Defining net zero energy

ASHRAE has a goal: net zero energy for all new buildings by 2030. What do engineers need to know to achieve this goal on their projects? How can the various engineered systems within a nonresidential building be integrated to achieve this goal?


The definition of net zero energy buildings (NZEB), also known as zero-net energy (ZNE), has been debated by countless stakeholders around the country. From coast to coast, engineers, architects, state agencies, and others have been trying to define what ZNE actually means. Source? Site? Building? Campus?

In Massachusetts, the 2009 report “Getting to Zero: Final Report of the Massachusetts Zero Net Energy Buildings Task Force” defined a zero-net energy building as “… one that is optimally efficient and, over the course of a year, generates energy on-site, using clean renewable resources, in a quantity equal to or greater than the total amount of energy consumed on-site.”

The 2006 National Renewable Energy Laboratory conference paper “Zero Energy Building: A Critical Look at the Definition” has a similar definition but highlighted the issue of the project boundary and the specific goals of the client. A subsequent technical report in 2010, “Net Zero Energy Buildings: A Classification System Based on Renewable Energy Supply Options,” further expanded the definition to consider renewable strategies ranging from on the building through to offsite renewable energy credits purchases.

In 2014, the U.S. Dept. of Energy (DOE), in partnership with the National Institute of Building Science, convened industry stakeholders to develop a universally accepted standard on the definition of ZNE. The group encouraged DOE to create a definition to allow some flexibility that is consistent and meaningful. Based on this, DOE published a request for comments in the Federal Register in January 2015, and will release final definitions in summer 2016.

Whatever the definition, however, most industry stakeholders can agree that fundamentally, a NZEB has two characteristics: enhanced energy efficiency and power generated by renewable-energy sources. The International Living Future Institute, for example, has a thorough definition of NZEB and an overview of how a building or project can be registered. New Buildings Institute provides several resources and maintains a database of verified ZNE buildings.

ZNE across the U.S.

Across the country, many states have their sights set for zero. ZNE is on everyone’s mind. From California (where the state Public Utilities Commission adopted the California Long-Term Energy Efficiency Strategic Plan in 2008) to Massachusetts (where, in 2008, then-Governor Deval Patrick convened a ZNEB task force to identify a path to move the public, commercial, and residential building sectors toward ZNE use by 2030), states are moving toward more ZNE.

California’s plan uses a number of strategies to help make all commercial buildings ZNE by 2030. Massachusetts took action on several of the task force’s recommendations including developing ZNE pilot building projects, a building asset labeling initiative, and adopting a “stretch” building energy code for local governments to consider and making the code a mandatory requirement of receiving funding and assistance through the Commonwealth’s Green Communities program.

While the efforts in both California and Massachusetts have received the lion’s share of attention, other states are making progress in ZNE. In 2009, Delaware passed a bill that requires all new commercial buildings constructed after Dec. 31, 2030, to be ZNE-capable. One step toward achieving this goal was the state’s adoption of the 2012 International Energy Conservation Code.

States are not the only ones leading the charge—many cities are also implementing ordinances and establishing pathways to achieve ZNE. For example, Cambridge, Mass., established a “Getting to Net Zero Task Force" in 2013 that is charged with putting the city on the trajectory of becoming a ZNE community. Likewise, Montpelier, Vt., is working with its stakeholders to lead the way as the first state capital in the nation where all energy needs—electric, thermal, and transportation—are produced or offset by renewable energy sources.

Policies and programs to advance ZNE

Setting sights and building a framework for increased ZNE capability is a great first step, but how do these cities and states get there? After establishing an executive order, piece of legislation, or task force, more is necessary. It is crucial to have comprehensive programs and policies in place.

In 2012, Northeast Energy Efficiency Partnerships published a white paper titled “Roadmap to Zero Net Energy Public Buildings: Recommended Steps for the Northeast and Mid-Atlantic.” Developed with input from regional stakeholders comprising state agencies, architects, engineers, utility program administrators, and energy and facilities managers, it outlines the necessary steps to get to ZNE, including a greater focus on financing, the role of the utilities, and the importance of growing the workforce. The most important message from the report is that we need to focus on five steps right now to get to zero. They include:

1. Develop a “path to highest performance” information campaign

Most often, ZNE projects are finished and we move on to the next one without ever celebrating the successes (or, in some cases, the misses) of a particular project. Developing an information campaign will ensure that stakeholders know what was involved in a particular project, what the opportunities are for future success, and how they can play a role in ensuring the building reaches its intended goal. While this process is just underway in Massachusetts, several other organizations and building owners have begun this practice, including NREL in Golden, Colo., and Bullitt Center in Seattle. The buildings have become learning laboratories not just for the occupants but also for visitors who tour the spaces taking back valuable information for their own projects.

2. Promote the continued development of exemplary public buildings

This initiative will help states transition to the next generation of high-performance buildings. Massachusetts has made this a priority by implementing the pathway to ZNE program. Two state pilot projects have been built (Dept. of Fisheries and Wildlife and the North Shore Community College Allied Health Building), and 25 more are under way that represent a cross-section of building types.

3. Prioritize measurement and reporting of public building energy performance

Incorporate a way to ensure consistent measurement of a building’s energy performance. It is great to set an energy-usage target for a building, and it is just as important to actually ensure that the building achieves it. More commonly across the U.S., transparency ordinances are being implemented to help building owners understand current energy usage. This has been demonstrated in locations like Seattle, New York, and Boston.

4. Implement stretch building energy codes

As has been the case in a majority of instances so far, Massachusetts and California are clear leaders in this regard, and have set the bar when it comes to stretch energy codes. Additionally, Vermont is rapidly emerging as a leader with last year’s adoption of Act 89, which establishes the creation of a stretch code.

While stretch energy codes can certainly set a more rigorous path forward, they are not enough. States and jurisdictions must ensure that they comply with the energy code. Robust training and education programs, with support from utility providers, are an important part of this process.

5. Create a revolving loan fund or similar mechanism to provide capital for energy investments

Often one of the largest hurdles to address for any construction project is that of financing, as lack of funding can be caused by the split between capital and operating budgets. For a ZNE project, this can prove an even greater challenge with the introduction of new technologies or practices. One solution would be to establish a revolving loan funds for efficiency invest­ments, which would then help align efforts. This is a popular practice among colleges and universities such as Harvard University. Building owners,  states, and local governments increasingly are implementing revolving loan funds to achieve their energy-efficiency goals.

Mark Walsh-Cooke is a principal at Arup, and he specializes in the design of high-performance new and existing buildings. Carolyn Sarno Goldthwaite is senior program manager of high-performance buildings at Northeast Energy Efficiency Partnerships. Her expertise is in energy codes, high-performance buildings standards, and operations and maintenance.

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