True measure of success

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.

The post-occupancy study confirmed sustainable buildings come at an almost negligible cost increase over conventional buildings, and result in measurable utility savings. Of the three buildings in our study designed to LEED standards, the cost increases ranged from 0.5 percent to 1 percent of the total hard and soft construction costs. Financial incentives available from a variety of sources cut cost increases in half and the yearly savings on utility bills averaged another 1 percent. After one year of occupancy, the green design features actually begin earning the project money.

Connecting the dots
We began the building evaluation process in 2005 and found most of the published information from previous post-occupancy studies addressed commercial or office buildings. The lack of information available on green multi-family buildings, which are a core component of the work GGLO does, led the firm to perform our own post-occupancy studies. We felt the need to demonstrate to our clients the accuracy of our predictions by providing quantifiable, measurable and repeatable results. We studied seven multi-family projects (five designed by GGLO). The buildings are a mix of affordable, market-rate, sustainable and traditional design. Our studies have shown the measures undertaken in each of our multi-family buildings to save energy and water have worked. The average energy savings for sustainable buildings was 30 percent when compared with their conventional counterparts and the average water savings was 20 percent. The results have also shown the energy modeling performed for each of the buildings during the LEED certification process was accurate enough to predict building energy usage. (See Fig. 1) Water usage does not follow the modeling as closely, suggesting our assumptions may need to be reviewed.

None of buildings studied had aggressive energy goals or implementation efforts. Building owners took advantage of incentives offered by local utilities by installing increased insulation, thermally efficient windows, fluorescent lighting in common areas, efficient central boilers, and accurate and programmable thermostats. The projects did not have operating systems that were overly complex or innovative; rather, simple systems, combined with the improved building envelope, saved the project owners a significant amount on their utility bills. Each strategy produced a measurable benefit in water savings.

Next steps
Our results show simple steps taken for increasing water and energy savings can be effective and accurate. By monitoring more of our projects, we can use the results to implement energy and water saving measures earlier in the design process. Results from our studies show the buildings designed to meet LEED Certified and Silver levels are not reaching the levels of the 2030 challenge. Our designs need to be more innovative to meet this critical benchmark.

Jonathan Hall is a senior associate and sustainable building advisor specializing in urban, mixed use, affordable and sustainable projects at GGLO architecture and planning firm. Alicia Uhlig and Dan Bertolet of GGLO contributed to this article.