Spacing: What does it affect?

Source Post: http://www.replacement-windows.com/windowbb/viewtopic.php?t=456

Post subject: Great thread!

Good thread, I really have enjoyed it. Like Guy said, debating the perceived pluses and minuses of the windows makes a heck of a lot more sense than trashing the person who gave their honest opinion.

A few comments on IGU space width.

Optimum spacer width is dependent on whether or not the IGU has a LowE coating and a gas fill.

For example, a dual pane IGU with a softcoat LowE and argon gas reaches its optimum energy perfomance at 7/16". Beyond that spacing, up to about 7/8", the energy perfomance will be pretty much consistent, but it does not improve. Above 7/8" the performance actually begins to decline. This is not a sudden "fall off a cliff" sort of degeneration, but is measureable.

If the IGU has a LowE coating but not an argon fill, then the optimum space is closer to 1/2" to 9/16". Again, the width increase up to about 7/8" has pretty consistent energy performance, but beyond that width it begins to decline.

Guy made an excellent point about STC. The wider the width of the airspace, the better the STC performance. Unfortunately, a good spacing for energy is not a good spacing for sound attenuation and visa versa.

If someone might be considering a narrower spacing in an IGU (a triple pane application for example), then using krypton gas infill becomes very significant.

An IGU with krypton gas fill reaches its optimum energy perfomance numbers at about 7/32"...and ideal spacing for a triple pane window.

At 7/32", argon and plain old room air have almost identical numbers.

Krypton performance does begin to drop off as the width increases, but even at 7/16", argon's best "spot", an IGU with krypton fill is still a bit better than argon...but not nearly enough to justify the additional cost of krypton.

JScott, I am surprised that you have had problems with Eagle and getting parts. The company has gone thru a couple of ownership changes, but the basic "organization" really hasn't changed at all.

When windows are tested for a DP rating, they are actually subjected to a force (in PSF) that is 1-1/2 times the DP requirement. For example, a DP rating of 50psf is actually tested at 75psf...a DP of 40 is actually tested at 60psf.

Wind velocity versus DP (psf) is not an exact correlation because winds have a way of swirling and changing, but 40psf equates to a windspeed of

127mph and 50psf equates to 141mph. There is certainly a difference there, but I am guessing that if you are subject to winds over 120mph, you are not worrying about the finer points of the 14mph difference.

And, don't forget that the DP40 is tested at 60psf which is about a 144mph and DP50 is tested at 75psf which is a windspeed of 173mph.

If you want to see serious DP numbers, check out a few of the impact / hurricane products available. Some of the companies mentioned here have DP ratings of 90+ on specific impact products.

McDonald's coffee is no longer served "too hot". After the lawsuit they dropped the serving temp of their coffee to about 130 degrees (like everyone else). Prior to the lawsuit they served it at about 190 degrees....a bit of trivia! Wink

Source Post: Marvin Ultimate, Marvin Invinity, Loewen, or Kolbe?
http://www.replacement-windows.com/windowbb/viewtopic.php?t=456

Posted: Tue Mar 15, 2005 11:07 pm