Cascadia POE Shows Encouraging Results

Jessica Boehland and Rachel Auerbach

A new post-occupancy evaluation (POE) from the Cascadia Region Green Building Council (CGBC) shows generally positive energy performance and user satisfaction with the region’s LEED® certified buildings. The January 2006 report, “LEED Building Performance in the Cascadia Region: A Post-Occupancy Evaluation Report,” examined 11 of the region’s 31 LEED certified buildings that had been occupied for at least one year as of September 2005. The group includes five offices, two libraries, and four multi-family residential buildings.

Much of the POE focused on the buildings’ energy performance. Analyzing information obtained from building owners, CGBC found that six of the ten buildings with design-phase energy modeling used an average of 30% less energy than those models predicted. One outlier, the study’s only anonymous building, used three times more energy than it was projected to use, and the remaining three used an average of 27% more energy than their projections. Nine buildings also had base-case models showing how much energy a similar, but conventionally designed, building would use; all nine came in below these baselines, by an average of 39%.

Cathy Turner, an environmental performance measurement consultant who prepared the report for CGBC, says “on average, over all the buildings in our study, actual performance was about the same as the design.” She notes, however, that a range of factors can skew the performance of any individual building away from its predicted energy use. These include changes to the design or construction and usage patterns that differ from the assumptions in the models. The intent of the energy models is to determine differences among versions of a building’s design with most factors held constant. As Turner says, “the objective is not usually to accurately predict the total energy use of a building.”

While the buildings’ energy efficiency has been encouraging, their water efficiency has, for the most part, been disappointing. Of the seven buildings with design projections, six used more water than expected, by an average of 33%. Turner believes this indicates a flaw not in fixture performance but in usage assumptions. “There are few good studies of things like how frequently office occupants use a faucet, or how long they leave it on when they do use it,” she says.

The study also included a survey to determine occupant satisfaction with a range of building qualities.Users reported being somewhat dissatisfied with acoustics but satisfied or very satisfied with all other indicators. The results show that occupants are very satisfied with the buildings overall but slightly less satisfied with their personal workspaces. After “building overall” and “workspace overall,” the most positive scores went to light level, air quality, and visual comfort. “Green building aims to reduce energy use while also creating buildings that occupants prefer to work in. But some may be concerned that energy savings could make the space less comfortable,” says Turner. “So the consistently good perceptions of temperature, lighting, and indoor air quality in this study were encouraging indicators that these buildings are doing it right.”

“Green building has some lofty goals,” said Turner. “We have a good theoretical basis for expecting our green building techniques to deliver these results,” she says, but measuring actual performance can ensure they are operating as intended while also guiding the design of other buildings and identifying areas for further research. CGBC hopes the POE will encourage others to undertake similar studies. “I’m looking forward to seeing more results emerge,” says Turner.

This article was produced by BuildingGreen, Inc.- www.buildinggreen.com

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