25 Case Studies: Evaluating Green Buildings After Construction

By Doug Widener

Building green is only the beginning. Without practiced operations and properly gauged utility use, a sustainably built structure is no different from its traditionally built neighbors. But with an understanding of operational issues, tenant behavior and maintenance practices, building owners and managers can implement ongoing changes that lead to improved building performance and sustainability over time.

An important component towards understanding how our buildings work and how they can work better is a recently released report exhibiting case studies of local green buildings.

The Regional Green Building Case Study Project: a Post-Occupancy Study of LEED Projects in Illinois summarizes the first year of a multi-year study to analyze the post-occupancy benefits of twenty-five LEED-certified projects in Illinois. The study was funded by the Grand Victoria Foundation and is a collaborative endeavor between the USGBC-Chicago, U.S. EPA Region 5, the City of Chicago, Delta Institute and the Center for Neighborhood Technology, which was the lead researcher for the project.

While this project is neither the first nor the largest study to analyze the costs, benefits or post-occupancy energy performance of LEED projects, it is unique both in its scope and collaborative approach. This project is one of the first post-occupancy studies to employ such a broad scope of metrics, including energy use, greenhouse gas emissions, water use, commute transportation, construction & operating costs, green premium, health & productivity impacts, and occupant comfort. It is also among the first to collect multiple years of post-occupancy data and provide ongoing analysis of initial participants while adding additional projects in subsequent years.

As expected, the study found that sustainability does not stop with planning and construction. While a building may be designed to be green, it is often ongoing operational activities that affect the amount of energy, water and other resources it consumes.

“Sustainability must be integrated into ongoing operations and maintenance practices,” says Kathy Tholin, CEO of the Center for Neighborhood Technology. “Constructing to LEED Platinum was a natural choice given CNT’s long-standing commitment to sustainable development,” explains Tholin. “But our job is far from complete. Now that we’re utilizing the space, sustainability means focusing on ongoing operations and maintenance. We’re striving for continuous improvement.”

Resource use, the study also found, varies in LEED buildings. Many participating projects performed better than conventional commercial interiors and buildings, with projects that focused on energy conservation as a part of their LEED strategy performing better in relation to energy use and conservation than projects that focused on other areas of sustainability. Given that LEED is a multifaceted system that rates a building’s sustainability on a variety of factors, projects that focused on energy conservation performed better in this area than projects that did not. All buildings in the first year of the study were certified under older versions of LEED; newer versions of the rating system mandate—and motivate—higher levels of energy efficiency.

The measured performance results of these twenty-five Illinois LEED projects are a snapshot in time of these specific buildings. Extrapolating the results from this data set to represent the performance of all LEED projects in Illinois, or all LEED projects in general, is not valid. It is expected that another set of participants will yield different results because of the mix of unique buildings and building activities. It is also quite likely that the performance of these same projects will change over time due to occupancy, operations, maintenance and systems changes.

All LEED projects in Illinois were eligible to participate in this study if they could provide at least twelve consecutive months of post-occupancy energy use data. The twenty-five study participants represent projects certified at all LEED levels and several project types from new construction to existing, from commercial interiors to core and shell. The projects range in size from 3,200 to 4.2 million square feet and represent a variety of building activities including education, hospitality, mixed use, office and others. Each property was gauged on seven categories: energy use, greenhouse gas emissions, water use, construction and operating costs, cost of building green, health and productivity impacts and occupant comfort.

For analysis of the buildings’ energy performance, the report used the EUI metric, or energy use intensity. The EUI is calculated as kBtu/square feet/year and applies to all fuel types. The projects were split into two categories for energy performance analysis: whole project energy use and partial energy use. For the seventeen properties in the whole project energy use category, complete energy data was provided for a building or project space, including heating, cooling, lighting and load attributed to the building occupants. The median EUI for whole project energy use project participants in the Illinois LEED Study was 94. Only partial energy data was provided for the eight projects in the partial energy use category. For example, a tenant in a Commercial Interiors (CI) space provided the electricity bill for lighting and plug load when their heating and cooling costs are built into the lease and/or not metered. The median EUI for partial energy use project participants in the Illinois LEED Study was 38.

The Illinois LEED projects that focused on energy optimization credits (LEED NC EA Credit 1) and achieved a higher number of EA Credit 1 points performed better. Separating projects by principal building activity, it appears that those that achieved a higher number of EA Credit 1 have a lower EUI. It is not surprising that projects that prioritize energy efficiency as a key LEED strategy are likely to perform better than those projects that do not focus on energy efficiency or those which prioritize points in other LEED categories. Yet, the Illinois LEED project sample size is small and further research is needed to determine if there is a statistically significant association.

One of the profiled projects, the Evelyn Pease Tyner Interpretive Center in suburban Glenview, was designed with the aim of achieving “zero energy” status. Solar panels, a geothermal system and a vegetated roof all contributed to this, but so does the building’s orientation and facade. By setting the building on an east/west axis, solar gain was mitigated through the use of large overhanging eaves on the south wall while minimal eaves to the north and 20 foot high windows provide visitors incredible views of the prairie. Operable windows in every space allow prevailing breezes to ameliorate temperatures without using energy. Careful attention to cross ventilation design means that the building is comfortable in the summer without mechanical systems running.

The median water use for the Illinois LEED study projects was 7.7 gallons/square foot/year and 5.9 gallons/occupant/day. No projects submitted water data separating interior from exterior water use, though two projects indicated no water was used for exterior landscaping. The wide range in annual water use is from fifteen thousand gallons to more than thirty-three million gallons, and is attributed to individual project size, principal activity and occupancy.

Despite the water-intensive business of Christy Webber Landscapes on Chicago’s west side, water resources have been effectively managed. Variable flushing toilets and low flow fixtures reduce domestic water use by 30%. Rain water shedding off the 10,000 square foot shop building is collected into a dual system of cisterns which, combined, can hold more than 32,000 gallons of water and supply a large portion of the watering needs for the landscape company.

Employees from nine profiled projects took part in an optional transportation commute survey. The transportation analysis focused on three metrics: vehicle miles traveled, transportation energy intensity (calculated from vehicle miles traveled in passenger vehicles) and use of amenities for LEED points. The study’s participants had shorter commutes (9.2 miles one way, compared to the national average of 12.1 miles) and averaged 18,608 kBtu/employee/year in transportation energy intensity.

All nine projects surveyed earned alternative transportation credits as part of their LEED certification. These credits came as the result of public transportation access, bike storage and carpool-preferred parking. The data collected suggest that employees do not often understand what employer transportation policies, amenities and services are available to employees such as pre-tax transit benefits, guaranteed ride home or compressed work schedules. Onsite food service or kitchen facilities were the most commonly utilized amenity.

The Center for Neighborhood Technology, who acted as project researcher and whose building was included in the research sample, recognizes that the energy spent commuting to and from the office is an important component of an organization’s environmental impact and, as a result, location was an important factor in the decision to stay and renovate their building in Chicago’s Wicker Park neighborhood rather than move to a new site. Consequently location also plays an important role in CNT’s overall greenhouse gas emissions. Only 28% of the staff’s commute miles are in passenger vehicles. Even though staff members occasionally drive to work, most (83%) report using alternative transportation modes as their default commute mode to work.

The study’s cost analysis suggests that, similar to conventional buildings, construction costs vary widely and may be attributed to principal building activity and an individual project’s goals and specifications. The median study construction cost was $211/square foot (fifteen projects reporting). The median green premium was 3.8%, however, eight projects stated a reduction in operating costs.

The main campus of Saint Xavier University on the south side of Chicago estimates the cost premium to reach LEED Gold for its Rubloff Hall was 2.8%. However with longer-life building features and lower operating costs, payback should be reached in less than 5 years. Rubloff Hall’s energy efficiency can also be evaluated by comparing the annual use of gas and electricity to two conventionally built residence halls on campus with similar floor plans and size, Morris Hall and McCarthy Hall. While Morris purchased $32,000 in natural gas and McCarthy $34,000 for the fiscal year 2006-2007, Rubloff required only $19,000. Similarly, the two traditionally-built residence halls consumed over $37,000 and $50,000 worth of electricity each, contrasted with Rubloff’s $30,000.

Ongoing performance measurement and analysis is critical to quantify a building’s environmental impacts and efficiency over its lifecycle. A building’s performance changes over time, so future building performance evaluations must incorporate and interpret the impact of changes in individual building use, occupancy and operations and maintenance, as well as systems improvements. Three of the case study projects discuss how their operations have changed post-occupancy and the resultant impact of the changes on their buildings’ energy use. Studies such as this Illinois LEED Study are vital in that they provide building owners valuable feedback that can inform continuous improvement strategies.

A building’s best benchmark is its own performance. Individual building measured performance allows building owners to set realistic, achievable and continuous improvement goals. Since every building is unique in its use, occupancy, operations, maintenance and systems, actual post-occupancy measured performance that reflects actual operating conditions of the specific building will be the best benchmark. Comparisons to other buildings (LEED and non-LEED) or any modeled predictions are temporal or limited in use, even as methodologies and data sets evolve to provide more accurate comparisons.

To support building performance initiatives, more research is needed on standardized metrics, data collection protocols and tools, appropriate benchmarks and routine post-occupancy evaluations. Specifically, more data and research methodologies are needed to quantify the health and productivity benefits of green buildings, market-driven financial benefits and risks and impacts of building location on building performance—particularly the energy and greenhouse gas emissions associated with transportation to and from the building.

Educating the design/build community on green practices is very important, but educating owners and managers is just as necessary. “I can’t imagine a sustainable business without a sustainable work place. Yet even after having this office in place for several years, I am struck by how resistant to change building owners are,” said Doug Farr, President of Farr Associates, whose Monadnock Building offices were part of the study. “It is tragic that given how easy it is to do, they choose to do things the wrong way; even given that a sustainable workplace enhances the quality of work life.”

As this study recommends, measured, ongoing building performance evaluation supports important and distinct research goals. These evaluations are critical at the individual building level to provide understandable, relevant and actionable feedback to building owners, operators and occupants. And further testing and evaluation can inform, and improve, the green building movement as a whole.

Doug Widener is Executive Director of USGBC-Chicago, the mission of which is to lead the regional transformation of the built environment to become ecologically sustainable, profitable and healthy through education, advocacy and collaboration. To read the full report, visit www.usgbc-chicago.org.


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