Many Cereals, One Cereal Aisle

GW

Graham Wright

The PHIUS+ standard has evolved on a very different path than the PHI standard, and they are in no way equivalent. That’s by design, based on deliberate decisions and building science, with a focus on cost-optimization and climate specificity. Still, confusion remains in some corners of the marketplace, confusion that is worsened by articles like the one that appeared in BuildingGreen a few weeks ago. (You can also read Chris McTaggart’s rebuttal at Building Green.)

Here, to provide a full accounting of how and why the standards are different, is PHIUS Senior Scientist Graham Wright. 

At the Seattle PHIUS annual conference in 2017, one of the keynote speakers, Doug Farr, came to a line in his speech saying “many boxes, one cereal.” The point he was making (as I heard it) was that there are a whole lot of “green” and “sustainable” and “high-performance” building programs, badges, and ratings all competing for attention or mind-share, and that this was not good because it made for a diffuse effort toward solving our sustainability problem. What you have, he said, is like a whole bunch of different cereal boxes on the shelf, but inside it’s “all kind of the same stuff.” It would be better if all these different outfits would get together to advocate with one voice.

While I agree that joining forces sounds like a good idea in general, personally I think he got the rest of it almost exactly backwards. For one of the other keynote speakers, Eric Werling, one of his major points was that the details matter. In terms of cereals, it is not all the same stuff — muesli is different from oatmeal or cornflakes or Cap’n Crunch®. We do not have many boxes — one cereal, rather we have many cereals, one cereal aisle. The bacon and hash browns are in another aisle. For the building industry the name of that aisle is probably “Green Building,” I think that’s the broadest and most recognizable term for what we’re talking about, and could encompass high-performance, sustainable, resilient, natural, living, green, healthy, net-zero, and of course, passive. Things it does not encompass but at most only overlaps with would be for example: secure, co-housing, modernist, Usonian, affordable, vernacular, brutalist, social, connected, low-tech and so on — these are quite different “programmatic” considerations and have their own aisles in the pan-galactic building store.

One of these things...

One of these things…

In the case of cereals the reason there are different kinds is because tastes differ, but also because values differ — if I value yumminess above all I will get Cap’n Crunch, but if I value avoiding the family curse of heart attack above all, I will get the oatmeal. In Green Building even more so, we have different programs because of differences in truly heartfelt values. Both builders and their clients bring different values to their meetings — if I am concerned about not polluting the environment, respecting brother salmon, I will go into natural building; if my children are prone to allergies I will look for healthy-home builders; if I

...is not like the other.

…is not like the other.

hate paying utility bills I will go for net-zero, and so on. So it is useful to have badges and rating systems corresponding to these different values or priorities, for matchmaking between builders and buyers of buildings.

Back to the common ground for a moment. It has dawned on many people I think that these different aspects of green building are connected, by a general crisis of climate and sustainability with industrial civilization, that we do have common ground in making the point that we must stop using fossil fuels and putting CO2 and other pollutants into the environment and doing so much mining, if we expect to also keep getting things like fish and wood and well water out of it at the same time, and that we might be able to form a chorus of voices calling for this.

I know of three such separate “common voice” efforts (heh) arising in the last couple of years:

PHIUS has joined Shift Zero, which has come together around the Architecture 2030 definition of zero net carbon buildings. Washington State already has one of the strictest state building energy codes, more stringent than IECC 2015, according to ACEEE, but at the initial Shift Zero summit meeting, the item “Roadmap to a Net Zero Building Code” was chosen as a major focus. This is relevant to us for two reasons: 1) We believe passive building should be on that road! The PHIUS vision statement is to “make high-performance passive building commonplace,” which it would be if it was Screen Shot 2019-08-27 at 1.46.00 PMcode. Also, 2) although it’s not spelled out in the short mission statement on the web site, the long version in the business plan speaks of the climate crisis and how passive building can both mitigate and adapt to climate change. We concur that as a society overall we must get to Zero, not just net-zero but Absolute Zero in terms of emissions, or 100% renewable energy to put it the other way. (The PHIUS Technical Committee has already taken this definition of Zero Net Carbon into consideration for our PHIUS+ 2018 standard update.)

Moreover, we are pursuing an ANSI-approved passive building standard, via the ASHRAE Standard Project Committee 227P. Participation in Shift Zero should allow us to both contribute to and be informed by a Shift Zero effort on Washington State code.

Our aim here is not to “get PHIUS written into WA code”, nor to “get an ANSI stamp” on PHIUS+ 2015 or even 2018, but to develop something that is both rigorous and more flexible, and of more enduring value. Our current standard is mostly performance-based, that is, based on modeled energy use. This requires modeling protocol, modeling software, and training in using it, for both project planners and verification/enforcement caseworkers. The vision for the ANSI/ASHRAE passive standard is that it would use a combination of prescriptive, performance, and outcome-based compliance paths to support the whole range of project scales – from small projects in backwater jurisdictions with few planning or enforcement resources to large projects in capitols that could take on custom cost-optimization studies. The value of PHIUS+ lies not only or even mainly in the current criteria but rather in the principles and methods underlying them, such as the priority on passive measures and conservation, the constrained cost-optimization for the heating and cooling criteria or the fair-share and national-solidarity principles for total energy use.

The “A” in both ASHRAE and ANSI stands for American. The ANSI mission statement is U.S. focused and the web page has a U.S. flag image. But the ASHRAE mission states pointedly that while they started out in U.S. they now have worldwide membership and global services, advancing sustainable technology for the built environment.

An ASHRAE passive building standard then, ought to be serviceable globally (at least in those parts of the globe that have building professionals.)

In my opinion PHIUS brings a track record of experience and care to this effort, as well as integrity, and humility.

As most of you will know, we started out practicing an “International standard” from PHI in Germany, applying it in the U.S. Our first major adaptation was in 2012 with the addition of greatly expanded quality assurance requirements from U.S. DOE programs. We found that the U.S. building industry simply needed a lot more guardrails on quality. This was in essence a cultural adaptation, as was our early support for the inch-pound unit system. Our second major change was a climateadaptation, in 2015 with the elaboration of the climate-specific criteria for heating and cooling.

To make a long story short, we found that the PHI heating and cooling criteria became disconnected from the principle of economic feasibility that supposedly underlay them, when applied to most climates in the U.S. and Canada, and we set out to redeem that promise. That disconnect affected both the heating and the cooling criteria in different ways, and was apparent in the data of PHI’s own climate parametric study of 20111. As a result of that study, PHI indeed adjusted their cooling criteria, adding to the (not climate specific) fixed base cooling demand a substantial and variable allowance for dehumidification (fair enough, there are not many passive measures that do this.) But the heating criteria still only made sense in one climate, and this was never fixed. Most of the U.S. being heating-dominated we thought that important and so went to work on it in 2013-14.

To make the story just a bit longer, what I would call the first-generation passive builders were splinter group off of the “passive solar” or “solar home” movement in the 1970s. Their differentiation was less mass-and-glass, less gain, more insulation, build light and tight. They tended to speak of “superinsulation” to differentiate themselves from the passive solar people, but passive building really is a better word for it; it’s not just about insulation. The canonical work summing up the first-generation ideas is The Superinsulated Home Book. Their concept of what counted as such a home was a little vague – they speak of reducing the heat losses until the building really starts to “act different” – but the definitional ideas included both low annual heating bills and low peak heating loads, that is, very small heating system capacity required, even to the point where a dedicated furnace was no longer needed; “just steal a little heat from the water heater.” This aspect I think forms the appeal to the heart of the “passive-house flavor” of green building cereal — the “self-heating building,” the “furnace-free house.”

The Superinsulated Home Book

The Superinsulated Home Book was published in the early 1980s, just as the bottom fell out of the solar movement stateside. The torch passed to Europe, and when PHI wrote their definition of a passive house, they focused on that low peak heat load concept and drew a line in the sand on how low it should be — basically, the point where the ventilation and heat distribution systems could be combined. This was reasonable and it does give a target number for design heat load, about 10 W per m2 of floor area, that would apply everywhere, at least in any heating-dominated climate. But when it came to writing certification criteria, an alternate compliance path was added by which one could meet a corresponding annual heating demand. Corresponding that is, in the climate of central Europe. This is the notorious 15 kWh/m2 or 4.75 kBtu/ft2, per year. If a building was designed to meet a peak of 10 W/m2 in central Europe, this is the resulting heating demand.

The problem, I say the glaring problem, is that that alternate criterion doesn’t correspond to the peak load definition in other climates. Again, this is according to PHI’s own study from 20111-2012. They took a study building, moved it around to a lot of different climates, adjusted the upgrades to meet the 10 W/m2 peak heat load definition, and plotted the resulting annual heat demand. It varied a lot, generally increasing as the annual average temperature got lower, but there was a lot of scatter, because annual temperature and peak load design temperature aren’t necessarily that closely related, it depends a lot on how close you are to the ocean.

Nevertheless, the PHI heating criteria remained the same two numbers for everywhere, either 10 W/m2 peak, corresponding to their definition, or 15 kW/m2.yr, which mostly doesn’t. Why? I have always darkly suspected that it is because in continental interior climates, the design temperatures for peak heating load are quite low, making the 10 W/m2 much the more difficult of the two numbers to meet. I think they could tell that it would be impractical for single-family dwellings, even attached like a townhouse end unit, to meet the ostensible definition, and so left the 15 kWh/m2 alternate in there as a close-enough cheat. I say it drives bad design, over-glazing, because solar gains do more to lower the annual heat demand than the peak load. (We showed evidence of this in our PHIUS+ 2015 development report published by NREL.)

Therefore, as I mentioned above, after a few years of applying PHI’s standard in the U.S., and noticing this lack of integrity with the heating criteria, we embarked on a reconsideration of the whole thing, in 2013-14. To my recollection, it just so happened that PHIUS and PHI both officially made standards announcements on the same day, March 15, 2015. PHIUS did make changes to all 3 “pillars” or marquee-level criteria — space conditioning, primary energy, and air-tightness. But, as evidenced by what got elaborated, it was clear that PHI had spent most of 2014 working on primary energy, the big change was the new and more nuanced Primary Energy Renewable (PER) metric, while PHIUS had spent most of that time working on new and more nuanced heating and cooling criteria. To go ahead and put a fine point on it, PHIUS took more care in 2014 with the core concept — the passive measures and how far to push them to drive down the heating and cooling loads.

(I must say it was irksome to get comments like, “sounds like PHIUS+ 2015 is just about bolting on some PV.’ when all we had done was put PV on the same footing as solar hot water, while PHI had spent the whole year working on renewable energy.)

Therefore, I think it is fair to say as a general matter, PHIUS has learned the importance of both “cultural” factors and climate factors to the development of passive building standards, and will bring this to an ANSI/ASHRAE standard development project. The approach to climate I think we have a fairly good handle on, and the multiple compliance options mentioned above should be able to accommodate various “building delivery processes”.

Lately it seems, we hear a lot of glossing over the differences between PHI and PHIUS. “It’s all good” kind of talk, “the differences are for nerds” and the like. At some level, this is fair enough. Yes we heart the furnace-free house, yes we like the EN/ISO 13790 monthly method for annual heating and cooling calculation and the EN 12831 for peak heating load, no we are not trying to be “lite” in general; honestly we get as much “we’re going with PHI because it’s easier” as the other way around.

But at some level the details do matter. In particular when it comes to talking about building energy code, mandatory, enforcement, permits approved or denied, people are going to want to know quite specifically what are the rules, yes?

Let’s think about the most simple and straightforward proposal I’ve heard for a building energy code: enacted in a skit by Henry Gifford and Chris Benedict of New York City, they propose the code consists of just a criterion on the design heating system capacity, that is, a peak heat load. Even with just that, you can see it would take some pages to spell out: by what method or methods of calculation? Do the methods vary for residential versus nonresidential buildings? Are solar gains or thermal mass to be credited with reducing peak loads? By what method are the design temperatures to be determined? Shall these be historical or forward-looking at climate change? Who is qualified to perform the load calculations and to review them? Does the criterion apply zone-by-zone or to the building as a whole? What if I have multiple buildings served by a central system?

So yes, at some level it is fair to say, PHI and PHIUS that is blueberry muesli, all good. But when it comes to the Food and Drug Administration, and to many customers, it is going to matter what is in those blueberries exactly. Are those real blueberries or fake f@#$% blueberries? Are the real blueberries GMO Roundup-ready blueberries or organic blueberries?

At PHIUS I think we have demonstrated some care and forethought in adapting our program and standards in the direction of suitability for incentives and codification in North America, while remaining faithful to the heart of the passive building concept. We will bring this experience and intention to the development of a more widely/globally applicable ANSI/ASHRAE Passive Building Design Standard With Path to Zero Emission or 100% Renewable Energy Society or the like.

ASHRAE requires a fairly public and transparent process and we seek the participation of the best building energy experts anywhere who find this vision agreeable — including PHI, with just one proviso: that 15 kWh/m2 everywhere is not going to make it, that is fake blueberry and we cannot have it in this muesli. If you can let that one thing go at last, the possibilities for fruitful collaboration open up. As those conveners I mentioned in Bonn, Seattle, and Portland have been suggesting, let us get the oars in the water and try to row in a more coordinated way at the goal of a Zero emission / 100% renewable built environment.

1 Schneiders, J.; Feist, F.; Schulz, T.; Krick, B.; Rongen, L.; Wirtz, R. (2012). Passive Houses for Different Climate Zones. Passive House Institute and University of Innsbruck.

 

 

Comments on climate-specific standards study now open

ClimateSpecificColor
In cooperation with Building Science Corporation, under a U.S. DOE Building America Grant, the PHIUS Technical Committee has completed exhaustive research and testing toward new passive house standards that take into account a broad range of climate conditions and other variables in North American climate zones and markets.

This report contains findings that will be adapted for use as the basis for implementing climate-specific standards in the PHIUS+ project certification program in early 2015. Furthermore, as materials, markets and – climates – change, the PHIUS Technical Committee will periodically review and adapt the standard to reflect those changes.

  • We invite formal comment on the science. Please use this online form to submit. Deadline for formal comment: January 16, 2015.
  • Formal comments will not be public, and are for Tech Committee review only. (The Tech Committee or PHIUS staff will contact you for permission, should we be interested in publishing your comments.) All formal comments will be reviewed, but we cannot guarantee an individual response.
  • Passive House Alliance US Members: An online informal discussion forum is available to all members. The forum discussion will be visible to the general public, but only PHAUS members can make comments. Comments on the discussion forum are not guaranteed to be reviewed by the Technical Committee.
  • If you are not a PHAUS member, use the blog comments section below. Comments on the blog cannot be guaranteed to be reviewed by the Technical Committee. To ensure Committee review, use the online formal comment form.

Passive house history (PHistory) Part I–North American roots

In 2002, when I set out to build my own passive house as a proof of concept, I eventually selected a site in Urbana, Ill. I had was working in Chicago at the time, but Urbana made sense for several reasons: it offered affordable land, the city and its citizens have a progressive history in terms of environmental issues, and it is home to the University of Illinois at Urbana-Champaign (UIUC) and all the resources that a research institution offers.

What I’ve learned since then is that pioneering work at UIUC decades ago actually helped spawn what we now refer to as passive house. It’s a fascinating history, and one worth sharing here. To all the pioneers out there—weigh in with additions and clarifications. I hope you enjoy!

–Katrin

Passive house describes a set of design principles and defined boundary conditions that—if applied holistically—lead to a building that remains comfortable with only minimal active heating or cooling during extreme climate conditions. The specific boundary conditions determine the design of the thermal envelope. Minimized mechanical systems result from specific space conditioning energy consumption and peak loads: quantitative, measurable performance-based energy metrics for homes and buildings.

The underlying passive principles were pioneered and formulated in the United States and Canada in the 1970s and 80s following the oil embargo and resulting energy crisis of 1973. By 1986 the noted physicist William Shurcliff was able to summarize what at the time he considered a mature and widely adopted technology. He described the five main principles of superinsulation also known then as passive housing in his article int the 1986 Energy Review”:

a) thick insulation
b) airtight construction
c) prevention of moisture migration into cold regions within the walls, and other regions where much condensation could occur
d) optimum sizing of window areas
e) a steady supply of fresh air

He goes on to describe in detail the necessary components: triple pane windows, heat recovery ventilators, thermal bridge free and airtightness design strategies, vapor retarders, a small wood stove as a heat source for the entire house etc.

In essence, what Shurcliff termed “Superinsulation” was essentially identical to passive house as we know it today.

Council Notes–the University of Illinois’ Small Homes Council periodical–featured the Low-Cal house back in 1981. Plans and energy modeling details were published in a standalone paper years earlier.

 

Where it started: Back to the future

Urbana, Illinois. The same Urbana that—by Kismet—is today home of PHIUS. In the early 1970s, a group of engineers and architects at the University of Illinois Small Homes Council (now knows as the Building Research Council) began experimenting with highly insulated envelope components. The group included included Wayne Schick (who coined the term superinsulation), W.S. Harris, R.A. Jones and S. Konzo. Their research culminated in the concept of the Lo-Cal (for low-calorie) house in 1976. (You can still buy original publications about Lo-Cal by the Council and Schick  here. And Building Science Corporation’s Joe Lstiburek writes about it here.) Lo-Cal was projected to save 60% in energy consumption compared the most efficient design promoted at the time by the Department of Energy.

A young architect working with the Council at the time, Mike McCulley, built four Lo-Cal houses in Urbana and Champaign. The Council monitored and evaluated them for performance, and these projects gained some attention from press outlets around the country.

An article about one of McCulley’s Lo-Cal houses appeared in the 1982 Louisville Courier-Journal. (Click to enlarge)

This Illinois group’s ideas greatly influenced a Canadian group of engineers working on the Saskatchewan Energy Conservation House (well chronicled in 2009 by Martin Holladay in Green Building Advisor–“Forgotten Pioneers of Energy Efficiency). They succeeded in reducing losses and peak loads even further. The peak load of the Conservation House in this extremely cold climate was designed to be approximately 1.5 W/sqft, equivalent to the best peak loads we are seeing in today’s passive houses in similar climates.

…A NEW LABEL–PASSIVE–IS BORN

The concepts gained momentum in both countries, spawning prototypes and buzz at building conferences.  The press and the public took notice. The term superinsulation was evolving as the most commonly used label for this set of principles in a growing North American high performance building community.

In 1980 William Shurcliff published one of the first books on the topic, called “Superinsulation and Double Envelope Houses.” Shurcliff, an accomplished physicist who took up the subject after his retirement from Harvard, went on to publish many books on the passive solar and superinsulation concepts in the late 1970s and early 1980s. In fact, Shurcliff appears to be the first to have labeled the new concepts “passive house” in his 1982 self-published book “The Saunders-Shrewsbury House” [Shurcliff, 1982]. It describes direct-gain and indirect gain passive houses. Later in a 1986 article he states that “a superinsulated house is really a special type of a direct-gain passive solar house.”

Because many architects and builders felt that superinsulation was too narrow a term, passive housing started to be commonly used interchangeably with “superinsulation.

Regardless of labels, Shurcliff states that by the mid/late 80s there were tens of thousands of homes built in the United States and Canada (as many as in Europe today!) to these design specifications. By 1982 a movement had formed. Thousands of building professionals were traveling to conferences taking training to learn the techniques. Construction of such homes was growing “explosively” as Shurcliff puts it in one of his early books in 1980 (Superinsulated Homes and Air-to-Air Heat Exchangers). The Canadian government offered free builders trainings. Widely read magazines sprung up, amongst them the still today well known and respected Energy Design Update.

SOUNDING FAMILIAR?

Shurcliff defined a superinsulated house as follows: “…a) receives only a modest amount of solar energy […], and b) is so well-insulated and so airtight that, throughout most of the winter, it is kept warm solely by the modest amount of solar energy received through the windows and by intrinsic heat, that is, heat from miscellaneous sources within the house. Little auxiliary heat is needed: less that 15% as much as is required in typical houses of comparable size built before 1974.”

He further explained: “The 15% limit on auxiliary heat […] was chosen because a house that conforms to this limit can get through the winter fairly tolerably even if auxiliary heat is cut off entirely. Specifically, the house will never cool down to 32 F. […] In summary, the basic strategy of superinsulation is to make the house so well-insulated and airtight – so conserving of heat – that it is kept warm almost entirely by heat that is received informally and is free.” (2)

What’s striking is that the 15% maximum limit cited for the annual heating demand compared to standard construction at the time is very close to the energy metric that defines today’s passive house criteria: 4.75 kBTU/sqft yr!

To explain: Comparing current contemporary home energy consumption for heating to the energy consumption of a home built in 1970 one finds that the reduction in heating energy consumption from 1975 to 2006 is approximately 17% (see DOE graph). In 2005 a typical home in the state of NY consumed approximately [34.76 kBTU/sqft yr] according to the EIA for heating. Increasing this energy consumption by approximately 20% (MEC-IECC Graph) results in 41.71 kBTU/sqft yr for a home built in 1974 (before the MEC took effect). 15% of that total value equals 6.25 kWh/sqm yr, (19.7 kWh/sqm yr) an energy metric limit very close to the current Central European passive house metric of 4.75 kBTU/sqft yr which was codified in the late 80s to early 90s.

Note that most passive houses at the time were built in quite a bit colder climates of the US and Canada. The colder climate boundary conditions are likely reflected in this slightly higher annual heating demand limit (as a direct result of greater peaks).  Peak load then as it is today was understood to be the determining factor. Another curious historic trace of those early superinsulation experiences describing very low load homes similar to the European secondary passive house standard peak load threshold of 10 W/sqm exists in the International Energy Conservation Code (IECC). The current International Energy Conservation Code (IECC) still recognizes extremely low load homes, defining them as homes with a peak load equal or smaller than 1 W/sqft (10 W/sqm) for heating in section 101.5.2 [International Code Council, 2012] effectively exempting them from having to have a conventional auxiliary heating system. The code assumes in this case that the intrinsic heat sources are equal to the tiny peak losses aka no need for additional heat. According to the Code Council the IECC is the successor of the first 1975 Model Energy Code (MEC), from which this definition was originally adopted!

Shurcliff goes on to describe the performance of such houses in winter:

“1. The typical annual heat requirement on the auxiliary heating system is so small that the annual cost is almost negligible compared to the main household expenses […] 2. The occupants benefit from the absence of drafts, cold floors, and cold spots near windows. 3. Because the south windows are of modest size, little or no sunny-day overheating occurs. 4. Anxiety as to possible failure of the auxiliary heating system is minimal because the rate of cool-down is so low (a fraction of a degree per hour) that the house can easily ride through a 24-hour period with no auxiliary-heat-input. 5. Thanks to the use of an air-to-air heat exchanger, humidity tends to remain in the desirable 40-60% range and there is a steady inflow of fresh air (at, typically, 50-150 CFM, or about half a house volume of fresh air per hour). 6. Little outdoor noise penetrates the house.”

He also notes that the orientation of the house is not critical to the concept. He says that the house can have almost any orientation, unlike only passive solar-heated designs that had to be oriented within 25 degrees of south.

REFINEMENT

The technology matured and the market began to follow. Energy Design Update published an entire edition in 1987 as a consumer guide devoted solely  to the many air-to–air heat exchangers. The Canadians appear to have taken the technology lead in the 1980s. Shurcliff credits Harold Orr’s construction type from the Division of Building Research of the Canadian National Research Council to be the most widespread type being built in North America.

In 1984 young J.W. Lstiburek and J.K Lischkoff publish a book called “A New Approach to Affordable Low Energy House Construction,” further advancing various aspects of passive housing and related sciences. The “Superinsulated Home Book” by Ned Nissen and Gautum Dutt published in 1985 is the most advanced construction and detailing book in the industry at the time. The book even presented a detailed chapter on the theory of energy balancing and sample calculations for low load homes, explaining how to balance losses and gains to arrive at a design with an extremely low balance point temperature.

In 1988 Shurcliff concluded in his book “Superinsulated Houses and Air-To-Air Heat Exchangers” [Shurcliff, 1988] that this type of energy efficient home construction is here to stay and that one might see some further improvements in window technologies, vapor retarders, more efficient heat exchangers and compact minimized mechanical systems, “…but that there is no need to wait for such refinements. Superinsulation is already a mature and well proven technology.”

That was 1988, and the future of superinsulation/passive housing in the United States was bright, but…

See the passive house history Part II

 

 

 

 

The anchor of the passive house principle

It’s been some time since I posted the first blog — “15kwh Is Dead, Long Live 15kwh.” It sparked a lively debate and discussion. That’s really good.

It also is clear that there is at least some confusion about what the core principle of passive house is. So, I will give it another shot before we move ahead with the tech committee and workgroup efforts on fine-tuning the standard for North American climates later this month. Again, as outlined in a webinar last month, once workgroup topics are established, everybody is welcome to join the discussion in a workgroup of their choice.

One common viewpoint voiced is that we like the clear-cut, definite nature of a single numerical standard. Yes, we do indeed. We are proposing that there might not be only one clear-cut certification criteria, but a select few, all derived from a single target.

That target – the universal anchor, if you will — is not 15 kWh. It is actually 1 W/ft² peak load. It has been the basis of all things passive house since it was first scientifically defined in terms of an energy metric in the early 1970s. That’s when scientists and engineers in the United States and Canada collaborated to formulate a response to the oil embargo and the threat of energy dependence. This peak load principle was cemented then in the very first model energy code created in 1975 and it still remains in the IECC 2012 edition.

Today’s IECC commentary explains it very simply: If you have a room that is 100 ft² big, and that room has a 100 Watt light bulb in it, you are meeting your peak load requirement and don’t need a separate heating system.

This is a very simplified way to describe the conceptual target of passive house: If you can minimize your losses so that the internal heat gains match those losses, you can get rid of the heating system. Respectively for cooling, it works similarly: minimize gains through whatever measures and with it the need for cooling.

This ideal thermal balance is the underlying physics relationship of passive house. It’s what makes a building passive. This balance of gain and loss is theoretically possible and desirable anywhere. Can it be achieved anywhere for any type of building? That of course depends on the climate, the max delta T and the pocketbook.

There are climates where one would need infinite amounts of insulation if using affordable insulation (approx. R-4). Of course, if one works for NASA or can afford 6+ inches of vacuum insulation at an R per inch of 60, sure, we can built a passive house in the Arctic, what say I, on the moon!

In practice, the climate sweet spot for this principle is the relatively narrow belt of the “moderately cool climate.” This zone is heating dominated only. That means no complications having to optimize cooling and heating against each other; there is not too much sun, and humidity is not an issue. The balance of losses versus gains in this climate pencils out to almost exactly 1W/ft² peak load with an approximate insulation level of 12-14” for a well oriented, small, compact single family home and essentially no cooling needs.

Bingo! By using superinsulation, middle of the road Solar Heat Gain Coefficients, very good windows (the now well-known design recipe for components in this particular climate), we achieve an annual heating demand on average of 15 kWh/m²yr or 4.75 kBTU/ft²yr. No rocket science. Simple energy balancing.

15 kWh/m²yr or 4.75 kBTU/ft²yr are not part of the “functional definition” of a passive house; it is a consequence of applying the passive house peak load target and the related strategies in a climate where it works almost perfectly.

To summarize: the peak load target of 1W/ft ² is the anchoring principle, since 1975. It is a goal, one more practically reached in some climate zones than others. That’s why it’s become clear that the idea of refining the annual figure to climate zones will result in a tightening of the standard in some climate zones – not a relaxation, as some generally understood the proposal to do.

Climate variation make things a bit more complicated — but not that much. More on that in a future blog post.

Thanks for reading,

Kat

The Anchoring Passive House Principle: Equal In – Equal Out

We are glad that this topic of local climate-specific refinement of the passive house standard has sparked such a lively debate and discussion. Clearly there is a lot of interest in the topic! That’s really good.

I’d like to take this opportunity to explain why our proposal to make passive house accommodate North American climate variations does not challenge the standard’s core principle.

We consider the passive house standard’s anchoring principle to be its commitment to comfort through near-perfect balancing of losses and gains. To date, meeting this goal has required minimizing peak load (the worst case scenario of heat loss on the coldest day of the year) to approximately 1 W/ft².  At this peak load only a very small back-up space conditioning source is needed to keep comfortable.

The original idea of this balancing act — and of the peak load target of 1 W/ ft²  — pre-dates the European passive house standard by more than 20 years. The peak load target was first introduced in the U.S. inaugural model energy code in 1975 (a code created as a result of the oil embargo in 1973). Today’s IECC commentary explains the principle very simply: If you have a room that is 100 ft² in area, and that room has a 100 watt light bulb in it, you are meeting your peak load requirement and don’t need a separate heating system.

Of course this is a very simplified way to describe the conceptual anchor of passive house, the light bulb being a placeholder for the sum of the internal energy sources matching the losses through the envelope, including ventilation losses. Equal in – equal out.

Now let me explain why we do not consider the 15kWh metric as either a magic number or an anchoring principle, but rather as a derivative of that peak load assumption. The 15 kWh/m²yr (or 4.75 kBTU/ft²yr) annual heat demand metric is used to identify the amount of heating energy consumed over the period of one year.

That 15kWh figure was derived for the German climate from the peak load target figure (1 W/ft².). It so happens that Darmstadt, Germany is one of the climate sweet spots where limiting heat loss to that 1 W/ft² (10 W/m²) threshold is possible with relatively reasonable and cost-effective amounts of insulation. Germany’s climate is called “moderately cold” for a reason. The delta T is not that great. Heating is the only climate issue that needs to be addressed. That makes the design process — relatively speaking — easy and clear-cut as there are no additional conditions, such as cooling needs or dehumidification, to consider.

We know the design recipe components necessary for building a European passive home envelope that keeps heat loss smaller or equal to our internal gains, or, in other words, meets the 1 W/ft² (10 W/m²) peak load criterion: we calculate the required amount of superinsulation; we use high quality windows, we assume airtightness at 0.6 ACH50…

In Central Europe, we reach the 1 W/ft² (10 W/m²) peak load target with an approximate insulation level of 14 inches of R-4 for a well-oriented, compact single family home. A practical and attainable scenario — in Darmstadt.

From the specs for that same house, we can calculate the total energy usage for heating over the period of one year based on the climate-specific heating degree days. For the Darmstadt climate, that annual heating demand calculates to approximately 15 kWh/m²yr or 4.75 kBTU/ft²yr. No rocket science. Simple energy balancing.

Therefore we do not consider the annual heating demand (15 kWh/m²yr ) as a fixed and given part of the “functional definition” of a passive house,. It is a consequence of designing to meet the peak load criterion of 1 W/ft² (10 W/m²) in the particular Central European climate.

The 15 kWh figure is a good median starting point for passive designs, as it is derived in a median type climate — median delta T, median length of time when heating is required — where the peak load balancing act is fulfilled almost perfectly. But this is only one specific climate with one specific combination of climate characteristics. This 15 kWh criterion will need to flex as the delta T and amounts of heating degree days change and the underlying principles are applied in different, more extreme climates that deviate significantly from the median base line climate of Central Europe.

Aside from heating, the existing standard is limited even further when we factor in additional North American climate issues such as cooling and dehumidification.

To reiterate:

  • We consider the passive house standard’s anchoring principle to be its commitment to comfort through near-perfect balancing of losses and gains.
  • To date, meeting that balance has meant minimizing peak loads to approximately 1 W/ft².  In Central Europe, that happens to pencil out to the 15kwh average consumption figure.

But, we will demonstrate in a future blog post that achieving that peak load goal (and therefore the 15kWh max threshold figure) is next to impossible in some climates, and definitely not practical. Because the peak load of  1 W/ft² doesn’t apply everywhere, neither can the 15kWh.

Other building science experts, Including Marc Rosenbaum, agree that the current standard has limitations, and offer their own ideas about addressing the issue. (Check out Marc’s proposal for New England.) The good news is that despite all these reasonable challenges to the notion of a single standard, the design principles still hold true, and the peak load target remains a useful tool as a benchmark — even if not an absolute in every single climate zone.

As we develop the specifics of our proposal, we look forward to discussion and debate among all interested and knowledgeable parties. Combined with the growing body of data we’ve accumulated from passive house projects that have been built around the continent, we believe we can introduce the flexibility that will make fundamental passive house principles mainstream practice.

In the meantime, look for more on lessons learned, climate complexity and how to possibly refine annual heating and cooling demands while maintaining the underlying physics principles in upcoming blog posts. Stay tuned!!