Gas Filling in 2012
What You Donít 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.
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
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 donít see is what
Jim Plavecsky is owner of Windowtech Sales, a sales,
service and consulting firm serving the door and window industry.
© Copyright 2012 Key Communications Inc. All rights reserved.
No reproduction of any type without expressed written permission.