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Zero Net Energy Round Up

Alan Scott
Buildings account for a significant portion of global energy use and carbon emissions, and zero net energy (ZNE) buildings are considered an important part of the solution to climate change. This has led to a steady growth in ZNE buildings, with the acceleration of adoption driven by advances in efficient technology and the dramatic drop in the cost of photovoltaic (PV) systems. With the recent affirmation of commitment to the Paris Agreement by state and local governments, colleges and universities, and business leaders and investors in the U.S., this is likely to grow even more. So, what is a ZNE building?

Put simply, a zero net energy building is one that, on an annual basis, produces as much on-site renewable energy as it uses. However, all energy is not equal, so this simple definition led to debate about “site” versus “source” energy use and how to account for the various sources. Accounting for site energy (what the utility meter reads) treats all energy the same and ignores the impacts from extraction and processing of fossil fuels, as well as the inefficiencies of generation and transmission (e.g., 8-15 percent of electricity is lost between plant and meter). In 2015, the U.S. Department of Energy (DOE) released the now broadly accepted definition of a zero energy building that reads: “an energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy.”

Energy delivered to the site must be converted to account for the factors noted above using conversion factors for the various energy sources, based on national averages, to ensure that buildings are not unfairly credited or penalized based on the efficiency of their respective energy suppliers. While equitable for individual building comparisons, this approach ignores regional advances in grid decarbonization and local efforts with district energy and community solar. With this established definition in mind, how do ZNE buildings fit within the array of building codes, standards and certifications available today?

The DOE’s Zero Energy Ready Home certification focuses on reduced energy use, and improved health and comfort, plus design for future solar installation. A similar approach positions new commercial buildings to become ZNE in the future by designing highly efficient buildings with roof structures and electrical infrastructure to accommodate solar. Some incentive programs, including

Energy Trust of Oregon’s Solar Ready Design program, encourage this. The 2015 Seattle Energy Code takes that a step further for new construction projects, requiring a small PV system (70 watts per 1,000 SF) to be installed at the time of construction and design of a solar-ready roof for additional future capacity.

Several voluntary certification systems encourage adoption of ZNE buildings. The Living Building Challenge (LBC) Energy Petal requires projects to produce 105 percent of annual energy needs with on-site renewables (on-site fuel combustion prohibited). LBC also offers Net Zero Energy Building Certification, which requires production of 100 percent of annual energy needs, without the additional storage requirements for resilience.

Passive House certification (PHIUS) requires that projects maintain comfortable indoor environmental conditions with minimal energy inputs. It sets performance targets for heating and cooling energy demand, air tightness and source energy demand.

While creating ZNE projects today is admirable, policies and standards that push us toward future achievement are also important. One of the most well known is the 2030 Challenge, a progressive fossil fuel reduction target (currently at 70 percent) for new buildings and major renovations, using design strategies, on-site and off-site renewable energy (max 20 percent), leading to an ultimate goal of 100 percent carbon neutral buildings by 2030. To foster solutions beyond individual buildings, 2030 Districts were created to encourage public/private partnerships to drive collectively toward the 2030 Challenge goals.

Inspired by Charles Eley’s call for an alternative to the prevalent “better-then-code” energy performance metric, the Zero Energy Performance Index (zEPI) was established. It is a scalar representation of the ratio of a building’s energy performance compared to the mean energy performance of the building stock from a year 2000 benchmark. Buildings that match the benchmark earn a score of 100, and ZNE buildings score zero. Scores in between represent a percent away from zero, rather than percent better than code. The 2015 International Green Construction Code (IgCC) offers a performance compliance path for projects with a zEPI score of 50 of less.

To make it easier for building teams to measure progress, Architecture 2030 created the Zero Tool, an online application aligned with the zPEI scale that calculates the fossil fuel consumption of both new building designs and existing buildings to establish energy baselines and targets, with outputs normalized for comparison to other buildings.

California often leads the country in energy policy. That is certainly the case with their Zero Net Energy Action Plan. The residential new construction code requires ZNE for all new single-family and low-rise multifamily housing in 2020. New commercial construction must meet this standard by 2030.

The World Green Building Council (GBC) has called for all new buildings to operate net zero carbon from 2030, and 100 percent of the world’s buildings to operate at net zero carbon by 2050. Recognizing the challenge of doing this at an individual building scale, the World GBC expands the definition of net zero carbon to include on-site and off-site renewable energy production at a neighborhood, district and city scale.

When audacious goals for ZNE buildings are proposed, some like to argue about feasibility based on the narrow definitions used for individual buildings, citing the challenges of meeting on-site renewable requirements for tall buildings, energy intensive uses and projects with limited solar access. These critiques miss the point of the broader aspirations transcend individual certifications. The question is not whether ZNE is possible, only by what means is it achievable and by when.


Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with nearly 30 years of experience in sustainable building design. He is a director with YR&G Sustainability in Portland, Ore. To learn more, visit www.yrgxyz.com and follow Scott on Twitter @alanscott_faia.