Passive House Group to Certify Windows

October 29, 2012

At its September national conference, the Passive House Institute U.S. rolled out the first phase of a North American passive house window certification program. The initial goal is to calculate and make available valid thermal performance parameters for U.S. windows to provide designers with more choices and enable them to do building energy models with more confidence, officials state.

Energy modeling a passive house project using the Passive House Planning Package (PHPP) requires a particular set of performance numbers for each type of window used, the organization notes. National Fenestration Rating Council labels for windows list only a whole-window U-value and solar heat gain coefficient for a standard-sized window, while the passive house standard requires a more detailed set of specifications.

Such data was available for windows certified by the Passivhaus Institute in Europe. However, PHIUS officials note, these windows were all imported. As a result, the U.S. organization's technical committee began investigating how window performance values are determined using Window and Therm software developed by Lawrence Berkeley National Lab. The committee learned that much of the detailed data needed by passive house designers was already available. The group then proceeded cautiously with a pilot program of collecting crossover data from both NFRC and passive house protocols for comparison. 

PHIUS reports that four committee members are now signed up as window simulators in training, with the next steps including a peer review process that will eventually enable people to become fully qualified simulators. In addition to the certification program, officials say that eventually PHIUS will add quality and performance criteria to the window program. 

The organization is encouraging high-performance window manufacturers to participate in the certified data program for window performance, noting that doing so benefits manufacturers and their customers, and can aid passive house adoption in the United States and Canada. 

A full description of the program and application is available from the PHIUS website. Questions about the program can also be sent to Graham Wright, senior scientist and chair of the PHIUS technical committee at