Re-evaluation of the NBI LEED Energy Consumption Study
A recent study by the New Buildings Institute looked at the energy performance of 121 LEED certified commercial buildings and concluded they were saving 25-30% energy relative to conventional buildings. Here we identify several critical flaws in the NBI analysis and, upon reexamination of the data, reach different conclusions. We find that the average energy consumption by LEED certified buildings is actually higher than the corresponding average for the US commercial building stock. This difference is shown to be largely due to the over-representation of “high-energy” principle building activities (PBA’s) such as laboratories and the under-representation of “low-energy” PBA’s such as non-refrigerated warehouses in the LEED building data set, relative to their occurrence in the U.S. commercial building stock. Eliminating high- and low-energy PBA’s from both data sets yields “medium-energy” building subsets free of these disparities. Comparing these we find that LEED medium energy buildings, on average, use 10% less site energy but no less source (or primary energy) than do comparable conventional buildings. LEED office buildings achieve 17% reduction in site energy, but again, no significant reduction in primary energy use relative to non-LEED office buildings. We further find that these results do not change significantly if LEED buildings are compared with newer vintage, non-LEED buildings. As green house gas (GHG) emission correlates with primary energy, not site energy, we conclude that LEED certification is not yielding any significant reduction in GHG emission by commercial buildings.
Scofield, John. 2009. "Re-evaluation of the NBI LEED Energy Consumption Study." In Proceedings of the International Energy Program Evaluation Conference (IEPEC), Portland, OR, Aug. 12-15, 2009: 765-777.
Physics and Astronomy