A new energy scale is getting some attention lately and I wanted you to know a little bit about it.

It’s called the zEPI scale for energy and it stands for Zero Energy Performance Index (zEPI). It is part of a larger movement of “outcome-based” energy codes and building disclosure ordinances (Seattle, NYC and Washington DC now all have ordinances that require buildings to benchmark their energy use and disclose it to the public – think of it as MPG stickers for buildings).

In the last month zEPI has come up a number of times:

• PAE is using it for client energy standards that we are currently writing.
• Earth Advantage is using it in their new commercial building rating system which was piloted in Portland and will be launched nationally this year.
• Our friends at the New Buildings Institute are a big fan of it.
• It is being adopted into the 2012 International Green Code.

The basis for zEPI can be traced back to a scale presented in a paper written by Charles Eley called Rethinking Percent Savings. Eley makes the compelling case for the adoption of a more stable, absolute scale that would be used to benchmark buildings as opposed to the percent-better-than-code baselines (ASHRAE 90.1 2004, 2007, etc.) which are continuously shifting as more stringent codes are developed and adopted. The scale establishes zero net-energy as the absolute goal. This makes the need for a baseline obsolete; the only measurement that matters is how far a building deviates from zero net-energy. The scale would go from 0-100, with 100 representing the average energy consumption based on 2003 CBECS (Commercial Buildings Energy Consumption Survey) data.

The absolute nature of the zEPI scale has made it easily applicable to code language, and it is currently written in draft form into the ICC’s new Green Code (IgCC). NBI has become a big proponent of zEPI because it sets a constant goal (zero) and shifts the conversation from percent better than code to percent from zero, which is the kind of market shift we believe needs to happen if net-zero is to ever be fully realized.

Credit: Paul Schwer, PE, LEED AP
Paul has more than 30 years of experience in mechanical system design and is a national leader in engineering for high performing and sustainable buildings. He has been president of PAE since 2004.