LEEDing Gardens to the Sun

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Rice Plant Conservation & Science Center
Daniel F. & Ada L. Rice Plant Conservation and Science Center.
Living Green Roof
The building’s green roof and PV modules.
Rice Plant Conservation & Science Center
Living Green Roof

When the Chicago Botanic Garden decided to build a state-of-the-art plant science center, one of their goals was to achieve Leadership in Energy and Environmental Design (LEED) Gold certification. In 2010, one year after the building opened, they did just that. The Daniel F. and Ada L. Rice Plant Conservation and Science Center, which houses laboratories devoted to the study of plants and soil, received points in six categories, including sustainable sites, water efficiency, and energy.

To qualify for LEED Gold, the design team, from Booth Hansen Chicago, hired consultants from the nonprofit energy-efficiency think tank Rocky Mountain Institute (RMI). The construction documents were already complete by the time RMI joined the team, and they made numerous suggestions that resulted in rethinking the entire project. “The biggest energy consumption is the mechanical systems,” says Jean O’Brien Gibbons of Grumman/Butkus Associates, the project’s engineering consultants. “We really had to stop and re-evaluate all the systems.”

“They initially figured, ‘Oh, we’ve missed all our opportunities,’” says Cara Carmichael, a senior consultant for RMI. “But that wasn’t at all the case.”

One of the key design upgrades RMI made was to add more energy-efficient clerestory windows—reducing lighting energy consumption in the atrium by 79%. These low-e windows, along with the building’s sloped roof, bring light into the building’s inner offices. Light sensors were added to automatically extinguish artificial lighting when natural light reaches a threshold level.

Other suggestions by RMI included the use of recycled materials, such as flooring that incorporates rubber from shredded tires, metal shavings mixed with epoxy for bathroom countertops, and a wall from a black walnut tree that previously stood on the site. Twenty percent of the building’s construction consists of recycled materials (half post-consumer and half pre-consumer). Fifty percent of wood used on the project was Forest Stewardship Council-certified.

Water efficiency is maximized through a rainwater catchment system that surrounds the building—including the parking lots. The runoff flows into a bioswale where native plants naturally cool and clean it. This water flows into a lake and is used on site to irrigate plants. Another water-saving strategy included the planting of native plants for landscaping, which reduces the need for irrigation by 50%. In addition, the building uses 30% less water by using low-flow plumbing fixtures and valves.

One of the building’s most notable features is its green roof. While the advantages of green roofs are becoming well-known, such as reducing heat gain in the warmer months, this one has an important difference. The 16,000-foot garden serves as an outdoor laboratory, as many new varieties of plants are tested to see which are best suited for rooftop planting in the Midwest.

The roof also features a 54.7 kW batteryless grid-tied PV system, which offsets about 5% of the building’s electricity use, saving the Garden more than $10,000 per year. The Sanyo bifacial modules produce power from both sides of the module, and may produce up to 130% of its STC rating, depending on the albedo (reflectance) at a site. The modules installed at the Plant and Science Center get approximately 5% to 10% of their energy from reflected light.

The HIT Double Bifacial modules were chosen because they had the highest efficiency rating at the time. They were also considered aesthetically appealing, since you can see through them from below. The decision to use a zero-degree tilt was also an aesthetic one—though this necessitates cleaning at least twice a year, as recommended by their installer, Habi-Tek. Another factor that went into the choice of this PV system was the ability of installers to complete their work entirely from above. The subarrays are cantilevered over the edges of the building, helping provide shade to windows and plantings around the building’s perimeter.

—Kathy Kelley

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