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Feistís Physics

January 2011

Interview by Jane Kolleeny

Dr. Wolfgang Feist has studied and researched the physics of buildings since 1973 at universities across Germany. He founded the Passivhaus Institut (PHI) in 1996 and is currently the acting director of PHI, and a professor of building physics at Innsbruck University in Austria. In January 2008, Passive House U.S. was authorized by PHI as the official certifier of Passive Houses in the U.S.

Dr. Wolfgang Feist is the founder and director of the Passive House Institute in Germany.
Illustration by Jorge Colombo

Dr. Wolfgang Feist is the founder and director of the Passive House Institute in Germany.

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GreenSource: How does Passive House (PH) compare to other benchmarks of sustainability?

Dr. Feist: To be honest, I don’t know exactly what the other definitions are. We are not trying to compete with anybody. PH is just showing a concept: how to design a state-of-the-art, energy-efficient building. It’s focused on performance—measuring heating, cooling, and dehumidification requirements.

GS: Does PH limit itself to the building envelope?

Dr. Feist: The general principle is to see what you need for comfortable indoor air quality and climate. Then ask how to provide these services with as uncomplicated a system as possible. It’s a good idea to look to the envelope, because all the heating and cooling issues have to do with creating a separate indoor and outdoor climate. So there is a concentration on the envelope, but its not limited by it.

GS: Are small windows necessary for certification?

Dr. Feist: We don’t have criteria for the size of windows; PH is a performance standard. If you have a large window, you’ll have to design for a reduction of the solar load in the summer. Some designers decide not to have such big windows, because they’re more expensive.

GS: How does PH address air quality?

Dr. Feist: By having such a tight envelope, you need efficient ventilation to meet air-quality requirements. This is done with a mechanical system that provides the inhabitants with ongoing fresh air. Using mechanical ventilation with heat recovery, indoor air pollutants are actually at lower levels in a PH.

GS: How do you determine PH certification?

Dr. Feist: There are things you can calculate, like the R-values/thermal bridge effects, and we have put it all in a spreadsheet calculation. Of course there are some issues like shading and air tightness that you can’t calculate. A simple blower door test measures how much air-flow you have and proves the air tightness. You will not be able to make the building completely tight; that’s not the goal—it’s not a spacecraft or an aircraft.

GS: Is PH viable in larger buildings?

Dr. Feist: Yes, the standard applies to all passive buildings. In Europe we already have lots of larger PH buildings. There is almost no limit to what you can build to PH standards.

GS: Why hasn’t PH caught on in the U.S.?

Dr. Feist: While there are only a few high efficiency components available in the U.S. so far, one of the next steps is to motivate American manufacturers to produce them and encourage small and medium businesses to specialize in these offerings. A discussion is currently underway with USGBC to have Passive House included in the LEED certification process.


This article appeared in the January 2011 print issue of GreenSource Magazine.

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