I have been spending this week at the American Council for an Energy Efficient Economy’s (ACEEE) Summer Study on Energy Efficiency in Buildings. Yesterday I presented a paper that summarizes my findings from an 18-mos study of the science behind the EPA’s ENERGY STAR building rating systems.
The title of my paper, “ENERGY STAR building benchmarking scores: good idea, bad science,” speaks for itself. I have replicated the EPA’s models for 10 of their 11 conventional building types: Residence Hall/Dormitory, Medical Office, Office, Retail Store, Supermarket/Grocery, Hotel, K-12 School, House of Worship, Warehouse, and Senior Care. I have not yet analyzed the Hospital model — but I have no reason to believe the results will be different. (Data for this model were not available at the time I was investigating other models. I have since obtained these data through a Freedom of Information Act request but have not yet performed the analysis.)
There are many problems with these models that cause the ENERGY STAR scores they produce to be both imprecise (i.e. have large random uncertainty in either direction) and inaccurate (i.e., wrong due to a errors in the analysis). The bottom line is that, for each of these models, the ENERGY STAR scores they produce are uncertain by about 35 points! That means there is no statistically significant difference between a score of 50 (the presumed mean for the US commercial building stock) and 75 (an ENERGY STAR certifiable building). It also means that any claims made for energy savings based on these scores are simply unwarranted. The results are summarized by the abstract of my paper, reproduced below.
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.
In subsequent posts I will elaborate on these various findings.
This type of scientific critique is crucial to accountable building performance assessments. If we do not know the accuracies of the voluntary or mandatory benchmarks, the likelihood of improved performance is diminished. Thank you for yor dilligence!
Fantastic paper John. I will be circulating it widely and hope that other readers will do the same. It is a very important and crucial paper for discussing policy in the escalating arena of green rating systems, benchmarking, and code changes. Unfortunately much of this area is not subject to scientific reasoning of any kind, let alone a studied response to solving difficult problems.
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