Among the many topics discussed at this week’s Insulating Glass Manufacturers Alliance (IGMA) Fall Conference in Denver were pressure and inflation. As expected, a certain NFL quarterback’s name wasn’t immune from a mention, either.
Wednesday, Jeff Haberer of Trulite gave a presentation on insulating glass units (IGUs) at high altitudes, discussing the physics of IGUs, pressure calculations, variables contributing to issues, mitigation strategies and more. The theme of the presentation was “inflation,” and references to NFL quarterback Tom Brady—who was caught up in the much-publicized “Deflate-Gate” scandal earlier this year—were inevitably made.
“What happens when you fabricate an IG unit in Orlando … and you bring it up to Denver?” he said. “It gets inflated.”
A unit made at sea level is at 14.7 pounds per square inch (psi), he said, but 12.0 psi in Denver. At fabrication, pressure inside the unit equals pressure outside of the unit, and when altitude is changed, outside pressure is changed.
Haberer said the main issues that can result include glass breakage, IG seal stress that could lead to failure, interference with slider windows and aesthetics.
With glass deflection comes stress, and too much stress can equal breakage. “And it’s usually not a small break,” Haberer said. In terms of IG seal stress, deflection stretches the seal—with that, the cross-sectional seal area can increase and it can result in Polyisobutylene (PIB) voids. More moisture allowed in can result in early failure. Additionally, operation of slider windows and the way a window can look under these conditions is something the consumer and end-user could notice.
“Those are the four, so what’s going on?” Haberer asked rhetorically, noting it is “Boyle’s Law.” Boyle’s Law is a principle that the pressure of a gas varies inversely with its volume at a constant temperature.
Variables in the case of this effect on IGUs include glass area, aspect ratio, glass thickness and spacer width. Haberer showed attendees charts for the four variables and how they can be affected.
He then addressed mitigation strategies—tempering, fabrication at altitude, pressure relief tubes, capillary tubes, valves in the IG unit, etc.—and their respective challenges. Tempered glass, he said, is not a solution in all cases, as it only addresses glass breakage and not deflection. Fabrication at altitude, he added, isn’t a practical solution. With pressure relief tubes, argon can escape in transit, and pressure relief valves require a “critical” permanent seal. Pre-pressurizing units at fabrication requires precise filling and can cause stresses prior to a change in altitude. He also addressed ship-through concerns.
Ultimately, there is no one perfect solution, and the presentation sparked some dialogue among IGMA members as lunch concluded.
“It seems I accomplished what I wanted to out of this, which is to stir the pot a little bit and get us thinking and talking about it,” Haberer said as the session closed.
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