Graham Wright is PHIUS’ Senior Scientist. He’s led the PHIUS technical committee in the development of PHIUS Certified Data Program for Window Performance. Here’s Graham to tell you all about it:
As you are aware, for passive house energy modeling, separate U-values are needed for the window frame and the center-of-glass (as opposed to standardized whole-window values) so that the building energy model can properly account for windows of different size and shape. In addition, it is sometimes very worthwhile to design thermally-broken window installation details, and to calculate the beneficial impact on the window installation thermal bridge coefficient. This requires some special support.Under our Certified Data program, the performance numbers for the window frames and the glazing are calculated by trained window simulators according to the published European passive house protocols.
In the process, care is taken to develop THERM models of the windows which are also suitable for use in calculating window installation thermal bridge coefficients. (Preferably these models are also published, in addition to the window performance numbers themselves, but they can remain private to the manufacturer and/or PHIUS.)
We’ve set no pass/fail criteria on U-values, only guidelines as to the thermal performance levels appropriate to various North American climate regions. Air-tightness looms as a larger concern and we are encouraging testing to ASTM 283, but this is optional for now.
In addition, there is a pilot program to harvest the detailed U-value information found in existing NFRC whole-window files, (which as it turns out, also account separately for frame, center-of-glass, and edge-of-glass heat loss,) and compare this apples-to-apples with the modified CEN values, with a view to possibly using NFRC data more directly in the future. In the meantime, NFRC certified THERM models can serve as time-saving starting points.
If you are a manufacturer who wishes to submit your product for the program, download a full description of the program and application. If you have questions, please use the comments section and I’ll monitor and respond.