A Conversation With Wolfgang Feist
Questions and answers about the Passivhaus standard
Dr. Wolfgang Feist, the physicist and founder of the Passivhaus Institut in Darmstadt, Germany, began his U.S. speaking tour with a presentation and panel discussion at the Boston Architectural College on October 23, 2010. Among the other speakers at the event were 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. in Urbana, Illinois.
After suffering some public relations stumbles in the past, Feist and Klingenberg have polished their presentations. In Boston, they steered clear of the awkward exaggerations and red herrings that have marred previous U.S. discussions of the Passivhaus standard.
When I first interviewed Dr. Feist in December 2007, he explained, “As long as you build a house in a way that you can use the heat-recovery ventilation(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. system — a system that you need anyway for indoor air requirements — to provide the heat and cooling, it can be considered a Passivhaus.” Since this method of heat delivery has proven to be extremely difficult in the cold climates of North America, many American designers were confused by Dr. Feist’s insistence on it. Refreshingly, Dr. Feist made no mention of this method of heat delivery in his Boston presentation.
In marked contrast to claims made at the 2009 Passive House conference in Urbana, Illinois, where the keynote speaker, Günter Lang of Austria, falsely claimed that Passivhaus buildings don’t require a heating or cooling system, Dr. Feist was forthright and candid during his stay in Boston. “In the heating climates, a Passivhaus building is not a zero-energy building — you still need to heat it,” Dr. Feist told his American audience. He later explained that, if you are building in a hot, humid climate, “You will need a small cooling system or a small dehumidification system.”
The five elements of a Passivhaus building
In his presentation to the Boston audience, Dr. Feist boiled down the Passivhaus approach to five elements:
● High levels of insulation
● Reduction of thermal bridges
● Attention to airtightness
● The use of “energy-gain” windows
● Heat-recovery ventilation
This “return to the roots” approach was well received by the American audience.
A tip of the hat to superinsulation’s North American roots
Katrin Klingenberg's presentation included a welcome review of the history of superinsulated houses. She shared slides showing many recently completed Passivhaus buildings, including the Smith house in Urbana, the Waldsee BioHaus, the Passivhaus residence on Martha's Vineyard, the 2007 and 2009 Solar Decathlon winners, the Isabella Lake house, Rachel Wagner's "almost" Passivhaus, Tim Eian's House in the Woods, the Whistler Passivhaus, the retrofit in Sonoma, California, the GoLogic project in Belfast, Maine, the Bilyeu Homes project in Salem, Oregon, and the Studio 804 house in Kansas City.
Klingenberg also announced the upcoming Passive House conference to be held in Portland, Oregon on November 4 -7, 2010.
Upcoming challenges for Passivhaus proponents
I had two opportunities to interview Dr. Feist in Boston. The first occurred before the symposium began, when about 20 people gathered in a lounge at Boston Architectural College for an informal get-together.
Later, during a mid-afternoon break, I was able to ask Dr. Feist some follow-up questions. Unfortunately, there wasn’t enough time to ask Dr. Feist all of the questions suggested by GBAGreenBuildingAdvisor.com readers. However, GBA’s podcaster Chris Briley was able to snag an evening interview with Dr. Feist; Briley’s report of his interview will soon be posted on GBA.
I found Dr. Feist to be warm and eager to answer questions from American architects and journalists. The Passivhaus standard is gaining traction in the U.S., and that’s good news. Several challenges to more widespread adoption of the standard still remain, however. It seems to me that U.S. Passivhaus proponents need to focus on:
- A correction of the small-house penalty inherent in the standard;
- Better advice for those building in very hot or very cold climates;
- Better answers to questions about cost-effectiveness — especially, questions about the cost-effectiveness of measures necessary to achieve a maximum annual heating energy use of 15 kWh per square meter.
Dr. Feist began by introducing himself to the people gathered in a lounge area.
Dr. Feist: I was born in Germany. I worked in physics until the early ’80s, and then worked on energy-efficient buildings.
My work was inspired by people like William Shurcliff, who has written books on energy-efficient construction. There were important papers from the late ’70s and early ’80s, when guys were working on superinsulation. We always considered this information in Europe. There were a few research groups in U.S. and Canada, a few in Europe. These researchers were in contact with each other. But at the beginning of the ’80s, there were almost no low-energy buildings in central Europe.
"...It turns out that it is like learning to ride a bicycle: When you first see it, you don’t believe it is possible, but afterward, you see that it is easy."
Then there was a research meeting in Sweden in Lund University. Bo Adamson, the professor acting as a ‘secretary of foreign affairs,’ had studied developments in low-energy construction in Vietnam and China. He came back in the middle of the ’80s from China. He wanted to build passive houses. He told me about that, and I thought, ‘Oh, he has gone crazy.’ He had seen some passive house developments in southern China.
These things got started. We did research on the early development. There was research in U.S. and Scandinavia. We designed the first project in Darmstadt, and that turned out to be successful.
Since that time we are working on dissemination. There has been a lot of development since the mid ’90s in this field. There are now initiatives in all the European countries, including Russia and Belarus, in the Baltic countries, and almost all countries on the European continent. Already Passivhaus represents 10 or 12 percent of all new construction in Austria and Germany. We have had a big influence on the development of the building sector.
The first reaction you get from building professionals is, ‘That’s impossible. That won’t work. It’s too tight. Can’t we do it less tight?’ But we insisted in these tough figures, and it turns out that it is like learning to ride a bicycle: When you first see it, you don’t believe it is possible, but afterwards, you see that it is easy. That’s how it always worked in all these countries.
At the moment, I am in two places: working as the scientific head of the Passivhaus Intitut in Darmstadt, and also working at Innsbruck University.
Are climate-specific standards in the offing?
MH: Is there any discussion now about developing climate-specific standards for very cold climates or very hot climates?
Dr. Feist: There are already some examples in really cold climates. But the conditions are grounded in a real performance standard, so this is always a tough thing to change. So at the moment we don’t think much about changing the standard.
[In different locations] there are different boundary conditions. We have to look at these conditions, and we also have to adapt the [building] components and some of our recommendations. One of the major developments is, the next Passivhaus conference [in 2011 in Austria] will be about these regional developments.
Homes without air conditioning have low energy bills
MH: In hot climates, do you think it’s necessary for the occupants of Passivhaus buildings to accept high indoor temperatures in order to achieve energy use targets? After all, you can save energy by having no air conditioning.
Dr. Feist: There is a lot of discussion about that. To be honest, I don’t believe in that [the need for high indoor temperatures]. As long as people have a choice, [they will want] to choose comfort. In that situation we won’t be able to change that.
In the heating climates, a Passivhaus building is not a zero-energy building — you still need to heat it. The same is true for hot climates and humid climates. You will need a small cooling system or a small dehumidification system. So then we should stick to the goal of providing the best possible comfort — not by avoiding the use of cooling, but by reducing the cooling load to a very low level. Depending on the climate, you may need dehumidification, and it is very important to have shading. [We are looking at] the field of humidity recovery in the humid climates.
European windows and HRVs are expensive
MH: Some U.S. builders question the need for European equipment — for example, European triple-glazed windows or European HRVs — because they are so expensive. It’s hard to justify the high incremental cost of European equipment compared to North American equipment. The energy saving achieved by upgrading to European equipment is relatively low, especially considering to the high incremental cost of these components.
Dr. Feist: The Passivhaus standard doesn’t insist of using special types of components. It’s a total performance standard. You can use any component you want to use, as long as you can achieve the performance goal.
My recommendation is not to use the imported components. You don’t need state-of-the-art components. My recommendation is not to import windows from Europe, but to foster the development of really efficient American types of equipment.
This is what happened in Europe. We have had the exact same discussion in Europe. At the beginning, the only available HRV was a Danish one, and in Germany we didn’t want to buy a Danish one. But we were able to help small enterprises in Germany, and in the end the HRVs they produced were even better than the ones from Denmark.
It’s a very interesting thing to develop these heat-recovery systems. You will need a lot of different types in different climates. In some climates you need ones with humidity recovery; all of these are different systems. It’s not so difficult to do that.
It’s a chance for small and medium-sized enterprises to get into that [manufacturing equipment]. It wouldn’t take that long [for U.S. companies] to make joint ventures with the companies that have done this work in Europe. They are small and medium-sized enterprises. This is one of the effects of the Passivhaus performance standard, it makes a point for doing that [equipment] development. This is opening the door for small and medium-sized enterprises, opening the door to better construction standards, opening the door for more architectural freedom. This is very important.
"It might not be possible to renovate all buildings to the Passivhaus standard. Some [buildings] you don’t want to change, for several reasons."
In an existing building, it’s tough to achieve the standard
Chris Briley: Does that same philosophy hold true for renovation? Right now, it is very difficult to renovate and meet the Passivhaus standard, and we hear a lot of blowback. Many people say there ought to be a renovation standard with a different airtightness threshold — instead of saying, ‘This is the line in the sand. This is the brass ring.’
Dr. Feist: With existing buildings, the philosophy is a little bit different. It might not be possible to renovate them all to the Passivhaus standard. Some [buildings] you don’t want to change, for several reasons.
It is very important to get better components — for example, windows with really good triple glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill.. When it comes to cost, in Europe, they also said, ‘It’s too expensive.’ But the cost of these windows has dropped by a factor of three. Now the philosophy is, you can use these components in retrofit. Once these components are available, that will define how far you can go with the existing stock of buildings.
It is not a good idea to have a different Passivhaus standard for retrofit of existing buildings, because it might be too tough — then there will be complaints — or it might not be tough enough, so it is too easy to reach, and maybe you could do more in most of the buildings.
I think you should do what you can on a reasonable level. We were surprised in Europe to learn that a thing like the airtightness standard was possible in all the projects we have done so far. They all came under 1 ACH at 50 pascals. If you are that tight, of course you need a ventilation system.
Insulation is a different thing. With some buildings you can do external insulation. But there are lots of buildings where you cannot do external insulation. And internal insulation is much more difficult. You will never reach the Passivhaus standard with internal insulation, because of thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. .
In Europe, the surprising result so far is that almost always we were able to reduce the overall energy consumption for heating and air conditioning by a factor of three or four. All of that information is published. If you want to get that information, that is all available on the Internet. There are some Internet pages that you can log onto. One is the Passive House International site.
Questions from the crowd
Q. from the crowd: Is that information only available in German?
Dr. Feist: We need to bring this information to a Wikipedia-type structure. We just started the ‘Passipedia.’ The site is already in a state where we can gain lots of information from people’s experiences. With all of these old publications, it’s true that most of them are in German, but I hope some will be translated.
Q. from the crowd: With these retrofit projects, what percentage of energy savings are due to airtightness changes?
Dr. Feist: In an old building, the highest part of the losses are due to bad insulation — to conductionMovement of heat through a material as kinetic energy is transferred from molecule to molecule; the handle of an iron skillet on the stove gets hot due to heat conduction. R-value is a measure of resistance to conductive heat flow. and radiation. If you start with an old building, the first step is always insulation. Then the next step is airtightness. [Editor's note: Dr. Feist later clarified this statement with the following comment: “The ‘first’ was never meant to be a timeline order.” Further discussion on this point can be found in the posted comments below.]
If you have air flow through the structure, humid air flowing through the construction, you can get condensation. That is the most important reason it has to be airtight, to avoid problems due to structural damage from moisture.
The structural damage problem is the reason why the airtightness requirement is a separate number. That was one of the experiences in very early superinsulated houses — there were often problems, structural problems, from condensation. [Dr. Feist turns to me and asks me for confirmation. I agree.]
"These airtightness details are all a question of design. It’s not a question of the quality of work on the site; it is a question of design."
Condensation and rot can occur in an airtight building
MH: But it is still possible to have condensation problems in a building that is perfectly airtight. That’s what happened in Juneau, Alaska. Convective loops brought warm, humid air in contact with cold sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , and there was rot — even when there was no exfiltrationAirflow outward through a wall or building envelope; the opposite of infiltration..
Dr. Feist: It is always a good idea to have it as airtight as possible. From a technical point of view, having a figure of .6 ACH or its equivalent in metric units will give you a good guarantee that you don’t have damage from infiltration or exfiltration. Of course the design has to be reasonable. You could have others sources of humidity, and you have to keep that humidity out of the construction as well. But concerning this part of the problem — the problems that come from infiltration and exfiltration — you can get rid of those problems if you get it really tight.
About whether to change to practices that are less airtight — lots of people think the standard is difficult to reach. But I think it isn’t. We always have that discussion. We had that discussion in Czechoslovakia. People said, ‘It’s impossible.’ But when we made some education, it became possible. We said, you might have problems at first, but then it turns out to be really easy.
The airtightness level we normally reach after building three or four houses is .2 or .4 ach50. That’s what we normally come to.
These airtightness details are all a question of design. It’s not a question of the quality of work on the site; it is a question of design. The designer must know what is the airtight layer, and how are the different parts of the structure all connected. It is not the handcraft person who achieves that — it is the designer who does that. It is quite easy to reach.
More questions from the crowd
Q. from the crowd: How do these buildings hold up over the years?
Dr. Feist: We have experience going back more than thirty years. The Saskatchewan house is still in use. It is still like it was in the very beginning. It worked really well. There are other examples from Germany that are 15 to 25 years old.
What is important is to have the philosophy — to think about how to guaranty airtightness for the lifetime of the structure, and not just the for the pressurization test. It is necessary to have those details in the design, to have that in your construction plans.
Q. from the crowd: What about best practices for vapor barriers?
Dr. Feist: We are talking now about airtightness. There is no requirement for this to be a vapor barrier. It could be but it doesn’t have to be.
The vapor barrier discussion is much more complicated. It differs depending on the climate. Nowadays we try to avoid vapor barriers. Not that vapor barriers are a big problem — a vapor barrier can work if it is done the right way. But much more important than the vapor barrier is the air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both..
If the vapor barrier is not airtight you really run into problems. So the latest developments in Europe go in the direction of avoiding a vapor barrier, but having a vapor retarder on the warm side of the structure, to allow it to dry out if there is any moisture.
Q. from the crowd: Where can I get more information?
Dr. Feist: Passipedia.org has a part that is open to the public, to help answer the frequent questions, such as, ‘Can we open a window?’ — it seems we always have this discussion. Then there is another level [of the Web site] only open to members of the Passivhaus associations worldwide.
The idea is to share solutions, so you don’t have to reinvent all these things over and over again. That’s the concept of the Passipedia, so you can get ideas from countries with different climatic conditions, you can see some clever solutions they have invented in Korea that could be useful at your place as well.
We will provide a thorough scientific check of the information as well, because there is a lot of nonsense everywhere, a lot of these myths about damage from very tight construction, and bad advice — for example, that you are not allowed to use wooden construction. So we will check the information all the time from a scientific point of view. Sometimes information changes, because we reach a new state of knowledge. It’s important to know that. We try to follow this scientific approach. I think this is very important to follow the process of science.
It’s important to remember that there are more built passive houses than certified passive houses. Certification is important, especially for the first project. For the first project you need that quality assurance. The only way to prove a concept is to check it. But now in Europe there are architects who are building their 150th passive house, and they don’t certify every building. So certification is not at the center of our work. The center is the outlook, not the certification.
Data input woes
Later, I spoke with Dr. Feist during a break in the conference.
MH: Some people who have completed the PHPP training are still frustrated by the amount of data that has to be entered into the PHPP software. There are so many inputs, especially for windows that are not certified, and also for thermal bridging. Is there any way to simplify the number of inputs? Although we know it is technically excellent, is there a way to make it more user-friendly?
Dr. Feist: I completely agree with you. This is what we are aiming to do for the next step. To make it simple for the user is the most important thing. You have to have such a program, and we want to do that. The concept is, like it is already seen there, that you choose, say, a component, and you get all the data inputted. That is the concept that we want to follow.
MH: But we will not get Passivhaus-certified windows produced in the United States for many years.
Dr. Feist: Oh, I don’t agree. I think that will happen early. Because it’s just a question of whether this is asked from the market. If it is asked from the market, I’ve seen now that this is coming, there will be — like it happened in Europe. You know the first Passivhaus in 1991, there was no window. Nothing. There was nothing on the market. We built it just by handicraft with our own hands, and glued insulation on the window frame, and it was working. Then it took up until 1997, six years, until the first company went in. And after we had the first producer — that was the most difficult thing — after we had the first producer, there was suddenly all of the windows happening.
MH: Here in North America, we have Thermotech windows, we have Inline Windows, we have Accurate Dorwin windows. They don’t quite meet Passivhaus standards, and they aren’t certified. But for North American designers, it would still be nice if we could input the data for these windows with just one click.
Dr. Feist: You can do it. It’s no problem. The list of windows is open, and you can fill in your inputs. You only need the data.
MH: Is the data in a database somewhere that is accessible, or do you have to track it down yourself?
Dr. Feist: Of course I don’t have it. That’s a problem. That’s a thing I think is really necessary: you have to have some pressure on the producers so that they deliver the data.
MH: And it has to be accessible electronically so you don’t have to make a phone call each time.
Dr. Feist: And another problem is, it has to be trustable. That’s the reason that we started the certification. Very often a producer claims to have something that is really woo-woo-woo, and when you look, well… That was one of the most impressive situations that we have had — with the first mechanical ventilation with heat recovery system. They claimed to have 85% [efficiency], but when we did the measurements in a real building, it was 62 or something. That’s a big difference. So that makes it necessary to have somebody doing test measurements.
MH: The trouble is, even if there are forty Passivhaus projects in the pipeline, it’s not enough. The manufacturers won’t care. It’s not a market yet.
Dr. Feist: I know all that, because the history in Europe was the same. It was the same thing. The interesting thing is, and that’s why it can work, is that you are not dependent on the big manufacturers. You can work with a small or medium enterprise, and there are lots of them everywhere — and in the U.S.
That’s what I think we need most to motivate these guys to do that. Because it’s not only the Passivhaus market — imagine you have a window with these properties, and have it available on your market. It can be sold for refurbishment, for retrofit, and it could be used by other people who don’t build passive houses but just want to have a good window.
MH: We’re headed in that direction, but it will take a while.
Dr. Feist: The same like it was in Europe. We are not at the end in Europe now. There are still some big players on the market who don’t like it. That’s the next step that happens. Some big players don’t like it, who want to sell their old stuff. So they are blocking on the lobbyist level. That’s what’s happening now.
Do Passivhaus buildings have lower budgets for HVAC equipment?
MH: When I see this chart showing how the cost of HVAC equipment drops off suddenly when you improve the envelope — because you ‘don’t need a heating system’ — I’m not yet convinced. I haven’t yet seen it. If you still need an HRV, an air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps., or whatever your heating system is, and sometimes a solar hot water system — is it cheaper than an American heating and ventilating package? Not yet.
Dr. Feist: To be honest about that — You can’t look in the [rear-view] mirror to save that. This is what the development can do.
MH: You’re saying, we hope it will happen some day.
Dr. Feist: No, it’s not just a hope. If you look at the example in Lafayette [Louisiana], for example. They have just one split air conditioner unit for the whole house, where you normally use three or four. And that might be the right system for such a climate, because you have a solar warm water system. In this climate, maybe 85% or something is what you get from solar, and only a small amount [of water] you have to heat with electricity. Everything else you need is dehumidification and cooling, and that can be done with such a split unit, and the split units are quite inexpensive. And so this can be done with just one unit for the whole home. And this will be very cheap, of course.
MH: But it hasn’t quite reached the point where there is a savings for hardware — not yet.
Dr. Feist: At the moment. But I think the direction is the right direction. To invest a little bit more in the envelope in order to reduce these technical costs, and that will reduce all the costs in the supply line.
MH: In America, the most economical package of HVAC components are not being put together by Passivhaus builders, but by energy-efficient builders using mini-split heat pumps and either an exhaust or supply ventilation system with one Panasonic fan that draws only 11 watts. These systems have low development costs and good energy performance — just not Passivhaus performance.
Dr. Feist: Surely you will agree that the HRV — the plate heat exchangerDevice that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank. is not a very expensive a thing. This is just $200 or $300. If you calculate that back on an energy cost comparison, you will see this is a very cost-efficient measure.
MH: But in America, an HRV costs $2,000 to install.
Dr. Feist: It may not be available now at the price we need on the market. There I agree. This is again a thing — we have to put some pressure on the market to make these things available at a reasonable cost. It will take some time. It’s important to go that direction. It will reduce the overall electricity you need.
MH: It may or it may not. It will slightly lower your heating cost. But the HRVs use more electricity than a Panasonic WhisperGreen fan.
Dr. Feist: The efficiency of the heat-recovery system, using ECM motors, has increased very much. The systems we have now in Europe on the market, there is no question, they have a much higher efficiency than any heat pump could have.
MH: I’m not talking about heat pumps. I’m talking about ventilating a house. A supply or an exhaust system is much cheaper than a heat-recovery system, because you only need one fan.
Dr. Feist: It may be at the moment. You may be right, for the situation in the U.S. But the advantage of the heat-recovery system is in a cold or a hot and humid climate. It is a question of where you are. If you are somewhere in between, we can question whether heat recovery pays off. But if you are in a cold climate, there is no question, it pays off. And if you are in a humid climate, you have the possibility of dehumidification as well with a heat-recovery system.
MH: Not dehumidification. You can lower the humidity load caused by ventilating the house. It doesn’t provide dehumidification.
Dr. Feist: Yes, of course. What I also see, which has been proven to be a very good concept in Europe, that is the combination of the heat-recovery system with the heating or cooling supply. To have one box with everything integrated. It’s a better concept.
MH: The magic box.
Dr. Feist: You can call it a magic box. What is really important is, we all shouldn’t stick to just one kind of technology. What is important is the performance. The overall performance is what we need. Of course, we agree that we need ventilation for indoor air quality. Then there is of course the question of whether supply or exhaust alone will work. Maybe in some climates it would.
Last week’s blog: “Navigating Energy Star’s Thermal Bypass Checklist.”
- Martin Holladay
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