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Photo courtesy of Solid Green Systems

Zero Energy Homes: Built Projects & Programs Chart the Road to Adoption

By Ann V. Edminster

Note: Apologies to readers who may not be familiar with all the acronyms contained herein; in deference to the more acronym-savvy among you (most of the building industry), I’ve omitted them to streamline the reading! All may be decoded readily online.

When the Net Zero Energy Coalition set out to inventory the zero-energy (plus/minus) homes in the US and Canada, we had questions – that was the whole point, after all. We wanted to create a picture of the state of the zero-energy residential construction movement by asking some things that we didn’t know, such as How many zero-energy homes are there, anyway? The basic results of that inquiry are quite interesting, and are well-covered in our January 2016 report, To Zero and Beyond: Zero Energy Residential Buildings Study, and summarized in this nifty infographic.

I also expected that we would find out some things about the ZE homes themselves. We did, and those findings, albeit less surprising, are also helpful inasmuch as many ZE builders and designers from across North America have validated one another’s experiences. What I didn’t anticipate was what we would learn about the organizations and programs involved in the ZE arena, and what their similarities and differences would illuminate. What follows is a brief summary of key findings about the homes and then a short discussion about the ZE organizations and programs.

The ZE Homes and Those Who Create Them

We learned that most ZE residential projects – as documented by their designers and builders (via case studies and personal communications) – feature several common elements. At the top of that list are optimized building geometry, along with high-performance enclosures and HVAC, and of course renewable energy systems (except for those that are zero-energy ready). Other common aspects include a focus on embedded systems (e.g., advanced framing, efficient electrical and plumbing layouts, etc.), optimized hot water systems, best-in-class appliances and lighting, and performance dashboards.

Certain design considerations emerged as critical to success on ZE projects. Chief among these was mechanical product selection, low-capacity HVAC equipment and ERVs in particular. Continuing the equipment theme, many ZE designers and builders also noted challenges related to water heating – electric heat pumps are favored, but that choice can be inhibited by space constraints and by codes and utility rate structures that favor natural gas. Other noteworthy design issues include the need to fine-tune enclosure specifications and details to optimize performance, and the importance of a regionally appropriate and attractive design.

Two closely related construction themes were highlighted: a good team and good coordination across the team are absolutely essential; as is active quality management, including rigorous onsite verification of performance.

Another category of findings related to innovation. ZE designers and builders clearly revel in experimentation, tinkering with their designs and details to arrive at elegant, cost-effective solutions. They are also a highly collaborative lot, frequently citing the need for close work among the design team, suppliers, manufacturers, public agencies, and trades. And finally, these industry leaders are also teachers – many are actively engaged in advancing knowledge of ZE practices by sharing their experiences with others, both formally and informally.

The ZE Organizations and Programs

In order to assemble the inventory, we called upon many allied ZE stakeholder organizations (listed in our 2016 report) to do outreach to their constituencies via website, newsletters, and direct email. And in order to parse the data (in both the inventory and the case study database, evolved in close collaboration with its originating organization, the Northeast Sustainable Energy Association) to be of greatest utility to those stakeholder organizations, we worked with them to identify their information needs and the way(s) each of them approaches the definition and/or categorization of “zero net energy.”

We found two key distinctions among the various programs (labels, ratings, certifications, criteria, etc.). First, some rely upon modeling from energy simulations as the basis for the determination of a project’s zero energy status while others required documented operating energy data (typically, a year’s worth of utility bills). The second area of distinction was the types of renewable energy sources that may be used in meeting ZE (plus/minus). For inquiring minds, these divergences raise the question, Why be different?

Only two organizations – International Living Future Institute (ILFI) and Thousand Home Challenge (THC) – require operating energy documentation in order to legitimize their claims to having achieved zero net (or net positive) energy.  All the others rely on modeled energy performance. So, why? The rationale for requiring operating energy data is that it’s the only way to know if ZE has truly been achieved. Fair enough. But in favor of modeled energy performance is the argument that it’s the only objective way to evaluate the home without occupant behaviors muddying the waters. Also fair. So – at least as far as I’m concerned – there are good reasons for both approaches.

When it comes to allowable sources, all programs allow the use of renewable energy produced onsite; where they differ is their views on the use of offsite sources. The US DOE and Passive House International are the only programs that unequivocally allow use of offsite sources. All the others limit the use to onsite energy or introduce qualifiers of one sort or another to the use of offsite sources:

ILFI –  only per “scale jumping” criteria, generally nearby; and no renewable energy credits (RECs)

Earth Advantage – neighborhood/community-based sources under consideration

Passive House Institute US – neighborhood/community-based sources

THC – only if the owner/occupant owns a share of the system and has actual production from the facility

A single concern underlies all these varied caveats: we don’t have a reliable means of assuring that offsite sources are truly serving the projects in question. This is an accounting and chain-of-custody problem: if the renewable energy system isn’t physically attached to the project, how can its production be unequivocally – and uniquely – attributed to a specific project? At present, it can’t. RECs have a number of limitations and are only traded on the wholesale market.

This suggests an important issue for the ZE community, and an opportunity to join forces to create a robust mechanism for renewable energy accounting across project boundaries. There is a strong rationale for doing this, as the solar (or wind) resource may be better down the street, across town, or in the next county; and pooled renewable energy facilities offer economies of scale that can’t often be matched on a single project.

In conclusion, yes, diversity is healthy, and there is a place in the ZE ecosystem for both modeled and measured energy performance. But unity is also important to the growth of the ZE movement, and I hope to see the ZE community rally behind the development of a solid renewable energy accounting mechanism.

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This article presents an abbreviated discussion of the topics covered in the paper of the same title written for the ACEEE 2016 Summer Study on Buildings.

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