Gas Filling in 2012
What You Don’t See Is What You Get!
by Jim Plavecsky

Gas filling has really evolved over the years. Back in 1986 when the fenestration industry in North America was just starting out with the concept of inert gas fills, there was no quick way to tell how much argon was actually getting into IG units.

Guessing Game
Indeed, due to the fact that inert gas fills are invisible coupled with the fact that the industry had no easy way of detecting its actual presence in the IG unit, the perception that existed during the early years of gas filling was one of smoke and mirrors. Also, the belief at the time was that even if IG units were adequately filled with argon, no one could really guarantee if the gas would still be there a year later, let alone five, 10 or 20 years from the date of manufacture. There was also little concern about it leaking out. Many felt that if the argon did leak out, it would cause no harm as it is inert. The IG unit would still continue to function as normal and no harm would be bestowed upon the homeowner.

As the industry gained more experience with gas-filled units, we discovered that, over the course of time, argon permeates through polymer membranes at a rate faster than the air permeates into the unit to replace it. This is due to the Law of Partial Pressures. Each gas, whether it is argon, or the three major components of air: oxygen, nitrogen and carbon dioxide, behave independently and permeate at different rates through a membrane. Since argon moves from inside the unit to the outside faster than these other gases move inward, we have uneven gas exchange and the result is that a negative pressure is created within the unit. What effect does this have upon the health of the IG unit?

The negative pressure causes glass inflection, putting stress on the bond line and stretching the IG sealant. It also causes visible distortion as the IG unit becomes concave and behaves as a lens. The gap between the lites of glass is also narrowed, causing increased heat transfer and a rise in the effective U-value of the window unit.

No More Guessing
How we have changed in 20 years. We now recognize that gas leakage is unfair to the consumer, who purchased a window with an advertised U-value dependent to some degree on the presence of either argon or krypton gas. We also have a test regimen in place to evaluate and validate both the initial and long-term presence of gas within the IG unit. This could never have been possible without the development of quick and accurate measurement methods to determine gas fill rate levels in sealed units, both during the filling process and afterwards during the service life of the unit.

Initially, the National Fenestration Rating Council (NFRC) did not require any sort of testing to verify gas filling content or long-term retention but this has all changed. Now, manufacturers must submit test units to a certification lab, where they are evaluated for both initial fill rate as well as gas retention after weather cycling, which simulates many years in the field.

The NFRC has a plan in the works to take it one step further. It is launching an independent verification program, whereby window units will be purchased in the field and then tested to make sure they comply with the thermal testing as listed on the NFRC label. So the consumer will be assured that what he sees is what he gets. This analysis will of course also include a verification of the gas fill content of units purchased randomly in the marketplace.

One thing is for certain, because of these developments in measurement technology, combined with government funded industry regulatory programs, gas filling is no longer smoke and mirrors. What you don’t see is what you get.

Jim Plavecsky is owner of Windowtech Sales, a sales, service and consulting firm serving the door and window industry.

DWM
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