A Passivhaus Rebuttal: In Defense of the Standard
A Seattle architect responds to Holladay’s keynote address about Passivhaus ‘missteps’
By Mike Eliason
To preface: these thoughts are my own and draw from the Certified Passivhaus Consultant training, studying European Passivhaus projects (occasionally documented on our blog), modeling projects and dissecting PHPP with my brute force collaborative cohort, Aaron Yankauskas. They are in no way endorsed by PHIUS, PHnw, PHA or the PHI in Darmstadt…
Martin gave the kickoff address for the 2nd 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. Northwest (PHnw) Spring Event. Unlike most kickoff addresses, his pointed out missteps of the North American Passivhaus movement. Amazingly, instead of deflating all 170 attendees, reactions were varied — agreement, disagreement and probably even a little rage! Attendees were discussing aspects of his address well beyond the meeting — a testament to issues with which many have struggled. There was a brief question and answer period, but no one successfully challenged Martin.
After the event, I was cornered by Martin to discuss my thoughts. Unfortunately (or perhaps fortunately…) my carpool was antsy to leave, so we weren’t able to get into as deep and fruitful a discussion as warranted. However, Martin has generously permitted me to address my thoughts on his thesis for the benefit of GBAGreenBuildingAdvisor.com. What follows are the central themes of his address and my own “musings of a design geek” for each. Like everyone at the meeting, I’ll probably be highly unsuccessful in challenging Martin, but appreciate the opportunity to expand the dialogue.
Martin began his address with what he likes about Passivhaus: that it stands on the shoulders of North American giants, sets a high bar for airtightness and has created a significant buzz that “energy nerds” haven’t seen in a long time (or maybe ever). He then proceeded down his list…
Misstep #1: “Passive” is a problematic term and the direct translation “Passive House” is confusing
Passivhäuser (Passive Houses) employ active mechanical ventilation and require active heating components (albeit very small). If comfortable with a lower setpoint, throwing a dinner party or borrowing the neighborhood kids — it’s entirely possible to forgo any active heating and live in an entirely passively heated house. The term isn’t completely accurate, but at this point changing the terminology would only create additional problems.
I abhor the direct translation of Passivhaus! Whenever I talk to someone about Passive House (Passivhaus) – it devolves into a discussion of something tried in the ’70s, or a semantic argument with passive solar house designers. Every Passivhaus consultant knows this story, and that alone should warrant reconsideration. In German, Haus is slightly more nuanced than House — and non-residential buildings offer greater energy savings than residential projects. Plus, we don’t call the Volkswagen the Public’s wagon (although we happily obliterate Köln as Cologne!).
Misstep #2: Häuser ohne Heizung (houses without heating) is a false statement
There has been a lot of inconsistency in the way Passivhaus projects have been represented online and in print – though this isn’t the fault of the PHI, and I think there are other contributing factors. First, I believe this is another case where direct translation fails – Heizung could mean radiator and Passivhäuser simply don’t need them. Second, many Passivhaus owners just never utilize their heating systems. However, most require some degree of space heating, and it would certainly be better if consultants were honest about this and persistent in correcting media errors.
Misstep #3: Space heat delivered through ventilation duct
There is no requirement for space heating to be delivered through the ventilation duct – though this was the classic definition, which was apparently altered to appease the Scandinavians. If towel warmers, localized radiant heating or mini-splits are preferable to deliver space heating – they’re all acceptable forms. I’m not an engineer, but am really drawn to the decoupling of ventilation and heating as championed by Kiel Moe and Transsolar.
Misstep #4: 15 kWh/m²a (4.75 kBTU/ft²a) is too difficult and arbitrary
As was relayed to me recently, the 15kWh/m²a heating limit is the point when traditional heating systems could be eliminated and the cost of implementing Passivhaus became affordable. This limit wasn’t arbitrary for central European climates at the creation of the Passivhaus standards, but that point on Dr. Feist’s graph may shift in North America. After dissecting PHPP — that limit could very well be lower compared to Europe.
The argument that achieving the specific space heating demand is too difficult rings hollow. By keeping the standard difficult, it will push product innovation, designer innovation and maybe cause people to rethink whether building single family homes makes sense in certain climates. Who wants to wait 10 years for North American manufacturers to catch up to where E.U. manufacturers are now?!?
Regarding the extreme R-values — there are only a handful of built Passivhäuser in North America, and several were shoehorned through PHPP after being designed, resulting in absurdly high R-values. Basing the difficulty of achieving the specific space heating demand on these first projects is a biased sample. One of the pursuits of
Over the last year, I’ve been combing European Passivhaus projects and have yet to find an envelope assembly greater than R-80 — even with climbing huts high in the Alps or smaller houses in regions that get little sun. PHPP consistently shows that it’s actually easier to achieve Passivhaus in the United States. Figure 2 (see below) shows the resulting specific space heat demand across different cities by HDDThe difference between the 24-hour average (daily) temperature and the base temperature for one year for each day that the average is below the base temperature. For heating degree days, the base is usually 65 degrees Fahrenheit. For example, if the average temperature for December 1, 2001 was 30 degrees Fahrenheit, then the number of heating degrees for that day was 35.. The blue line is Katrin’s house modeled in CPHC training and migrated to North American cities; the red is Katrin’s house migrated through Europe. For comparative HDD ranges, the EU numbers trend significantly higher than North America.
What this says to me is designers and consultants in North America need to get creative and test the limits of PHPP. European designers don’t seem to have this problem, even though they are at a solar disadvantage. To further illustrate my point, the Österrichhaus in Whistler, B.C. (HDD: 8,000+) has no envelope assembly higher than R-54. That speaks volumes on how an integrated and oft-tested approach makes a significant difference.
Misstep #5: There is a lack of cost-effective feedback loops within PHPP, so Passivhaus designers just keep adding insulation — even if it’s beyond the cost of photovoltaics
Yes, there are people building excessive assemblies. Strangely, they would rather add insulation to their PHPP model than evaluate if the form, windows, openings or orientation need to be adjusted – even if doing the latter optimizes their assemblies. I don’t think this is a Passivhaus misstep, but a user one – PHPP is simply a spreadsheet and adding additional pages is not difficult. We’ve already seen ‘control panels’ allowing rapid study of assemblies and form. Much like the proliferation of cell phone applications - I imagine (hope?) we’ll soon see PHApps (Passivhaus Applications) – PHPP add ons for rapid testing, cost analysis, etc. Additionally, any designer could do a quick takeoff and check against cost of photovoltaics at any point along the way if so motivated.
Regarding insulation versus the cost of PVs — it seems PHPP doesn’t reward the use of grid-tied photovoltaics because this still leads to CO2 emissions through transmission losses over the course of the year. This can be seen in the energy utilization factors counted against the 120 kWh/m²a max. The specific primary energy demand is really a metric for reducing CO2 emissions of the building to levels agreed upon at the 1992 Earth Summit. To take this a step further — our interest lies in adding PVs that exceed net zeroProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations., resulting in carbon reducing/plusenergie buildings.
Misstep #6: Small house penalty
On the “difficult to achieve”-iness of really small homes: I believe Alex Boetzel summed it up best: the German mindset regarding the difficulty with small houses is maybe you should build a multifamily house instead. There is a lot of truth to that — and maintaining the difficult standard might force the owner to determine if that is really the most efficient use of resources. We already know that EUI (Energy Use Intensity) is a decent metric for comparative analysis of non-residential typologies and that it’s horrible for residential ones. Martin mentioned a preference for per person energy limits — which actually makes sense, but seems very difficult to enforce and may cause issues for growing families. In training, we were told that houses over 4,000 sf would get the Mantle treatment (*) — although on a certain level, I believe this should apply to second and/or rural homes as well, and maybe that asterisk should be closer to 3,200 sf.
Misstep #7: The standard doesn’t distinguish between energy sources
I agree up to a point, however PHPP does distinguish between energy sources for source energy (there are utilization factors for electricity/pellet/natural gas/etc) — it just doesn’t offer a “credit” for utilization of PV or wind. And again, this speaks more to the 120 kWh/m²a as a CO2 limit than anything else.
Misstep #8: Change the standard for North America like was done in Austria
Martin stated the Austrian government changed the standard, although with my broken German it appears this is only partially correct. In Austria, there are two routes to Passivhaus certification, through the Passivhaus Institut, or through a state run program which appears slightly harder than the first route. For the state-run option, the project needs to meet 10 kWh/m²a based on bruttogrossflaeche (gross square footage) instead of the PHI’s 15 kWh/m²a, based on Treated Floor Area. I’ve yet to see a house with that large a difference between the two reference areas.
Martin also advocates for climate specific standards – and when cornered, I jokingly stated, “the standards are climate specific – it just so happens that the standard is the same across all climates!” Semantics… Sure. But it’s also because I believe given the right orientation, envelope, designer, etc. – it is possible to achieve the specific space heating demand in Minneapolis, Vermont or Miami – without needing an assembly over R-70. The Bagley Nature Center in Duluth came pretty close with an R-85 roof. It even utilized North American windows and Cardinal 179’s triple pane — I would love to use this glass, Cardinal just needs to improve the U-value and SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. by about 10%. Changing the standard to be easier in colder climates would effectively be a bonus for living in a location that requires more energy – and given our research, that’s not something I believe to be necessary.
Fervent discussions continue
In the end, everyone was (is) discussing Martin’s address with fervor — and it was stimulating to talk to those that agreed or disagreed and determine why. A lot of the things Martin and others see as issues or missteps — I believe to be misconceptions. I think as we become more familiar with the nuances of PHPP, a lot of these issues will sort themselves out. And hopefully, Aaron and I will have the opportunity to show that in the near future. If we do, you’ll find it on our blog.
Read Martin Holladay’s address: Are Passivhaus Requirements Logical or Arbitrary?
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