The original standards made sense in the relatively consistent maritime climate of north-central Europe, says Katrin Klingenberg, executive director of PHIUS. “But in the context of the extreme climates of the U.S., designers were sometimes forced to choose strategies that had unintended consequences,” such as overheating from too much glazing, she explains. The new standards also represent PHIUS's further divergence from the criteria set by its parent organization, the Passivhaus Institute (PHI) in Darmstadt, Germany. The two broke contractual ties in 2011.
The original Passive House standards, devised to minimize energy loads, were balanced on just three pillars: a space-conditioning limit of 4.75 Btu's per square foot per year; a source energy cap (usually the total electrical demand) of 38,000 Btu's per square foot per year; and an airtight envelope criterion of no more than 0.6 air changes per hour at 50 Pascals of pressure. The revamped standards maintain these three pillars, but expand them.
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