ASHRAE 227 Passive Building Standard Released for Public Comment

As you might know, a committee has been working for more than four years to codify the ideas of passive building into a standard written in code-intended language. The objective is to facilitate “making passive house code” by writing a passive building standard that could be adopted by reference directly into law, and thereby maximize its overall energy-saving impact on society. 

This has been going on under the auspices of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), which follows American National Standards Institute (ANSI) consensus processes and can confer ANSI approval on its standards. For most jurisdictions in the US, ANSI approval is a requirement to adopt a standard as mandatory. There are already jurisdictions interested in adopting a passive building code. 

The committee has been working since June 2019, and has very good news this week: the ASHRAE Standard 227 - Passive Building Design, is now out for public comment, through Nov. 13, 2023. 

NOTE: Before these standards are finalized, they must go through a series of public review periods. This first round is an Advisory public review. The review draft is the complete document, but “Advisory” means the written comments do not need to be formally responded to by the committee. The plan is to invite commenters to the appropriate working group meetings (I am chair of one). Later, the standard will go out for a more formal Publication Public Review.

The official Purpose Statement of ASHRAE Standard 227 is: “This standard provides requirements for the design of buildings that have exceptionally low energy usage and that are durable, resilient, comfortable, and healthy.” The Scope Statement goes on to include design, construction, and plans for operation.

The scope of the draft standard encompasses all types of buildings, but some of its provisions only apply in certain situations, e.g., to single-family detached, or where all heating/cooling equipment runs on single-phase electric power. There is not just one demarcation line that defines the requirements e.g. “low-rise residential” and “other than low-rise residential.” (I’ve been resisting limiting the scope or breaking it arbitrarily into residential and commercial).

What’s been done here is an effort to make the concepts and techniques of passive building shine through a different structure for compliance, verification, administration and enforcement – a structure that works more like other energy codes and less like proprietary certification programs (of Phius and PHI). The key concepts and techniques have all been addressed. This includes: minimizing heating and cooling loads with passive measures, minimizing energy use overall, air-sealing, insulating without thermal bridges and without incurring moisture risk, and managing solar gains. But, compliance works differently. 

You may have noticed that we’ve been making Phius’ absolute energy performance targets more nuanced with every cycle since 2015. ASHRAE 227 takes this to the logical conclusion where the performance targets are project-specific and determined by the performance of a more prescriptive baseline case, as with the International Energy Conservation Code (IECC) for example – and that more prescriptive case is also a compliance path. This approach has the notable advantage of being able to cover a wide variety of nonresidential and mixed-use building types without requiring a custom target-setting study. (As I’ve opined before, it's not a mystery what factors contribute to high heating and cooling loads, and therefore it should be possible to regulate those one by one: infiltration, heat transmission, solar gains, internal gains.) 

One of the main points of tension on the committee has been about how prescriptive to make the prescriptive path, and how available it should be. The advantage of prescriptive rules is they are straightforward to apply and to verify. Their disadvantage is inflexibility, and if a designer finds any one of them irksome, they are forced onto the performance path and required to do energy modeling. The advantage of the performance path is flexibility and its disadvantage is the greater skill and effort needed for the modeling, and for verifying the modeling.

What we have right now is a (we think) clever compromise whereby most of the “prescriptive” requirements are actually “subsystem performance” requirements. This means they allow trade-offs within a limited scope, and require some calculation of a metric, but short of whole-building energy modeling. For example: the heat transmission loss is regulated by limiting the overall “U*A” conductance of the envelope, but does not go so far as to tabulate U-factors for walls and roofs separately. The more “performance-y” the requirement, the more one has to write in the standard about how to calculate the performance metric, creating a need/opportunity for providing calculation support software. Some members would have no qualms about requiring most projects to do whole-building energy modeling and others would like an even more prescriptive path and/or one that is available to more types of systems. 

There are also requirements that apply to both the prescriptive / subsystem-performance path and the overall performance tradeoff – these sections are to ensure that durability, health, and comfort are not compromised in the pursuit of exceptional energy performance, and that construction quality is assured.

There hasn’t been a lot of testing of the proposed rules on sample buildings, because some of the subsystem performance metrics aren’t directly supported by current software. The protocol should be clear but at present it’s a bit awkward to set up the required “side calculations.” The committee could learn a lot from people trying to test the rules. 

Please read it, try it, and comment!

Another aspect of proprietary “green building” programs to consider is the requirement of their proprietary credentialed professionals, or certified products. This can’t be done in a code-intended standard – it must confine itself to requiring skills, and give the authority having jurisdiction (AHJ) a lot of discretion regarding qualifications of individuals, and to some extent what constitutes valid product rating data.

The 227 project started with a “clean sheet” and every existing energy code, standard, or proprietary program has been regarded as “previous work” to be considered and built upon. As an ASHRAE standard project, it is obliged not to conflict with other ASHRAE standards. We believe it will contribute strongly to ASHRAE’s position on decarbonization, in the areas of energy efficiency and operational GHG emissions, and also addresses refrigerant emissions and renewables.