The New Buildings Institute (NBI) has recently asserted that 2019 is the year of the energy code, stating that “there will be a convergence of activities around energy codes that will make or break our ability to reduce the amount of carbon emitted by buildings in the next most crucial decade.” We’ll take a deeper dive into what’s behind this statement next month, but first we need to understand the concept of “zEPI,” an abbreviation for Zero Energy Performance Index.
zEPI is a concept that has been championed by the NBI (and created by Charles Eley) as a way of providing a clearer view of the pathway to net zero energy buildings and to achieving the Architecture 2030 goals. It is unique in that it references performance to a static baseline – the 2003 Commercial Buildings Energy Consumption Survey (CBECS), which provides an assessment of the energy use intensity (EUI) of buildings in the year 2000.
zEPI is a scale from 0 to 100, where 100 represents the energy performance of an average building in the year 2000 (from the CBECS 2003 survey), and where 0 represents a building with net zero energy use. The scale can extend above 100 and below 0. For example, if a building uses 50 percent more energy than an average building (of the same type) in the year 2000, then it has a zEPI score of 150. If a building uses half as much energy as the 2003 CBECS average, its zEPI score is 50. If a building is net positive, meaning that it produces more energy than it uses, the zEPI scale can also be extended below 0.
It is a much better method than the current practice of assessing performance using a “percentage improvement relative to an energy code” metric. Firstly, since code baselines and adoptions are continually changing, and with multiple versions of the model codes in use at any one time across the U.S., this comparison can be confusing and misleading. Instead of goal setting as a percentage better than an existing code, zEPI sets a constant goal of zero, from which one can then assess how far away a particular building performance or code version is from that target. It is thus forward looking, rather than backward looking.
Moreover, it also provides a unified scale for all building types both existing and in-design, since all buildings are compared to their CBECS 2003 average by occupancy type. For example, a commercial building’s performance is compared to that of the CBECS 2003 average commercial building to get a zEPI score. Likewise, a warehouse’s performance is compared to the CBECS 2003 average performance for warehouses to get its zEPI score. zEPI has already been adopted as a metric in the International Green Construction Code (IgCC) starting with the 2015 version and is used to define the requirements for performance path compliance.
The chart illustrates the zEPI scale, showing the performance of current model and local energy codes and the Architecture 2030 challenge performance targets on this scale, and the pathway to net zero by the year 2030. Encouragingly, based on this information, it looks like the Architecture 2030 target for carbon neutrality in new buildings is achievable if the current linear trajectory of model and stretch codes is maintained. Of course, there is a significant gap between model code publication and state adoptions and therein lies one of the major challenges of making the needed progress. Of equal importance is the need to continue increasing the stringency of our model codes to stay on the trajectory to net zero in 2030. More on those issues next month.
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