What's Happening from Environmental Building News
December 1, 2009
Two Studies Analyze Green Building Performance
Two post-occupancy energy studies are shedding some light on energy efficiency in certified green buildings. Both studies found that prioritizing energy efficiency in the design process led to better performance and highlighted the inaccuracy of energy modeling.
The first, the
Regional Green Building Case Study Project, conducted by the Center for Neighborhood Technology (CNT) and published by the U.S. Green Building Council’s (USGBC) Chicago Chapter, examined 25 LEED-certified commercial buildings in Illinois, measuring not only energy performance but also water use, greenhouse gas emissions, commute transportation, operating costs, and occupant comfort. The research stressed regular tracking of energy, water, and other quantifiable resources as a way of assessing operations and maintenance practices and improving performance. “The first step in making a building more efficient is to understand how it uses energy today. That baseline gives owners and operators the information to set and meet goals and to identify areas for improvement,” said Anne Evens, director of CNT Energy.
The study found that prioritizing energy efficiency above other LEED criteria results in better energy performance. CNT also concluded that changes in performance over time offer the best framework for a project wishing to assess its performance. No two buildings are the same, so comparisons between buildings are not always useful. Instead of relying solely on inter-building comparisons and model predictions (common practice in the industry and the method required by LEED), a building’s patterns of use, occupancy, systems improvements, operations, and maintenance over time should also be investigated, as these data provide the awareness necessary to make significant performance improvements.
A second study conducted in 2007 by the Energy Engineering Program at the University of Massachusetts–Lowell assessed six LEED-certified buildings, as well as 13 schools that were certified under the LEED-based Massachusetts Collaborative for High Performance Schools (CHPS) criteria. Researchers compared energy use predicted by modeling with measured post-occupancy energy consumption.
Researchers found that although all 19 buildings outperformed Massachusetts building energy codes, they were consuming an average of 40% more energy than predicted. A number of factors could explain the disparity between energy use predictions and post-occupancy reality, according to the study. Those discovered by the study included energy models’ failure to predict building owner and occupant behavior regarding plug loads, occupancy levels, and operating hours; and budget constraints that lead to changes in design and materials during the construction phase. Improper commissioning was to blame in some of the buildings, in which contractors incorrectly set the systems and occupants unintentionally misused the systems.
Both studies highlight the misconception that energy modeling done to document compliance with a code or standard can predict future energy use and emphasize the need for better assessment of energy performance over time. They call attention to the importance of advances like the USGBC’s new Building Performance Initiative (see
EBN Oct. 2009), which seeks to collect energy and water-use data on the approximately 4,000 LEED-certified buildings and, eventually, to benefit from the LEED 2009 requirement that projects share their data with USGBC. Better communication surrounding predictive uncertainties and improvements to green lease provisions is also needed. Essential to any solution is that owners and project teams examine their performance data on an ongoing basis and use that information to improve post-occupancy performance.
—Emily Bragonier
For more information:
Center for Neighborhood Technology
www.cnt.org
University of Massachusetts–Lowell
www.uml.edu
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