Feedback on the standard adaption: A summary

GWLast year the PHIUS Technical Committee published its draft report on a climate specific passive building standard. It also called for formal public comment. Here, with an update on that process, is PHIUS Senior Scientist Graham Wright.

We got some good feedback on our standard-adaptation work – fourteen folks submitted some fifty pages of formal commentary altogether. Thanks to all who took the time to write out their thoughts. The PHIUS Technical Committee (TC) reviewed all the feedback.

I’ll summarize the process, but first you might remember that our report is also a report to U.S. Department of Energy Building America (BA) program, a proposal for the next-generation Zero Energy Ready program (ZERH). The reviewers for BA sent 134 line-item comments on the draft report. (We’ve been busy responding to those, and we think the final report is much better now!)

Click on the cover graphic to download the final U.S. DOE Building America report at the Building Science Corporation site.

The DOE/BA and the passive house community have the same goals and are, at a broad conceptual level, working on the same thing (otherwise this work would not have been funded.)  At the workaday level though, there are a lot of differences, and also a lot of investment by the two communities in their own approaches – it’s part-and-parcel with the commitment and passion for better building that both communities share.  But when you ask the questions “is there anything passive house can bring to BA/ZERH” and “is there anything BA can bring to passive building,” it turns out the answer is yes.

The TC believes we’ve achieved a fruitful synthesis, a best-of-both-worlds combination. For example, when it comes to designing for high performance, we agree it’s better to set performance targets and do an energy design than to use prescriptive tables (and by the way that design can be somewhat site-specific). But when it comes to field quality assurance, then  a checklist table – like the BA approach — is the right tool for the job.

To put a finer point on it, we at PHIUS hope the final report persuades BA that the ZERH program should be a performance standard, with criteria on both heating/cooling loads and on total source energy, and that those performance targets are predicated on ducts inside, strict air-tightness, and using really good windows for comfort reasons.

Likewise we hope it makes the case to the passive building community that the heating/cooling criteria can be adjusted for economic feasibility / competitiveness in a climate-sensitive way, that the risks to comfort and building durability are low, and that the heating/cooling energy savings are still impressively deep.  Over all the climate locations studied, the proposed criteria represent median reductions in peak heat load of ~77%, annual heating of ~86%, peak cooling of ~69%, and annual cooling of ~46%.  (The baseline is 2009 IECC code.)

So, about those formal comments: Most commenters checked either 12-20 or 20+ years experience. In terms of survey questions we asked, no one liked star-ratings, so pass-fail it is. In going through the feedback the TC found no surprises–most all of the concerns had indeed been fully vetted en route a consensus over the past two+ years.  Here are some of the specific questions we received, along with answers:

Q: Could WP software be modified to make heating/cooling load calculations consistent with ACCA Manual J and ANSI/ASHRAE/ACCA Standard 183?
A: That is possible!  Added to the feature request list.

Q: Could PHIUS consider consolidating QA/QC checklist to be free standing from DOE ZERH and EPA Energy Star (for both residential and commercial projects)?
A: Some progress has been made on this. Stay tuned.

Q: Will the standard help me design smaller passive houses?
A: The short answer is probably yes.  There is no explicit “small house break” but there are three changes that indirectly tend to benefit small detached buildings at least in some climates:  air-tightness criterion by shell area instead of volume, source energy allowance per person instead of per square foot, and higher plug load defaults and detailed internal-gain accounting.

Q: Has there been any progress with PHIUS and NFRC in aligning data to meet PHIUS needs and possibly using NFRC data?
A: Not a lot. But we want to get it done this year. Third quarter.

Q: Please explain why you chose the specific denominators in the formulas. For example, why $ 0.155 electricity? 482 kWh? 1341 HDD65?
A: Those are the best-fit numbers determined by the regression analysis, that is, it’s like when you fit a line to a trend in x,y data, the trendline formula has the form y = m*x + b.  The numbers in the denominator are like the m, the slope or sensitivity to each of the factors.

In terms of final refinements to the new standard, PHIUS has been operating an alternate certification path along the lines of the BA draft report for some months as a pilot program. In the February and March meetings, the TC did pass some changes in advance of broader implementation. The changes came from both the feedback and the pilot program experience.

One kind of comment that spoke to us was, “this isn’t disruptive but you might want to change this to align with, or not conflict with, the building code.” The most to-the-point answer to feedback about rules is what gets changed or upheld, so here is the list of changes the TC agreed on:

  • Source energy: The U.S. source energy factor for electricity is adjusted to 3.16 (aligns with IECC 2015). The residential source energy limit is adjusted to 6200 kWh/person.yr.
  • Air-tightness criterion: 0.05 cfm50/sf of envelope area or 0.08 cfm75/sf (testing at 75 Pa aligns with commercial code and U.S. Army Corps). If testing at 75 Pa, report the flow coefficient and exponent from the blower door tests (that way the software can extrapolate to 50 Pa for compatibility of figuring the natural air change rate for infiltration losses).
  • Non-threatening air leakage: If the air-tightness criterion is missed, and the extra leakage can be proven to be due to a non-assembly-threatening leakage element such as a vent damper, certification staff may allow that element to be taped off for the purpose of passing the air-tightness criterion. The un-taped test result must be used for the energy model.
  • Phase-in period:  Dual certification path continues until September 15, after that the old protocol is phased out for PHIUS+ 2015.
  • Break-in period: If a project is seriously constrained on one of the criteria, a case-by-case overage may be allowed on any one of the four space conditioning criteria, or source energy, for the next year.
  • Retrofit:  The retrofit criteria are the same as new construction, except for a case-by-case energy allowance for foundation perimeter thermal bridges or other such hard-to-fix structural thermal bridges. Provided the design is “damage-free” that is, low risk from a moisture point of view.
  • Add-on badge: for supply air heating and cooling sufficient, per static calculation, with the average ventilation rate no more than 0.3-0.4 air changes per hour. (That is, low peak heating load and low peak cooling load. Special recognition for those who favor and design to this particular “functional definition” of a passive building.)

And finally, Katrin’s long-awaited favorite:

  • Add-on badge: for source net zero.  Onsite renewable electricity generation above any that was already credited as coincident-production-and-use, counts towards net zero with the same source energy factor multiplier for electricity, i.e., 3.16.

To me the most substantial comment was along the lines that cost has been added on to the building delivery process, when you consider the labor of the CPHC, the pre-certification review, and the rater visits for quality assurance. The TC believes much of this concern is simply a matter of getting used to the requirements until it becomes the new normal, but we know that there is room for improvement on making the planning tools easier to use, and we will keep working hard on that.  Most commenters felt it was also very important to get the standard written out in human-readable form, not just encoded in WUFI Passive, and we will work on this as well.

Overall, we believe that PHIUS+ 2015 will make passive building more cost-effective across climate zones. The community’s collective experience informed all the work–so thank you all for all your input and hard work and again, thanks to everyone who took the time to submit formal comment. We’re excited to implement the new standard and believe it will dramatically increase adoption of passive building.


Notes from the Frankfurt Conference

The impetus for my journey to Frankfurt, Germany in April was the 17th International Passive House Conference. As I walked toward the venue it occurred to me that this is my 10th anniversary at that event…

…and that we’ve come a long way on this side of the pond. It looks like we might be able to match participation this year at our upcoming 8th Annual North American Passive House conference in Pittsburgh. Overall participation in Frankfurt, according to the distributed participants list, was 650 people.


Ninety exhibitors were on the exhibit floor. Among those were quite a few very large companies such as Saint-Gobain and Sto, who have embraced passive building solutions. One company struck me as especially interesting for the U.S. market: Compacfoam. They offer very simple thermally broken solutions using their compressed and structurally stable foam product. Those work for window installation, thermally broken point connections of curtain wall facades, point connections for balconies or porches attached back to the house structure as well as for the insulation of window frames. Those solutions could easily be implemented in the United States. All we need is the material.

Overall on the trade show floor, the innovations seemed to have leveled off some. In many cases the innovations presented were refinements of an already existing product. This is rather good news as it signals that passive in Europe has truly become mainstream. The smaller numbers of participants and exhibitors at the conference can be explained that way as well: other larger more general building conferences have absorbed the topic and are offering equally qualified information. Passive building is everywhere!

Some significant updates from the passive building modeling front:  This year, only one year after the last 2012 PHPP update came out, a new 2013 PHPP version has been published. Word is that the PHI significantly improved the cooling demand and latent load algorithms to be more appropriate for hot and humid climates. A new latent demand annual budget had already been included in the overall cooling demand certification criterion for 2012.

Newly unveiled to the European market (it was released earlier here in the States) at the conference: WUFI Passive developed by Fraunhofer IBP. The new passive modeling tool — that in addition to just a static calculation method also includes hourly dynamic simulation capability and hygrothermal assessment — was presented to the worldwide passive building community. Overall it was good to see that everybody in the field is working diligently on passive modeling tools that are accurate for all climates including the more challenging hot and humid ones.

Back to the PHPP update: be aware that if you still use the older versions of PHPP (2007 through 2012) for your passive designs, it is very likely that your results may not be as accurate as they could be. You should consider upgrading. If you are working in more complex and challenging climates (very cold climate zones starting at 8 as well as mixed humid, hot humid, hot and dry climate zones, plus  all zones with very high solar radiation) PHIUS very strongly recommends to use a dynamic model in addition to PHPP (or to use WUFI Passive which does both calculations — passive static verification and dynamic modeling).

Some caveats: The stated improvements/changes in the algorithms in PHPP 2013 are a great step – it marks an acknowledgement that cooling latent issues were indeed not properly addressed until now. But, these changes for cooling and latent have not yet been verified in the various North American climates. Moreover, with more built examples and data now available, the larger question is: How accurate can a limited static representation relying only on monthly climate data really be? It is very likely that it does not afford enough granularity to accurately predict very complex interactions of buildings with a multitude of climate factors.

For those more complex climates with heating, cooling, latent and solar climate factor combinations dynamic modeling appears to be quite a bit more accurate, allowing designers and consultants to limit the inherent risks in modeling: under or over-predicting performance as well as verifying that comfort conditions are assured throughout all rooms and spaces.

PHIUS is not alone with this recommendation of combining a dynamic model with a simplified static one for the best results. Belgium, the country that recently made the news with its decision to make Passive Standards code by 2015 for all new and retrofit construction projects, also requires all designers to back up the static passive house model with an additional dynamic model! Hence, the Belgian representatives of the Plate-forme Maison Passive I met with in Frankfurt were very interested and excited to learn about the advent of WUFI Passive.

























Climate Data—When to Request a Custom Dataset

Ryan Abendroth–CPHC and former Certification Manager at PHIUS–with guidance on Abendroth, headshotselecting datasets for passive modeling.

CPHCs should use the guidelines below to determine which dataset will most accurately represent their current project’s location. Generally, for most projects, one of the existing downloadable datasets will be accurate and appropriate for use with WUFI Passive or the PHPP. In some cases, though, a project will require a more refined dataset customized to a very granular level in terms of location and conditions.

–To start, avoid using data for a location more than fifty linear miles from your project location.

It’s worth noting that even projects within this range may–in some cases–benefit from custom generated data. This is especially true if there are microclimate issues or impacts from geographical features including altitude changes between the project site and the weather station. (Site elevation is a modifier on the climate page in the PHPP that is often overlooked.)

–We recommend using a different/custom dataset if the difference in elevation between the project site and station location is greater than 300-400 feet.

The climate modifier in the PHPP adjusts the data by taking every 1000 feet of elevation change and adjusting it by 3.6 degrees Fahrenheit. We have seen very large discrepancies due to this adjustment because often times, the real world conditions for high elevation changes consist of microclimate situations that are difficult for the linear scaling of the modifier to accurately reflect. If there is not a station location within 300-400 feet of the project site, check for local data. The elevation modifier can also be used to adjust a data set to be in line with local data sources. This is helpful in cases where there may not be a Typical Meteorological Year (TMY3) station for more than 50 miles, or there may be microclimate effects that occur at a given project location that are not able to be accounted for in the base data set. By using the modifier, a dataset can be adjusted up or down to account for the difference in temperatures between the generated data set and local, measured values.

Why accurate data is critical

Having exact sets generated for data points nearest to the project is important because in passive buildings, we are reducing the energy loads so dramatically. Small changes (say 1 degree) in the average temperature throughout the year can have dramatic effects. For a 2000 sq. ft. treated floor area (TFA) building in San Francisco that was meeting passive house criteria, the difference was ~15% for the Annual Heat Demand. This is especially important when considering all of the factors mentioned above. For one project location, I gathered data directly from the station point and then generated a second set based on interpolation through Meteonorm to the exact same coordinates of the station. The result was a variance of +/- 4 degrees Fahrenheit as compared to the base non-interpolated values which equated to ~25%+ difference in Annual Heat Demand in that particular project.

Nothing changed about the location, just the method of generation that was utilized (straight derivation or interpolation). This is the basis behind my insistence on using TMY3 station points whenever possible.

News in the world of Climate File Generation:

The iPHA recently published a tool to generate climate data files for locations where none yet exist. It is an excellent attempt but the fine print recommends use for design only—not certification. This is because the granularity of the tool is only 75 miles by 75 miles, a resolution not small enough for most locations in the United States. It may be relatively accurate in the central plains, but once major geographical features come into play, the microclimate effects will make the iPHA tool only a rough estimate (which reflects the stipulation to use it as a design tool only) due to the spatial resolution being roughly 1 degree about the equator with some data being even less precise (referenced in page 321 of the 16th International Passive House Conference 2012 – Conference Proceedings).


Frequently asked questions:

Is the Climate Data robust enough?

Yes. The passive house verification in WUFI Passive and in PHPP allow architects/designers to design buildings based on two methods, either annual or monthly. The monthly method is the one you want to use for a variety of reasons (more on this later). Because of this, the climate data has been set up to not require very small increments or time steps in the calculation. The actual data sets are a representation of the hourly data from TMY3 sets. It has just been broken down into month-by-month averages instead of a large drawn out set with values every 15 minute or every hour.

What about more exact time steps or hourly values?

If greater specificity is needed in terms of time steps a different program should be used that has dynamic calculation capabilities instead of a standard static model. In many cases, this is not necessary as the passive house verification in WUFI Passive (and PHPP) has been set up to simulate dynamic modeling for passive house buildings. This is made possible because the short term fluctuations should matter less as the lag effect due to super insulation, air-tightness, and thermal mass, provides a buffer against isolated peak conditions.

This past May, the average monthly temperature was 73.2 degrees F, but the PHPP has the temperature as 64.2 degrees F?

Prolonged peak conditions have a large effect in terms of real world performance. However, there is a real difference between weather and climate. The climate is a an average of many years, while the weather is what occurs at any given time.  Climate data is unable to predict any given trend in the future weather. Next year, the monthly average for may could be 55F and even out this year’s unseasonable warm spell.

What about climate change? Should we make data for the future?

This is inherently difficult to predict. While many places represent a trend that is most likely warming, there are others where opposite phenomena could occur. Also changing could be the amount of rain, and the corresponding changes in radiation associated with an increase or decrease in cloud cover. Therefore, we should use the data that is available for our area and worry about updating it when new data comes out, but not worry about trying to predict the future.

What about humidity?

Humidity can be determined through the dew point temperature and average temperature within the climate data set.  As mentioned earlier, this is a monthly value and not as specific as may be needed for some modeling methods, but should be fine in most climates (more on this from future PHIUS Technical Committee articles).

Where can I see the most up to date list of available data sets?

All 1000+ climate data sets which have already been generated by PHIUS are available to download for PHAUS Professional level members at no charge. All existing climate data sets are shown on this map.

If I need a set generated, how does that work?

First, check the map linked to above to make sure that a suitable climate data set does not already exist for your location. A “custom” data set means that we will generate a new climate data set for you if one does not already exist. If this is the case, inquire with to determine the suitability of a site or to have a custom data set generated.

What does a custom generated dataset cost?

Custom data sets cost $75 for everyone, including PHAUS Members and non-members.

Email for more information about custom data sets.