Multiple ZNE Definitions: So Mysterious!

By Sofia Siegel

If you missed the Net Zero 2017: Energy + Water + Waste Conference on August 24th, 2017, you missed a day of thoughtful, solutions-based thinking and progressive case studies. Speakers presented on zero waste manufacturing, zero net energy facilities, and ZNE community development. The audience learned about successes, challenges, and lessons learned; if you did miss it, you can review the presentation slides here.

At the start of the day, Verdical Group posed several survey questions to get a better understanding of the attendees’ knowledge set, and understanding of ZNE projects and processes. The final survey question (more specifically, the results) struck me:

Leaders in our field are clearly divided on this crucial point, in an important moment. California is just two years away from what we expect to be a MAJOR code shift: The California Public Utilities Commission (CPUC) and California Energy Commission (CEC) launched the Residential New Construction Zero Net Energy (ZNE) Action Plan as pathway to actualizing the California Long-term Energy Efficiency Strategic Plan’s goal of 100% of new homes achieving ZNE in 2020. This is projected to be adopted into code when Title 24 is next updated; the 2019 Standards will go into effect on January 1, 2020.

As an industry, we are preparing for a shift to ZNE requirements for new Residential projects in 2020, and Commercial buildings in 2030.

From the California Residential ZNE Action Plan, “A zero net energy (ZNE) building produces as much energy as it consumes over the course of a year. These buildings achieve ZNE first through high levels of energy efficiency, and then through the addition of clean, on-site renewable power generation, typically solar PV.” The language driving the code update is leans toward Site ZNE, but but more of our attendees selected Zero Emissions as the best definition of ZNE. However, no one definition achieved majority consensus from attendees; even among leaders and decision-makers in this field, the waters are murky.

Rather than try to convince you of the best definition, please see comprehensive definitions below, and we would love to hear from you! All five of the Net Zero 2017 Conference survey questions and the results can be found here.

Time Dependent Valuation (TDV):

TDV is based on the concept that energy efficiency measure savings should be valued differently, depending on which hours of the year those savings occur, to better reflect the actual costs of energy to consumers, utilities, and society. The TDV method encourages the design of buildings that perform better during periods of highest energy costs.

Zero Emissions:

A Zero Emissions Building generates or purchases enough emissions-free renewable energy to offset emissions from all energy used in the building over the course of a year. This metric compares CO2 GHG emissions related to energy use in the building.

Source ZNE:

A Source ZNE building generates as much energy as it consumes over the course of a year, based on the amount of energy consumed by each energy source (weighted). This includes all site energy, plus energy consumed in extraction, processing, and transport of primary fuels, and energy losses (thermal combustion and in transmission / distribution to building site). This definition converts all energy sources into a common unit (kBtu) using different factors for each source, in order to assess and ensure all energy is offset.

Site ZNE:

A Site ZNE building generates as much energy as it consumes over the course of a year, based on the amount of energy used within the building site boundary. This excludes the energy losses that occur off-site, (generation, transmission, distribution, etc), so this metric is not necessarily consistent with building energy bills. The simplicity of calculation helps make this tool useful for ZNE calculations. This definition converts all energy sources into a common unit (kBtu) using different factors for each source, in order to assess and ensure all energy is offset. The on-site renewable generation requirement is typically larger than that for Source ZNE or TDV.

What definition do you like best? Why? Tweet at us @VerdicalGroup with your thoughts!