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What's the difference between Passive House certifications?
We are a little biased, but we think for good reason. Only one certification is tailored to the climate that the building is in. We think that’s pretty important.
There are a lot of organizations with the words “passive house” in their title. Most of these are loose affiliate organizations, clubs, or groups of like-minded building professionals who want to design and build better buildings. They often want to combat climate change in their daily lives, and they recognize passive-house certification as the most stringent energy standard available. To smooth the learning curve, they form these support groups.
Despite the many “groups” and “networks” sporting the passive-house name, there are only two standard-certifying organizations: Passivhaus Institute (PHI), in Germany, and Passive House Institute US (PHIUS), in North America. Through most of their early existences, the passive-house standard was similar for both, and you could certify a building with either or both—depending on where the building was located or your personal preference.
Around 2012, that began to change, as PHIUS looked to improve the performance of buildings for North America’s many climate zones. We learned that designs for Germany’s climate don’t exactly work in Chicago, Houston, or Las Vegas. To improve building performance in hot, humid, cold, and mixed climates, PHIUS worked with Building Science Corporation (under a grant from the U.S. Department of Energy) to write the Climate Specific Passive Building Standard. This is an actual standard, available for jurisdictions to use as a model for building codes. We also worked with the Fraunhofer Institute of Building Physics to modify their WUFI hygrothermal modeling software into a design and verification tool for passive buildings tailored to tailored to North American climate zones and weather data.
The three-year study yielded a formula that we used to generate cost-optimized performance targets (annual heating demand, annual cooling demand, peak heating load, peak cooling load) for more than 1,000 North American locations. The results are remarkable: Early test cases show that observed energy use is extremely close to the expected energy use predicted by the model.
In the early days of passive house, there were fewer differences between PHIUS and PHI because we both used a spreadsheet to predict the energy use. The WUFI passive three-dimensional energy and moisture modeling software has created a large-enough gap in performance that PHIUS+ 2018 will no longer support the PHPP spreadsheet that is central to PHI certification.
PHIUS+ certification is the best, most efficient cost-effective, climate-specific path to a zero-energy building.