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.
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