The PHIUS Certified Data for Window Performance Program is here

Graham Wright

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:

Our PHIUS Certified Data Program for Window Performance is officially open for business!  (It was launched at the recent North American Passive House Conference in Denver.)
This program is mainly about using THERM and WINDOW software to calculate the window thermal performance numbers, which passive house consultants need to plug into their modeling software (either the soon-available WUFI Passive or PHPP).

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.

We’ve got several goals for this program. First, we want to serve our community of passive house consultants by providing PHPP-compatible window numbers. At the same time, we want to give U window manufacturers an alternative to European certification, and the opportunity to spend their certification dollars domestically.
The key differences between the programs are that:
1) We see a path forward to using NFRC protocols–in fact, the NFRC has responded positively about working together toward possible harmonization. Stay tuned.
2) The Euro certification maintains a pass/fail threshold tied to the Central European climate, while ours has guidelines instead, due to the wide range of North American climates.
Again, feel free to comment here at the blog.
Graham Wright

3 thoughts on “The PHIUS Certified Data for Window Performance Program is here

  1. Graham,

    This is absolutely fabulous! It will certainly help to bring clarity to the high-performing window market here in the U.S. and help it to advance more quickly. Thank you for heading this up and getting it done. Is the cost of window certification a flat fee per product? I’m going to spread the word. Thanks!


    • It’s not a flat fee but varies depending on the complexity. $150/hr, with a deposit required. The hardest cases will be those where there is no pre-existing THERM file and we need to create one from scratch from the drawings. NFRC-qualified THERM models, and .dxf files consisting of closed polylines, should help us economize. Also, just changing out different glazing systems with the same frame is faster than doing the frame in the first place (though not as much faster as in NFRC. They can be pretty much automate it in WINDOW but we have to do side calcs in Excel). The initial certification cost also covers the listing fee for the first two years.


      Graham Wright

  2. Pingback: More Windows Win Passive House Certification |

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