PHIUS+ 2015 Climate-Specific Passive Building Standard
What's Changed, What Hasn't
In March, Passive House Institute US (PHIUS) implemented a new climate-sensitive passive building performance standard. PHIUS+ 2015 gives designers and builders a simplified, cost-effective path to resilient, comfortable, net zero energy buildings.
The new metric generated healthy discussion in the existing PH community and has brought welcome excitement and fresh interest from newcomers. But there has also been misunderstanding and confusion.
It’s important to understand what’s changed, and what hasn’t.
PHIUS+ 2015 is a natural evolution for PH. It is not unprecedented. Switzerland, Sweden, and Belgium are among the nations that have adapted PH to their conditions.
The fundamental PH goals and principles are universal and unchanged:
- PH drastically reduces energy consumption and carbon emission by reducing heating and cooling loads.
- PH employs a systems-based, whole-building design approach.
- PH is a performance standard (not a prescriptive checklist) with metrics that can be modeled and verified.
The design principles also remain unchanged:
- A PH is superinsulated.
- The building envelope is extremely airtight.
- Windows and doors are all high-performance.
- There is some form of balanced heat- and moisture-recovery ventilation and the smallest possible space-conditioning system.
- Solar gain is maximized for heating and minimized for cooling.
Then & now
In the 1980s, two European scientists—Bo Adamson and Wolfgang Feist—refined the application of PH principles. (Feist went on to found the Passivhaus Institut in Germany.)
Feist’s work yielded a performance metric that marked the point where, in Europe, minimizing mechanical systems offset increased costs for the building envelope.
That metric was thought to be universal. The performance target (4.75 Kwh/ft2 annual heating load) would apply in Germany, San Francisco, Boston… It was a powerfully seductive idea: One world, one metric.
Fast-forward to today. PHIUS has certified and/or consulted on residential and commercial PH projects across North America and concluded: One size does not fit all.
In some cases, the European metric has led designers to make decisions that cause overheating. In others, they had to install prohibitively expensive levels of insulation. And cooling climates present a whole different set of challenges.
Market conditions can vary as widely as climate conditions. While the principles have proven to be universal, the performance metric has not. It served to get designers and manufacturers to push the envelope. But its limitations were confining PH to a niche.
That’s why PHIUS, in partnership with DOE and the Building Science Corporation, set out to optimize the target metrics for North America.
Three years of research modeled buildings across the continent, employing BEopt (see “Using BEopt to Optimize Home Energy Performance” on p. 24) and WUFI Passive, a PH modeling tool.
The work yielded a formula: Climate and other variables are input to generate efficiency targets that are aggressive, climate-specific, and cost-effective.
Download the full report, Wright, G., and K. Klingenberg. Climate-specific Passive Building Standards, BA-1405, Building America, March 2015.
Learn more about PHIUS+ 2015.
Still Passive House
It’s important to note that the PHIUS+ 2015 metric is an optimization of the European metric, not a relaxation. In fact, in some climate zones, PHIUS+ 2015 sets the bar higher, because until now, cost-effective energy savings were being left on the table.
To account for changing market conditions, available materials, and climate change, PHIUS will update the standard on a rolling cycle.
But passive house is passive house—the concept and principles remain the same.
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