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No, the PHIUS+ and the PHI Passive House/Building Standards are not equivalent! Not anywhere close! If you are just getting into the passive building sector you need to be very clear on the high level differences to be able to make the best decisions for your project. This is what this short article is for.

Both standards trace back to the fantastic work that was done in the 70s and 80s in North America by the early superinsulation pioneers. They identified and codified each and every passive building science principle that we still refer to today. We all stand on the shoulders of many giants that came before us. I count among those Harold Orr, Rob Dumont, Oliver Drerup, Joe Lstiburek, Amory Lovins and Mike McCulley and those are just the ones I had the pleasure and honor to get to know personally. Without their help, sharing longtime experience and support for PHIUS, PHIUS+ would have never happened.

We all owe the German Passivhaus Institute a great deal for re-popularizing and putting passive building principles and standards back on the table in the early 2000s. I personally owe all the pioneers a lot. I began my work with Dr. Feist in 2004. He got me started. He taught me one-on-one and gave me the opportunity to become part of this incredibly significant movement.

I never meant to counteract PHI’s good work. But I did feel a stronger allegiance to science than to the PHI when I felt they were wrong exporting the German standard as is. We saw that it was leading to problematic design decisions and projects in North America. I did have to stand up and voice concern. I would do it again, anytime. And just to set the record straight, PHI, unlike some try to portray it, canceled contracts with PHIUS publicly after we let them know we could no longer work with them due to our concerns. That was their right and we took that risk. We at PHIUS feel responsibility towards the greater goal, and to supporting our building community by helping them avoid risk. It is too important that we succeed on the large scale, mainstreaming passive building.

Committed to the idea of passive building, we embarked on fixing the problems in the standard in collaboration with Building Science Corporation under a DOE grant. PHIUS+2015 Climate Specific Passive Building Standards were the result of that effort. Not just another passive building standard, but one specifically designed to address and fix the demonstrated shortcomings of the PHI standard when applied in a wide variety of different climates.

PHI was and is a one size fits all standard and uses energy targets and design guidelines that were originally developed for central Europe, a moderate heating dominated climate. The basic targets are specific to that climate and have not changed since PHI started exporting their design and verification system to other regions of the world.

PHIUS originally started out with that same approach and quickly learned that different climates had different combinations of heating and cooling requirements and that that combination should be used to inform more precise design guidance and energy targets. It became clear that the targets had to be specific to climate, had to incorporate cost considerations and had to be sensitive to building typology and occupancy to get the right answers in terms of comfort, return on investment, the most efficient use of materials and minimization of embodied carbon.

Think about it like a dart game. The old standard, before PHIUS re-calibrated the targets to where they really need to be to optimize for comfort, cost and carbon in buildings, is a one size fits all approximation. That is not very precise. It is getting you roughly into the vicinity of an optimal low energy design, but we can do so much better if we only make the targets more specific. The old targets are not anywhere granular enough to consistently guide you to the bullseye. Because of that it is a bit like shooting in the dark. You can get lucky but mostly you get scatter. If you are a building scientist who has additional high performance experience then you can go from that approximation and you might be able to fix the short comings. But why use an older approximation and pay building scientists to lend their expertise when all of us can use a more accurate tool that assures optimal design right away?

PHIUS+ 2018 aims to consistently deliver the bullseye: Optimal envelope design according to climate, cost, comfort, and durability through targets that are sensitive to building typology, occupancy, climate and cost sweet spot between conservation and generation…really pretty brilliant.

And it is working. Measured data on a variety of PHIUS+ projects and typologies shows on average a 93% match modeled versus measured. That is the best I have seen yet in the industry. PHI projects’ measured data shows a consistent mismatch between predicted performance as stated on the PHI certificate and actual performance by roughly 25-30%! Bullseye versus scatter. We are trying to hit a very tight carbon reduction target here and precision matters! We are running out of time. We better use the best tools we have, the ones that lead us to the best most accurate results.

The market has already recognized this standards evolution and innovation that PHIUS, the DOE, and Building Science Corporation have brought forward. During the last three years PHI certifications have all but stalled. PHIUS has certified 97%, 98% and 99% of all projects in North America, and a lot of them are large multifamily projects now.

Here is another example of difference in first cost: PHFA, the Pennsylvania Housing Finance Agency, funded PHI and PHIUS projects 50/50 during the first year. During that round the average additional cost for all projects resulted in 3-5% (PHI standard projects do not have built in cost optimization and tend to be more expensive than PHIUS projects). During the second funding year PHFA only funded PHIUS+ projects and the average additional cost dropped to negative 2% over standard baseline cost! No coincidence. This time 100% of all projects followed the cost optimized targets. PHIUS+ is working, it leads to more cost and carbon effective solutions. People are beginning to make that connection.

Back to the topic of false equivalency - a one size fits all approach cannot optimize for comfort and cost everywhere. It’s an attractive idea, but it can’t be done, it defies basic physics and math and those who try to claim that it can be done, to be blunt, are selling snake oil. PHIUS+ had to change its approach significantly to deliver on that promise but we got it done and the measured data and exponentially growing certification numbers as well as dropping first costs are proving us right.

And as such, PHIUS’ work represents the new, the courageous, leading the evolution of passive building principles, not just another insignificantly different flavor of passive. We have done significant, if not invaluable work over the past 5 years, to optimize the principles and standards and to take them to the next level. PHIUS+ standards keep the promise of comfort and resiliency in every climate but also the promise of cost and carbon optimization. It optimizes for energy and embodied carbon because PHIUS+ standards promote the right amount of insulation and the envelope measures don’t push back into diminishing returns.

PHI projects, while obviously way better than any other lesser energy efficient certification, are not dialed in. When getting into the nitty-gritty of passive building design, they represent a net loss in the effort to optimize for energy and carbon! They lead designers to over-insulate and to over-invest in the envelope typically which leads to overheating issues and unnecessary embodied carbon and cost in materials. They are neither climate nor building typology optimized for comfort.

Let’s not close our eyes. Let’s keep the eye on the prize. Let’s serve our greater goal, make sure we are as accurate and as granular and dialed in as we could possibly be with our design choices for every project we touch. Too much is at stake. We are up against a tremendous global challenge! PHIUS+ is proud to do its part. PHIUS+ projects represent the Tesla of the building world, a courageous super optimized driving machine with only an iPad instead of a dashboard anymore at a reasonable cost, let’s be as lean and mean as we can be in the building sector…for new and retrofit, join me in moving mountains!

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Share 39 16 Comments Prudence Ferreira

VP Sustainability + Resilience: Passive Building Practice Lead - Thornton Tomasetti

5y

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To illustrate the differences, here is a concrete example: For a high-rise residential passive house building in Vancouver BC, where the exterior envelope area to conditioned floor area ratio would be 0.7 or less (A 20-storey high rise envelope to floor area ratio would be in the ballpark of 0.5), the PHIUS+ target for annual heat demand (13.5 kWh/m2a) is more stringent than the PHI certification target (15 kWh/m2a for annual heat demand). However, for the PHIUS+ 2018 certification path, it actually takes less insulation and lower effective heat recovery efficiency for ventilation to achieve that 13.5 kWh/m2a than the PHI path would, thus subsequently less capital outlay because PHIUS+ modeling includes more realistic residential internal gains than current PHI modeling protocols, and because PHIUS+ has a more stringent airtightness target (0.08 cfm75 /0.06 cfm50 per sq foot exterior envelope) than PHI (0.6 ACH50). There is no right or wrong here, just different criteria, leading to slight differences in design strategies different performance and different costs. Depending on a project’s location and goals, either PHI or PHIUS certification paths may provide better alignment. 

Like Reply 5 Reactions 6 Reactions Tim Eian

Principal, Dipl.-Ing. Arch. (Architectural Engineer), Certified Passive House Designer (p3829), Assoc. AIA

5y

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Liebe Katrin, Deine Arbeit und Erfolge wären nicht weniger wert wenn Du im gleichen Atemzug die Arbeit und Arbeitsweise anderer nicht in den Schatten stellst. Tatsache ist, dass keiner der beiden Standards im Markt eine wirkliche Rolle spielt und darauf sollten wir uns alle konzentrieren. Ohne uns Passivhäusler kann man jegliche Klimawende vergessen und dieses Thema ist viel wichtiger als die mühsamen Heckenscharmützel. Schreib doch mal etwas positives und bilanziere CO2 im Vergleich zum Status Quo. Der ist der wirkliche Feind. Gemeinsam sind wir alle stärker in der Diskussion.

Like Reply 2 Reactions 3 Reactions Bronwyn Barry

Principal at PassiveHouseBB

5y

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Oh Katrin... it is desperately sad that after all these years you're still unable to let this go and move on. Eight years of relentless banging on about 'PHIUS is right - PHI is wrong' is such a tragic waste of your time and talent. Everyone has moved on - including PHI and their standard. All this proves is that you're still unable to differentiate your standard or organization from PHI's after eight long years. (This could be very easily and simply accomplished by changing your certification and organization's name, like you were advised to do years ago.) For those interested in an alternate perspective of this tragic history, I recommend the following source materials: PHCA's website hosts a history, including the legal tussle between PHIUS and PHI: http://passivehousecal.org/history PHI's version of events: https://passivehouse-international.org/index.php?group=1&level1_id=76&page_id=246&lang=de For those interested in an unbiased comparison between the two standards, I recommend you either conduct your own independent research and use source material (rather than relying on  those with a clear conflict of interest) or look to third party reports such as this one funded by NYSERDA: https://www.nyserda.ny.gov/About/Publications/EA-Reports-and-Studies/Energy-Efficiency-Services-Reports PHI has continued to support efforts to promote Passive House in the US via an active network of national and regional affiliates and organizations, listed here: https://passivehouse-international.org/index.php?page_id=249. Notably, PHI has not made ONE SINGLE PUBLIC STATEMENT either for or against PHIUS since 2011. They're too busy focused on supporting a global network of partners and scaling projects. Wouldn't it be great if PHIUS could do the same?   I wish you and PHIUS much success in scaling your efforts and encourage you to finally give up on these desperate attempts to stake out high holy ground. We need everyone at the helm, driving the adoption of better buildings here in the US, before ALL ground is rendered uninhabitable.  [Comments here are my own and do not reflect the opinion of either PHI or any other organization with which I am associated.]

Like Reply 6 Reactions 7 Reactions Fin MacDonald

ESG | Zero Carbon | Sustainability

5y

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Too many people don’t know this. Especially in Canada.

Like Reply 1 Reaction 2 Reactions Norbert Hennrich

I create loyal customers by forging authentic relationships | Service Manager

5y

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In my opinion, it makes total sense to take various needs for heating and cooling into the design equation.

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