It may be the most well-known standard in the building design and construction industry: ANSI/ASHRAE/IES Standard 90.1, Energy Standard for Buildings, Except Low-Rise Residential Buildings (or more commonly, ASHRAE Standard 90.1). It serves as the basis for many energy codes across the U.S. It is also the energy standard referenced by LEED and other green building certification systems.

Every few years, Standard 90.1 is updated by ASHRAE in cooperation with other organizations. With each new edition, perhaps you have wondered just how much of a difference the incremental changes in the standard would actually make in application?

It turns out that federal government wonders as well. Since 2002, the U.S. Department of Energy (DOE) has contracted comparative analyses of the latest edition of ASHRAE Standard 90.1 versus the most recent previous edition of the standard regarding energy efficiency improvements.

After completing a comparative analysis, the DOE will publish a "determination" memorandum in the Federal Register. The document provides public notice of the DOE's findings.

Determinations are publicly available on the DOE's website appear to go back as far as 2002, when the department published a comparative analysis of the 1999 edition to the 1989 edition.

Each subsequent DOE determination compares the current edition of Standard 90.1 to the most recent previous edition in terms of energy efficiency improvements related to both source energy and site energy. Though, it appears that the DOE has begun to assess relative energy cost savings, starting with the 2016 edition. The DOE also estimates energy use intensity (EUI) in their comparative analyses.

You may not be initially impressed by the incremental improvements from one edition of Standard 90.1 to the next. For instance, the DOE has determined that buildings built to Standard 90.1–2013, as compared with buildings built to Standard 90.1–2010, would result in national source energy savings of approximately 8.5 percent and site energy savings of approximately 7.6 percent of commercial building energy consumption. However, I was curious to see how the incremental energy efficiency improvements compounded over time. I ran the numbers and the results are impressive.

ASHRAE Standard 90.1-2016 improves both source and site energy use efficiency by over 40 percent compared to the 1989 edition of the standard. Figure by Daniel Overbey.



Based on data from the preliminary energy savings analysis released by the DOE, the 2016 edition of Standard 90.1 results in 46.6 percent less source energy use and 43.6 percent less site energy use compared to the 1989 edition. A staggering reduction in 27 years.

This is just one of many ways in which improved building codes and standards over time can have a profound impact on public welfare and the economy.