Low-E glass melting vinyl out 35′
NC is just getting hit with a rash of super weird problems with Low-E glass windows. Turns out the gas they are filled with causes the panes of glass to converge at the center and the low-e coating on the outer piece of glass acts as a heat mirror which causes infra red energy to concentrate at a place 35’ away from the glass esp. at sunset. It’s been melting stripes into vinyl siding on row houses in Durham and melted a line right through a solar swimming pool heater in Chapel Hill. Seems like the solution is either to positively pressurize the glass so it has a slight bulge in the center or else put the Low-E coating on the inner pane only.
It’s only a problem if you have a susceptible (ie low melting point plastic) target 35′ or so to the west of west facing glass. So it’s showing up in Energy-Star affordable housing where you have the convergence of low-E glazing and nearby homes with vinyl siding. Or in Chapel Hill where there was a third story low-E window that focused heat on the roof of the pool house where it melted the solar pool heater. Runs across at least two brands of windows.
NC is about to mandate low-e glazing in all new construction so we are expecting to see more of these kinds of failures esp in row houses. Anybody have any experience with this one?
Replies
While it obviuosly does happen, it really is a relatively rare phenomenon and is primarily associated with high reflectivity coatings.
Of course if it is your siding being melted then it doesn't matter that it is relatively rare!
I have a client that makes insulated glass units (the sandwich of 2 panes, spacer and gas. I can't recall the details, but they offer some customers (they sell to window makers) an equalizer tube that allows the argon between the panes to expand and contract as altitude changes. They lost one too many truckloads of windows being trucked across the Rockies.
While it depends a lot on the specific IGU type, glass size, and aspect ratio; it is ultimately up to the window manufacturer as to whether they want to risk a trip over the mountains.
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There are two primary styles of venting used in IGU/window manufacture.
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Typical “breather tubes” are aluminum, short in length, provide a relatively large opening for equalizing pressure, and they are “sealed” once the window has been installed. This is the type of venting unit that would be installed for a trip over the mountains. It allows the interior airspace of the IGU to breathe as pressure changes at different elevations.
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The “capillary tube”, on the other hand, is stainless steel, longer (~18”), has a very narrow opening, and it is never closed – it is left open to the air after the unit is installed.
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Although specific recommendations and usage are very much manufacturer dictated, as a general rule capillary tubes are used in dry, high altitude, environments to equalize pressure on windows actually installed in that environment. Again, they are not sealed when installed; they remain open to the air.
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At altitude the air is relatively dry and what moisture that does attempt to enter the IG airspace is limited by the design of the tube. The air exchange rate, when using capillary tubes, is much to low to be used simply to take the unit on a trip over the mountains.
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There are charts available that list the allowable stress of a window unit or IGU when crossing higher elevations. These charts include information on the specific IGU type, glass size, and aspect ratio and compare that with the altitude that the unit should be able to survive without damage to either the spacer system or the glass.
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When using either breather tubes or capillary tubes, the unit is not gas filled. The exchange of outside air with inside air makes filling the space with an inert gas a waste of effort and money. Whatever gas is put in there would be gone relatively quickly.
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And not all IG systems require venting to pass over the mountains. Some manufacturers do have systems that can survive a trip at elevation without damage. Although most manufacturers who wish to sell on both sides of the mountains have simply opened manufacturing plants on both sides of the mountains.
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I took many glass manufactures awhile to learn argon gas and glass sealents have a special relationship.
This is not a new problem, just one that has taken many years to show itself... fortunately for the manufacturers the problem is showing up near the end of their warrenties.
do you have a link to a news article about this? It sounds like something you'd see on Mythbusters.
No I gave a talk about green building and two guys in the audience had been having problems, one was the guy with the melted siding on several row houses on the same street with the same compass heading and distance from the neighbors and the other was a solar installer who replaced two panels before he convinced the homeowner to replace the offending window, that solved the problem. The guy with the solar panels said he managed to be on the roof in the late afternoon and witness the solar concentration, said he couldn't hold his hand in the hot spot and he was 35' from the window.
I've seen double-glazed windows crack on the inside pane due to ice on the outside pane concentrating the sun.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
sounds like the army's latest weapon
http://www.cnn.com/2007/TECH/01/24/ray.gun.ap/index.html
Maybe Andersen is conducting research for the DOD or Homeland Security.
Yeah, I was wondering about that. Supposedly the beam only penetrates about 1/64 of an inch. What would happen if you just wore wet clothes?
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
"What would happen if you just wore wet clothes?"
The report I heard on NPR said it wasn't affected by wet clothes or even wrapping with foil, although I could see that catching on in some quarters as a "fashion statement".
Mike HennessyPittsburgh, PA
The report I heard on NPR said that foil would probably work, though approaching a checkpoint dressed like a Trekkie would probably attract unwanted attention. Water wasn't mentioned.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Easiest way to foil the new weapon is to carry a lightweight shield made from foil-faced polyiso foam.
Yeah, but then they'll hit it with the low-E glass beam and melt it.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
a metal trash can lid works even better - already has a handle
"The report I heard on NPR said that foil would probably work, though approaching a checkpoint dressed like a Trekkie would probably attract unwanted attention. Water wasn't mentioned."
DOH! I was on my way out of the room when this was ending and I remember thinking "I wonder if foil would block it" when I heard mrmp, grbl FOIL, gbits.,. Guess I just heard wrong. It would make sense, though.
That raises the age-old question of . . . I wonder if this would fire off my SawStop?
Mike HennessyPittsburgh, PA
According to some folks at the members only ASHI forum, it's real, although some claim that it's just the low-e coating, the curvature doen't matter - others say the distance isn't fixed.
Ar=ttached is a pic someone posted (large and small file versions)
With my mouth I will give great thanks to the Lord; I will praise Him in the midst of the throng. For He stands at the right hand of the needy, to save them from those who would condemn them to death.
- Psalms 109:30-31
A reflective coating by itself couldn't produce any more heat than the direct sun.The focal length of the mirror created by a dual-pane window is going to be a function primarily of glass thickness and the amount of vacuum involved, with a less significant dependence on pane size, so the focal length will tend to be the same for a group of windows subjected to the same conditions. The pane will describe a shape pretty close to a parabola -- a perfect focusing mirror.It's probably unfortunate that high pressure and clear skys tend to go together. Add cool air temps, and you have a pretty good setup for creating this phenomenon -- the cool temps both increase the vacuum and make the "target" materials more susceptable to thermal stress damage.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
There have been several recalls of 'sun-room" units over the years; Four Seasons had a recall a year or two back for setting the surrounding wood-siding on fire.
About 20-30 years back there was a law-suit concerning double-pane units where the vent hole between the panes became plugged and created this situation.
Low-E or argon filled units can't be vented, but the glass is supposed to be thick enough to withstand the pressure changes They did make some location-specific units that didn't survive going to the wrong climate
Phill Giles
The Unionville Woodwright
And not all LowE coatings will melt siding. It has to be a highly reflective LowE coating and while LowE coatings are designed to be reflective, the majority of LowE coatings don't specifically reflect enough IR to cause such damage.
Regarding the 4-Seasons fire issue, the fix was simply to go with a less reflective coating in the roof of the sunrooms and to equalize pressure in the IG eliminating the concave glass and the concentration of heat on the siding.
Of course the fix also involved the replacement of some scorched siding!
Edited 10/16/2007 6:39 am ET by Oberon
I have the same issue. I am building a house next door to where I live now. Last Oct after installing the windows I started to notice that our front door and trim the paint was bubbling in 2" wide strips across the bottom. Over time as the angle of the sun changed the strips would move up the door. A couple of weeks ago I took a real close look at the bubbled paint and noticed it looked burned. Not five minutes later the sun came out and a bright sun spot appeared over on of the bubbles. After four months I now know what is causing the bubbling. I could not put my hand on the spot for more than five seconds. It also melted a garbage bag too.
I called Milguard today and they played dumb like they have never heard of this and said I could at my expense get a non low-e window which may help.
Jeremy
The guy with the melted solar panels got his window manufacturer to supply a new window for him but I beleive it was still low-E only with more argon in it or with the Low-E coating on the interior pane of glass.