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ENERGY STAR Building Benchmarking Scores: Good Idea, Bad Science

The EPA introduced its ENERGY STAR building rating system 15 years ago. In the intervening years it has not defended its methodology in the peer-reviewed literature nor has it granted access to ENERGY STAR data that would allow outsiders to scrutinize its results or claims. Until recently ENERGY STAR benchmarking remained a confidential and voluntary exercise practiced by relatively few. In the last few years the US Green Building Council has adopted the building ENERGY STAR score for judging energy efficiency in connection with its popular green-building certification programs. Moreover, ten US cities have mandated ENERGY STAR benchmarking for commercial buildings and, in many cases, publicly disclose resulting ENERGY STAR scores. As a result of this new found attention the validity of ENERGY STAR scores and the methodology behind them has elevated relevance. This paper summarizes the author’s 18-month investigation into the science that underpins ENERGY STAR scores for 10 of the 11 conventional building types. Results are based on information from EPA documents, communications with EPA staff and DOE building scientists, and the author’s extensive regression analysis. For all models investigated ENERGY STAR scores are found to be uncertain by 35 points. The oldest models are shown to be built on unreliable data and newer models (revised or introduced since 2007) are shown to contain serious flaws that lead to erroneous results. For one building type the author demonstrates that random numbers produce a building model with statistical significance exceeding those achieved by five of the EPA building models.