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IGU Filling: Why is Argon important to you and your windows?

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I almost wonder if the salesman was playing "your good old boy best buddy by offering a dirty little secret to let you know that he has only your best interests at heart and you really should buy from him since no one else is looking out for you like he is.... Wink "

Anyway, this is a bit of an older post of mine, but I think it applies in this case...there is a bit of extra data that wasn't part of the original question, but I have never been known to let that stop me Rolling Eyes

There are a couple of different ways to fill an IGU with argon. The vacuum method is not the most widely used and it is not cheap...the cost for development and equipment runs into the millions of one may ask why make that investment for something that is not reliable – for including a product that is going to fail? For something that can be done for much less money and for something that people may not even want because it may be a waste of money?

The cynical answer might be that it is possible to fool enough people into buying argon fill, even if it isn't worth it, in order to make a profit while paying off the high-tech process. But then there is the question, "why bother to invest in R&D and new equipment if quick profit is the only issue?" And if a company’s reputation rests on a product or process known by the company to be a failure?

There was a time when argon life-expectancy in an IGU was 5 to 7 years or possibly less. There was also a time when 8%-10% of all IGU seals failed in less than 10 years.

Unfortunately, for some manufacturers and manufacturing methods, those numbers haven't changed much, even today. But, for others, there have been significant improvement that is reflected in the products that they produce.

Argon leaks out of an IGU in two ways...slowly, over time by migrating thru the seal that joins the spacer to the glass in the IGU, or quickly, when that seal fails.

Most IGU's are constructed with desiccant between the lites to absorb excess moisture. This results in an internal (between the lites) dew point that is very low and helps keep the glass clear even in extremely low temperatures. This may also help to keep the IGU from fogging in the event of a seal failure.

If the seal fails, then the argon is replaced by air. For awhile (long while in a warm and dry environment) there is no evidence that the seal has failed. In fact, the overall performance of the unit (except for the argon loss) doesn't really change. The problem is when it gets cold enough to allow condensation within the IGU, then you will have fogging...or else, if the unit has a LowE coating, then that coating may begin to corrode when exposed to the air - if the desiccant becomes saturated and is no longer able to remove moisture from the environment.

But, beyond seal failure, there is also the argon's "ability" to migrate thru the seal itself; which does not result in air replacing the argon. The argon level has gone down, but nothing has replaced it.

Many materials have been used in an attempt to keep IGU's sealed both to keep argon in and outside air out. Since argon is a very small molecule, it migrates quite readily thru many materials; very few of the materials used in IGU spacer systems in the past could block argon migration for any length of time. Actually, keeping argon contained in an IGU for even 7 years or so was something of an accomplishment - but, obviously, it was not sufficient.

Without going into the history of seals and sealants, the best product currently in use to stop argon migration is polyisobutylene or PIB. PIB is a thermoplastic material and it is the only plastic currently known that is impermeable to gas - including argon. The TPS system is primarily PIB (85% if memory serves). Unfortunately, PIB is not a structural product, so it requires a second material to structurally bond the glass…specially developed silicones are used for this purpose as are hot-melt butyls and polysulfides. The PIB and silicone dual seal system is widely used among the largest window manufacturers in North America.

Another popular system uses foamed silicone as the primary spacer material (versus a metal spacer) and then wraps the silicone foam in a mylar film for gas impermeability since silicone alone will readily pass both moisture and argon. This system then uses a dual-seal that incorporates acrylic adhesive for its structural seal backed with a moisture vapor seal as well.

The point being that the primary manufacturers of both of these seal systems have spent huge amounts of money to develop testing equipment to check on both seal longevity and argon gas retention.

Additionally, outside corporations have also developed test devises for this purpose as well. These systems are now being used to track product performance both in laboratory and in field settings. The results in both settings indicate that argon loss is realistically estimated and measured at about 1% per year – in the top-of-the-line systems - seal failures have gone down to well below 1% over 20 years from as high as 8% - 10% over ten years – before the development of these new systems. In fact, the major IGU manufacturer in North America has reported that with their newest system seal failures are presently somewhat less than .1% over 20 years (one-tenth of one percent)…

The fear of losing argon from an IGU and the hesitancy of buying an argon-filled unit was valid a few years back – and still is with some systems even today, but the best systems on the market today have reached a point where avoiding seal failure and maintaining argon retention have become almost routine – something no longer a significant concern for the consumer.

Building Science for an example actually does recommend argon filled units, for their superior insulating capability, in several of their examples.

Posted: Fri Apr 14, 2006 7:24 am