Climate-Specific Passive Building Standard
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.
- Please download the final draft report from the study here.
- 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 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.
- Members must submit formal comment to ensure Tech Committee review.
- Comments from the general public are open on the Klingenblog.
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.
Moving away from a one size-fits-all approach to a climate specific standard promises to make passive house more cost-effective, and to dramatically accelerate adoption.
PHIUS and Passive House Alliance US are honored to be part of the tradition of passive house. Though it traces its roots to the North American super-insulated building movement of the 70s and 80s, the locus of the effort moved to Germany in the early 90s and evolved there into the standard we know today, with its three metrics, modeling approach, and training regime.
We are committed to its principles of low-energy building design, resilient construction, and comfortable, healthy living. But the specifics of the codified standard developed in a unique climate, economy, and culture: Germany. In the interceding years we’ve seen the standard adapted by different means, measures, and modifications in other countries and regions. In the even more heterogeneous climates of North America the standard needs to evolve to respond.
The current standard’s requirements for space conditioning do not fit the diversity of North America. While they apply well to a central European context, they are too lax for some of our continent’s climatological/economic zones and too punitive for others. The implementation of the standard across North America bears witness to occasional unsatisfactory results: comfort issues, performance issues, and unjustifiably expensive envelope specifications. This limits meaningful adoption of passive house across anything but the middle of the spectrum.
It has become clear that these cost-optimization, comfort, and performance issues arise from a rigid attempt to apply the old standard to new conditions. The standard must adapt to this climatological complexity or risk obsolescence.
One of the greatest strengths of the Passivhaus standard is that it is built on the scientific tradition. In the words of Thomas Kuhn, “scientific knowledge is cumulative, building on previous benchmarks to scale new peaks.” The Passivhaus standard was set in Germany as a function of the observables there, which were determined by local conditions and by the tools used to observe them. North America is different, because it is a new environment and because our models are more sophisticated, generating new and more accurate reams of data. Therefore it is imperative that we “scale new peaks” with the standard by providing a more granular, more accurate overlay to the climatological and economic landscapes of North America.
The proposed standard adaptation carries passive house toward greater implementation, scope, and intensity in North America.
The PHIUS Technical Committee, led by Senior Scientist Graham Wright, undertook the adaptation with a deep respect for the work that had been done before by countless others. That respect was matched by intense rigor in developing new guidelines.
The tremendous technical effort necessary to create this first adaptation points to even more work in the future. While this is a sobering thought, there is power in this realization. The revolution is the recognition that the way we think about buildings has changed in accordance with the new tools we have to examine them. If we are true to the scientific method and our past experience, this process will never end.
PHAUS Member and Founding President of the Passive House Alliance U.S.
What Will Be Different?
The proposed adjusted standard has the same high-level organization as before. Adaptations are proposed for all three main pillars.
- The air-tightness requirement was reconsidered on the basis of avoiding moisture and mold risk, using dynamic hygrothermal simulations to be published elsewhere. The proposed change is from a limit of 0.6 ACH50 to 0.05 CFM50 per square foot of gross envelope area. This allows the airtightness requirement to scale appropriately based on building size. Before, a larger building that met the 0.6 ACH50 requirement could be in actuality up to seven times more leaky than a small single family home that tested the same.
- The source energy limit was reconsidered on the basis of the global CO2 emission budget. The following changes are proposed to make the scoring more fair and the calculation more accurate:
- Change to a per-person limit rather than per square foot of floor area, at least for residential projects. This follows the fair share principle and removes the penalty for those who seek to reduce their carbon footprint by building small homes.
- Increase the source energy factor for grid electricity from 2.7 to 3.1, consistent with the US national average according to NREL data.
- Increase the lighting and miscellaneous plug load defaults to 80% of the RESNET defaults to better reflect actual US usage, and make the internal heat gain calculations consistent with those assumptions.
- To absorb the “shock” of the large increase in lighting and plug load defaults, temporarily relieve the source energy limit to 6000 kWh per person per year, tightening to 4200 again within a few years TBD.
- Apply the limit to: the source energy calculated net of the estimated fraction of onsite PV or other renewable electricity generation that is used onsite as it is produced. This puts PV on a similar footing to how solar hot water is currently treated. (For a typical residence, most of the output of a 2 kW PV array would “count”, depending on the climate.)
- The space conditioning criteria were reconsidered on the basis of economic feasibility. The proposed change is to
- Shift to mandatory, climate-specific thresholds on specific annual heating and cooling demands and peak heating and cooling loads, which are set at cost optimal “sweet spot” slightly beyond BEopt’s cost optimum for project’s actual climate for increased resilience benefits. This ensures efficiency measures will have reasonable payback relative to operational energy savings. The peak load thresholds may be adjusted to ensure hourly comfort or the ability of the home to thermally coast through power outages.
- Simplify the reference floor area from TFA to an inclusive interior-dimension floor area.
By its structure, the proposed standard also retains the feature of the “three hurdles to net zero.” The designer’s attention is directed first to reducing heating and cooling energy use by passive means (including some mechanical devices,) then to reducing total energy demand by efficient equipment (and some renewables,) and finally to net zero by more renewable generation.