Hi Dan

You should get your PSI Value from your window manufacturer. The PHPP uses the Value used with the German way of calculating it. The window size is 1.23m x 1.48m. the PSI value of the Frame stays the same but the U-Value changes with the size of the window

I hope it helps

Regards

Thomas Froehlich

Ryan at PHIUS told me to just pick a defensible number for the window install Psi value. But I wonder how PHI in Germany would explain their spreadsheet?

I decided to apply an uninsulated sill value from the Passive House Details Book uniformly to head, jambs, and sill; since in my case the window frame is not insulated from the exterior. If I had insulated from the exterior on head and jambs, I'd apply a weighted average value that includes the uninsulated sill. I'd use the most horizontally-proportioned window for my average, being conservative.

Using Moffett Field (Mountain View, CA) climate data, I'm not getting much difference either way. My guesses at "Shading" and wind protection coefficients make much more difference in my bottom line.

If I were developing a PH standard for California, I'd do tedious calculations for shading factors and guess at thermal bridges, rather than vice versa. Dan Johnson Arkin-Tilt Architects