US Updates Passive House Standards

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Monday, March 30th, 2015
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The Passive House Institute US (PHIUS) has updated its building energy-efficiency standard with climate-specific data.

The organization partnered with the Building Science Corporation, and funding from a US Department of Energy grant, conducted research and generated data for more than 1000 locations in North America.

According to PHIUS, the new metrics “represent the ‘sweet spot’ where aggressive carbon and energy reduction overlap with cost-effectiveness.”

PHIUS director of communications Michael P. Knezovich noted that the new metrics would make the Passive House standards more efficient.

“Over time we’ve discovered that a single metric is totally unworkable in some climates, and in others, drives designers to make some iffy decisions in the interest of hitting the number (overglazing on the south,)” he said.

The previous standard included three metrics required of all projects, no matter where located. Developed by the Passive House Institute in Germany, those requirements applied to annual heating and cooling demand, total energy use, and air tightness.

According to Knezovich, one standard for all projects “just doesn’t work in the real world,” a conclusion also reached by Swedish and Swiss Passive House designers.

“Why would anyone think a single metric would work for Minnesota and Brisbane?” Knezovich said. “Costs are different, and materials costs change. At one time, adding insulation compared more favorably with the costs of photovoltaics than it does now. Things change.”

The updated Passive House standard, in contrast, lets users input city, state, location of climate station, and ASHRAE Climate Zone. The program then provides metrics for that location regarding:

  • Annual heating demand
  • Annual cooling demand
  • Peak heating load
  • Peak cooling load
  • Manual J peak heating load
  • Manual J Peak Cooling Load

Changes in the new standard are as follows:

  • The air-tightness standard has been changed from the previous limit of 0.6 ACH50 to 0.05 CFM50 and 0.08 CFM75 per square foot of gross envelope area. The change allows the standard to scale appropriately based on building size. The researchers determined that moisture risk is correlated with the leakage rate per unit area of surface rather than volume.
  • Economic feasibility drove the changes to the space-conditioning standard. The new standard requires climate-specific thresholds on specific annual heating and cooling demands and peak heating and cooling loads. This change helps to ensure that “efficiency measures will have reasonable payback relative to operational energy savings.”
  • The source energy limit saw many changes, including a change to a per-person limit rather than square feet of floor area. Another change makes the Passive House standard friendlier to on-site photovoltaic systems.

Also new in the 2015 standard are three optimising steps to net zero source, as stated at the PHIUS web site (http://www.phius.org/phius-2015-new-passive-building-standard-summary):

  • The designer focuses first on reducing heating and cooling energy use by passive means (envelope improvement and including some mechanical devices) and is guided in doing so cost-competitively by meeting the pass/fail energy metrics set by climate as presented in this report.
  • The next priority entails reducing total energy demand by efficient equipment (and some renewables), guided in doing so by meeting the source energy criterion which assures meeting the fair share global carbon limit,
  • Finally, there is the prospect of achieving zero source by more renewable generation. This can be done at construction or, consistent with the 2030 Challenge, by 2030.

Though nascent in Australia, Passive Houses are starting to gain attention. Currently, six Certified Passive Houses are listed in the Passive House Database. The Australia Passive House Association was formed as a nonprofit group to promote the standard and provide resources such as conferences and education. Several builders advertise their services in building Passive Houses, and a few designers have become certified.

Though not yet at the forefront in residential green building, Australia is the world leader in commercial green building, according to the latest Global Real Estate Sustainability Benchmark (GRESB).

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