I was wondering if anyone would be willing to share thermally broken
aluminum frame conductance values that they've been using in recent
Windows5 center-of-glass calculations. I don't have information on the
particular aluminum frames for my current project, so I don't really
want to try and learn THERM quite yet.

Most of the older documentation online that I've found shows that
thermally broken aluminum frames typically have a U-value of about 1.0.
This jives with one of DOE-2s window entries for a PPG glass with a
frame conductance of 0.94.

Almost every commercial building constructed these days is made with
aluminum framed windows...I just have a hard time believing that
manufacturers haven't figured out better ways to insulate the frames.
With vinyl and wood having U-values < 0.4, I have to think that aluminum
frames should be able to at least approach 0.5, if not lower.
Unfortunately not a lot of manufacturers of aluminum frames post their
thermal characteristics.

What are people using?

Thanks in advance!

James Hansen, PE, LEED AP