A New Passivhaus Standard for North America
Katrin Klingenberg explains why the superinsulation standard developed for Central Europe is inappropriate for North America
Katrin Klingenberg, the founder of the Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Institute U.S. (PHIUS), caused a minor earthquake earlier this year when she suggested that the existing Passivhaus standard didn’t make sense in North America. On January 31, 2012, Klingenberg wrote, “We came to the conclusion that it’s time to allow for a modification process to the rigid annual heating and cooling requirement of less or equal to 15 kWh/m2yr … for the North American continent’s more extreme climates, and define what has been missing all together so far – a stringent requirement for the third load which is the significant energy consumed in North America for dehumidification. This idea that we need to adapt the standard to various regions has taken root around the world from domestic energy experts like Martin Holladay, Alex Wilson, and Marc Rosenbaum and to Passive House groups from other countries, like the Swedes.”
As GBA reported earlier this year, many U.S. Passivhaus consultants were unsettled by Klingenberg’s proposal. Their main concern: builders and home buyers would be confused by the existence of two different superinsulation standards that shared the same name. Because of this concern, Hayden Robinson, an architect and certified Passivhaus consultant based in Seattle, launched a petition urging Klingenberg to choose a name other than “Passivhaus standard” or “passive house standard” for her proposed new North American standard.
Klingenberg visits the Building Science Corporation
Joseph Lstiburek and Betsy Pettit, who host the annual Westford Symposium on Building Science in Westford, Massachusetts, invited Klingenberg to speak at this year’s conference. In her July 31 presentation, “Climate-Specific Passive Building Standards for the U.S.,” Klingenberg suggested several reasons why the European Passivhaus standard might need to be tweaked for use in North America.
She began by acknowledging a critic of some aspects of the Passivhaus standard: one of Lstiburek's partners, John Straube. “For 10 years, we have been strictly following the guidelines that came out of the German Passivhaus Institut,” she said. “When I defended these guidelines I was not exactly right but not exactly wrong. And when John Straube wrote his paper about the Passivhaus standard in cold climates, he was not exactly right and not exactly wrong. Now I propose a middle thing.”
How should Passivhaus address cooling loads?
Klingenberg did not beat around the bush. “The European standard may not be correct for North America,” she said.
Klingenberg noted that in a cold climate, it’s hard to deliver space heating through ventilation ducts. “A common definition of a Passivhaus is a house that can be comfortably heated only by preconditioning the ventilation air,” she said. “The Europeans came up with it because in Europe the peak load is the same as what can be transmitted by the ventilation system. But there is only a tiny region in the U.S. where that is possible. Everywhere else, the peak heating loadRate at which heat must be added to a space to maintain a desired temperature. See cooling load. is too high.”
In some climates, it’s possible for a home to be heated in winter just by internal heat loads like the refrigerator, television, computers, and lighting. However, the same approach won’t help cool your house during the summer. “The idea is to have a balance — to limit the heat loss so that it almost balances the internal loads,” said Klingenberg. “But what about cooling? How can I limit my peak cooling load based on passive principles?”
In hot climates, thick insulation is sometimes counterproductive. “One benefit of a Passivhaus is that when you raise the surface temperatures in a Passivhaus to make the house more comfortable, you will have no condensation or deterioration,” said Klingenberg. “If you pick a window with warm surfaces, there will be no condensation. But in summer, does that approach still work?”
Klingenberg did not have any suggested solutions to these quandaries. “We have some work to do,” she said. “If we consider cooling, it is infinitely more complicated. With the climate on the move, the entire U.S. will have a cooling problem.”
What about HVAC system savings?
Continuing her laundry list of problems with the existing Passivhaus standard, Klingenberg discussed the method that Passivhaus designers use to calculate a home’s area. “The reference area used for the Passivhaus standard — ‘treated floor area’ — is based on a rental rule in Germany, created to be fair to the renter,” said Klingenberg. “There is no building science there. Should we adopt it in North America? Or should we use the conditioned floor area that is usually used in the U.S.? If you use the area customarily used in the U.S., the energy metrics would look different.”
According to Klingenberg, the oft-heard European boast that it’s possible to achieve significant construction cost reductions by eliminating a conventional boiler or furnace doesn’t wash in North America. “In Europe, they have expensive hydronic heating systems,” said Klingenberg. “The initial argument is that there is a sweet spot that comes from eliminating the cost of a boiler. The idea is that if you consider total cost and savings, then Passivhaus is the most cost-effective path. That was the argument. But that is also climate-specific. In the U.S., forced-air systems are much more common than hydronic systems. Look at the BEopt curve.” (Klingenberg was referring to graphs developed by BEopt, a computer simulation program used to determine the least-cost path to zero-energy home design.) “It’s very different. You don’t see savings from eliminating an expensive hydronic heating system.”
She noted that many North American Passivhaus designers specify expensive HVAC equipment. “The giant drop in cost just doesn’t happen when you build a Passivhaus in North America,” she said. “Mostly Passivhaus adds cost, because we add expensive equipment from Europe. That might change if you could buy a ‘magic box’ built in North America for $3,500.” Unfortunately, such an inexpensive all-in-one appliance is not yet available.
Dehumidification is hard
To begin a discussion about dehumidifying homes in hot, humid climates, Klingenberg returned to the question of delivering space heat and space cooling through ventilation ductwork. “The European climate lends itself to a standard based on 1 Watt per square foot peak load,” said Klingenberg. “But the cooling case is way more complicated. What about dehumidification? This is where the whole thing falls apart in North America.”
According to Klingenberg, it makes sense to use ventilation ducts for space cooling and dehumidification. “Point-source dehumidification doesn’t work,” she said. “We learned that at the first Passivhaus in Louisiana.” But the European prejudice against recirculating indoor air through ventilation ducts limits North American designers — designers in very cold climates as well as designers in hot, humid climates — who can’t squeeze enough hot air or cool dry air through the low-airflow ducts promoted by the Passivhaus Institut in Germany.
It’s all in the hands of a committee
According to Klingenberg, she has no plans to be directly involved in proposing changes to the Passivhaus standard; those proposals will come from a committee. “PHIUS has set up a technical committee to look at these issues,” she said. “At the upcoming conference in Denver we are planning work groups to develop a climate-specific refinement of the Passivhaus standard. It is an evolutionary step.”
Klingenberg invited everyone in the Westford audience to provide suggestions for possible tweaks to the Passivhaus standard. Energy expert Marc Rosenbaum — who, as usual, spent all three days of the conference in his customary front-row seat — raised his hand. “Passivhaus should focus on source energy,” said Rosenbaum. “We need to limit peak loads. Get rid of 15 kWh per square meter per year. My advice is that you don’t focus on cost optimization, because the cost of energy varies all over the country, and that has nothing to do with climate. I’m urging you not to go too far down that road. Since the current standard is expressed in terms of square footage, it’s harder to do with a small building. A 5,000-square-foot Passivhaus is not a better house than a 1,200-square-foot ranch house built to meet the IECC International Energy Conservation Code.. What I am proposing is that the standard be shifted to a per-person target. If you look at the climate issues, they are ethical and moral issues about how much is enough. The last thing I’d like to say — and it’s tricky, Kat — is that we have to recognize how much the cost of renewable energy has come down. And we have to recognize that not every site has perfect solar access. Right now Passivhaus in a cold climate is impossible without good solar access. So what about buildings that don’t have good solar access?”
How hard is it to change the world?
After Klingenberg had shared her hope that the Passivhaus approach will eventually become standard practice in North America, Joe Lstiburek, a well-known building scientist as well as one of the conference hosts, stood up. “I’m going to have the last word on this,” said Lstiburek. “We have an incredible amount of natural gas coming online at a very low cost. If this proposal becomes a political program, it might work in France, but it won’t work in the U.S. We have cheap gas, low energy costs, and plentiful energy supplies, so this isn’t going to fly. If you want to change the world, this can’t become a boutique program like R2000 in Canada. The world around you is also changing — politics and the energy situation are both changing.”
Klingenberg did not appear deflated by Lstiburek’s remarks. Her only response: “I’m stubborn.”
Last week’s blog: “Do Foil-Faced Building Products Block Cell Phone Reception?”
- Martin Holladay
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