Jonathan Hall, GGLO

From Al Gore to Vanity Fair, many are finally recognizing the link between global warming and sustainable design. Rating systems, including the U.S. Green Building Council’s (USGBC) LEED, the U.S. Environmental Protection Agency’s Energy Star, and multiple other local programs, define sustainable building using their own criteria. But how can we confirm the buildings we call “sustainable” are truly performing as they were designed?

Post occupancy evaluations, performed at least one year after occupancy of a building, provide actual and measurable results of a building’s energy and water use. Only after such an evaluation can we tell whether the building is working as we intended. GGLO undertook a multi-year study reviewing and comparing conventional and green developments, which provided quantifiable results while also clarifying the intangible benefits of sustainable design.

Climate change and green building
The global warming crisis has forced us to look at buildings in new ways and attempt to understand the impacts they have on the environment. Considering building operations consume almost half of the energy used in the United States, the need for high performance buildings becomes obvious. Both the American Institute of Architects and USGBC recently adopted the 2030 Challenge, promoting 50 percent energy reduction in all new buildings increasing by 10 percent every 5 years until achieving carbon neutrality by 2030.

As more organizations join the 2030 Challenge, the need to be able to measure the actual energy savings of a green building will become even more important. Energy modeling, the traditional method of predicting a building’s performance, is based on predictive assumptions about building operations and user habits.

Although such models may prove quite accurate, they are only educated guesses. To determine actual energy and water savings in buildings we design, our firm gathered information from utilities to evaluate whether the assumptions we made during the design process were playing out in the real world.

Balancing the numbers
Comparing the information from utilities to the energy modeling data, we discovered energy modeling can be a relatively accurate predictor of energy use. For the buildings we modeled, the actual utility usage was within 10 percent of predicted usage. Water usage, on the other hand, fluctuated greatly from modeling, averaging 35 percent off our estimated values. The results suggest the variable of differing user habits is pronounced in water use, and tells us we need to better predict occupants’ use and provide better education to tenants about the environmental and economic impacts of water use.