Replies

1. GBA Editor
   Martin Holladay | Oct 08, 2014 04:27pm | #1

   Paul,
   As far as I know, this issue hasn't changed. If you use this type of glazing, the interior pane will be at a cold temperature, increasing the chance of condensation.

2. 
   charlie_sullivan | Oct 08, 2014 05:46pm | #2

   It's a pretty fundamental issue--if a coating there works well, it will increase the effective U value between the window surface and the room. That means the that surface will be colder than it would be without the coating. The only thing you could change about the coating to reduce the problem would be to make the coating milder--make it do less. But then the benefit is reduced. U values for i81 and i89 are reported to be the same, so the condensation issue should be identical.

   Whether there is a condensation problem depends on indoor humidity, outdoor temperature, etc.

   Note that condensation on the center of the glass is probably better than condensation on a wood frame, where rot and mold are more likely.

3. 
   [email protected] | Oct 08, 2014 09:40pm | #3

   Good evening,

   This question has come up at least one time before:

   https://www.greenbuildingadvisor.com/community/forum/general-questions/27235/surface-4-low-e-condensation-issues

   Following is an significantly edited version of my reply to the question from the earlier post.

   Center-of-glass (CoG) is all glass area that isn't within 2 1/2" of the edge of the glass while edge-of-glass is that 2 1/2" bordering the sash.

   I81/I89 lower CoG about 9 degrees F compared with uncoated surface 4, but they only lower EoG about 3 degrees F, so the effect of the surface 4 coating is less in the area where window condensation is more likely to occur.

   Even with a 9° center-of-glass drop the glass will still be warmer when using a surface 2 and surface 4 coating combination than it would be if there was no coating used at all. In addition, despite the lower temperature of the glass, you will actually feel warmer when sitting in front of a window with a surface 4 coating that you would when sitting in front of a window without surface 4 coating.

   When using a surface 4 coating a low thermally conductive spacer system becomes even more critical than in a more conventional IGU where condensation is concerned.

   Most spacer systems other than aluminum are considered to be low thermal conductance and relatively few IGU's are being made with aluminum these days - probably less than 5% give or take a few.

   I89 is Cardinal's upgraded version of I81. U value improvement versus clear glass is about the same, but visible light transmission is improved to 89% using I89 versus 81% using I81.