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Policy Watch

It’s Either Net Zero or It’s Not

ASHRAE codifies evaluation standards for net-zero-energy and net-zero-carbon building performance

A certified home that meets the standardized definition for net-zero-energy performance, meaning the energy coming into the building is less than or equal to that leaving it during construction and operation. Photo credit: Janet Griswold Photography, Seattle, Washington

For developers, corporations, and even entire cities and nation states, meeting climate goals has been boiled down to a single contingency: achieving net-zero emissions. That now ubiquitous buzz phrase “net zero” has become the yardstick by which we measure our collective virtue and commitment to stemming the climate crisis, one CO2e at a time.

Along the journey to net-zero (or zero net) emissions–broadly speaking, ensuring any anthropogenic greenhouse gas emissions that are otherwise unavoidable get removed from the atmosphere through offsets or other means–are the prerequisite steps of neutralizing one’s reliance on non-renewable energy sources and, ultimately, counterbalancing all that operational carbon output. Maybe you commit to restoring native habitats through reforestation, or maybe you go all in on direct air capture and storage (DACS).

Whatever the means, trying to decipher what makes something legitimately zero net energy or zero net carbon can feel downright Sisyphean. The technical definition of a zero-energy building may be ironclad, but the practical definition (and means to achieving net zero) can vary, often wildly.

Thankfully, the common definitions now have a complementary standard. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has, for the first time, published a set of requirements, in the form of ASHRAE Standard 228, for evaluating whether a building meets the definition for zero net energy or zero net carbon. In the strictest terms, this means that the source energy or carbon flows coming into a building or site must be less than or equal to those flowing outward during building or site operations, or any allowed offsets. Standard 228 is, for all intents and purposes, perhaps the closest thing the building industry now has to a universal yardstick for determining whether a building is in fact as green and energy- and carbon-neutral as it claims to be.

“Any definition [of net zero] comes down to two things: boundary and metric,” says Paul Torcellini, principal engineer with the National Renewable Energy Laboratory (NREL) and vice-chair of the committee that wrote Standard 228. Torcellini, who also co-authored the U.S. Department of Energy’s “Definition Framework for Zero Net Energy,” in 2012, understands the nuances of calling something net zero and all that entails. “When we originally did this 15 years ago, people wanted it based on site energy, which is easy to measure. Then some people wanted it to be source energy, which gave us a little better handle on the balance between some of the scope 1 [emissions] and the inefficiencies of delivering electricity.”

Standard 228’s calculations are based not on site energy, which is limited to everything consumed and emitted within a site’s boundary, but on a building’s source energy, comprising a far more holistic set of variables. Source energy is defined as the site energy plus the estimated energy consumed or lost in the extraction, processing, and transportation of primary energy forms (e.g., coal, oil, natural gas, biomass, etc.); energy consumed when converting to electricity; and energy consumed or lost during transmission to the site.

In a world gone crazy with greenwashing, it’s refreshing to have at least one sustainability benchmark laid out in black and white. “You’re either net zero or you’re not. It’s pass or fail,” Torcellini says. Granted, although the new standard accounts only for operational emissions, Standard 228’s committee was evidently intent on accounting for as much energy and carbon dioxide equivalents being used, distributed, emitted, and lost as possible, within reason.

As expected with any standard or program aiming to set the dial to zero, certain allowances are in place, particularly for buildings or sites that lack “the opportunity” to tap into on-site renewable energy sources. The purchase of carbon offsets and renewable energy certificates are options, as is off-site renewable energy procurement. One of the biggest allowances, however, doesn’t concern offsets or other market-based instruments, but regional considerations.

The means for reducing emissions varies depending on where it’s taking place. And whoever happens to hold jurisdictional sway in a particular region can adjust emissions factors, for better or worse. (ASHRAE 228 specifies 19 subregions in the U.S. alone, with varying benchmarks for CO2 emission intensity levels.) According to Torcellini, “There are provisions [in 228] that if the authority having jurisdiction wants to pick some other set of emissions factors, if they’ve got some other utility mix, or they’re generating their own [energy], they can come up with their own factors and write in those numbers and say, ‘This is now law of the land.’”

Torcellini cautions that ASHRAE Standard 228 doesn’t represent code or policy. “It’s a standard. ASHRAE provides the mechanism, but somebody else needs to determine if you meet the criteria. It doesn’t specify how to measure or report quantities.” For that, the new standard draws from ASHRAE 105, which outlines “a commonality in determining and reporting the energy-related performance of buildings.” Torcellini calls 105 a “methodology for collecting relevant data.” So, if 105 tells you what to measure, then 228 is the ruler.

In some sense, abiding by a performance standard without the benefit of a building certification program like LEED can seem like an empty gesture in reverse–action was taken, but without public knowledge, that action’s value is minimized. Of course, progressive building codes and climate policy don’t materialize out of pure sentiment. They are the products of consensus, formed by committees, composed of building professionals and energy performance experts who spend years hashing out the finer points of what’s required of high-performance buildings. “Standards are designed to become policy,” Torcellini says. Let’s hope ASHRAE 228 isn’t the exception.


Justin R. Wolf is a Maine-based writer who covers green building trends and energy policy.





  1. Expert Member
    ARMANDO COBO | | #1

    I don’t know if idealistic pencil pushers are aware of the realities for the renewable industry, or at least in solar PV systems when it comes to net metering. Net metering rules are not codified nor regulated at a national scale. In many areas in America are nonexistent and in many others are lopsided to producers, distributors and retailers.
    According to the Energy Information Administration (EIA), losses in generation, transmission, and distribution can be up to 34%, and I believe, until a fair policy change is made available at the national level, it's unfair to “move the goal post” for homeowners to become “net-zero” by having to account for production and transmission losses.
    If homeowners are required to add an additional 34% to the PV system, basically it erodes completely the IRA tax credits.

    1. GBA Editor
      Justin R. Wolf | | #3

      I agree. Although in practice the new standard applies to all buildings, the subtext suggests it be applied to large commercial and residential construction, retrofits, etc. Also, I can't see too many homeowners electing to use 228. I've received some feedback that ASHRAE has finally caught up with Passive House (30 yrs late), but I'm not sure the comparison is apt. The International Passive House standard is codified, whereas Standard 228 is malleable depending on climate zone/subregion, regional/local codes, and other jurisdictional concerns. Net-metering regulations and credits should also apply when using 228, and most states (33 last I counted) do mandate credits in some form, although how they're applied across the board is scattershot at best, leaving the question: should there be a national policy? For large buildings? Yes! But on the topic of private homes, I have trouble seeing a future where achieving net zero performance of any kind is anything but voluntary.

    2. StephenSheehy | | #5

      Whether rooftop solar loses anything significant in transmission or distribution is an interesting question. My house uses the electricity my solar array produces when we are using electricity, with any excess going into the grid. My understanding is that the electricity my array sends to the grid is used locally, by my neighbors. Put differently, if my little town had it's own grid, all of my excess would stay here. So the typical losses in transmission from a power plant to my house are irrelevant if we're trying to see if I'm net zero.
      Of course, even if over the course of a year we generate as much as we use, that doesn't mean we're not dependent on the grid.
      And if net zero is hard to define, how about "net zero ready?"

      1. DavidJones | | #6

        Zero Energy Ready Homes happens to be the name of an existing Department of Energy program. (A step up in performance from Energy Star). ZERH isn't not Net Zero by pretty much any definition.

  2. Danan_S | | #2

    It sounds like Section 228 can be used to calculate net zero status for existing high performance homes, or like Passive House is it only applicable to in process builds or retrofits?

    1. GBA Editor
      Justin R. Wolf | | #4

      The calculating is left to third party certification programs and the like. But yes, 228 can be applied to existing buildings, new builds, retrofits, etc. Specific performance metrics are built into Passive House. Not the case with 228.

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