Saturday, February 2, 2008

Window Selection Update

Update regarding window selection Jan 26, 2008

After gathering additional research regarding using Alpen glazing and Mueller windows we have discovered that Alpen indeed has made tremendous progress regarding improving window performance, however it appears that the glazing is the reason they get the performance results they are claiming and the frames do not compare with the Mueller window regarding performance.

The National Fenestration Rating Council (NFRC) is the label to tell you the energy performance values for the entire window system. All the values on the NFRC label represent the rating of the windows/doors as whole systems (glazing & frame).

· The NFRC rating for the highest performing Alpen windows, (north facing cold climate window) as mentioned in an earlier discussion has a U factor of between .10 and .14 depending if it is fixed or an operable window.
· The equivalent rating for the Mueller window is .15 (This is using the Mueller 3-wood frame window assembly with standard European glass, not heat mirror glass as in the Alpen window).

It became apparent that the real benefit of using Alpen was for their high quality glass. The center of glass .10 goes along way in helping the overall unit perform as well they do. So we asked Klaus to check on his ability to get an equivalent glass product and we asked Alpen to send us the best they can do for glass they would supply to have installed in the Mueller window frames. Here is what we discovered:

o Alpen glass (Alpen performance glazing, Inner/Outer PPG 3/16”, Starphire Low Iron Glass/Double Heat Mirror, Suspended Coated Film filled with Kryptonite):
South facing
· .11 U value
· .53 Solar Heat Gain Coe
· 1 ½ inch
North, West & East Facing
.08 U value
.44 SHGC

o Mueller glass (Similar Heat Mirror and glass assembly)
South facing
.088 U value
· .52 SHGC
North, West & East Facing
.07 U value
.37 SHGC

With some adjustments to the window operation and design we think that the better overall option will be to use the Mueller window with the European glass options
described above, the overall NFRC will likely be in the .1 U value range, especially if we improved framing details as shown in the attached drawings.

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