compatible with low-conductivity gas fills and meets NFRC-706 certification for durability of IGUs. Glazing panels with the suspended Heat Mirror S film can be up to 79.5" (2.0 m) wide and ten to eleven feet (3.0–3.4 m) long, depending on the fabricator. Costs are higher than those of standard IGUs without a suspended film, but lower and much lighter-weight than all-glass triple-glazed units.

Relative to the weight issue, Meade described a 52-story building in New York City that was to be re-glazed. Triple-glazed (all-glass) IGUs were considered, but that would have added 600,000 pounds (270,000 kg) to the building. This is a widespread issue with triple glazing. “Certainly, one of my concerns with triple glazing is weight,” Don Winston, P.E., the vice president for technical services of The Durst Organization in New York City (owner of the Bank of America Building at One Bryant Place), told EBN. Winston sounded intrigued with the new Heat Mirror option, but would have to be convinced about stability and durability. Bill Browning of Terrapin Bright Green in Washington, DC and New York City, believes this could be a “game changer.”

The first Heat Mirror S glazing will be installed in 2011, and Southwall and Dow Corning are in discussions with a number of glazing and curtainwall companies, which they hope will offer this glazing as a high-performance, lightweight option. The technology is fully tested, according to Meade. “We’re ready to go.”

– Alex Wilson

For more information

Southwall Technologies
Palo Alto, California
800-365-8794, 650-798-1200
www.southwall.com

Dow Corning
Midland, Michigan
800-248-2481, 989-496-4400
www.dowcorning.com

November 10, 2010

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