Great River Energy Headquarters
Setting a Green Example: A non-profit electric co-op brings open-space office design and unique energy-saving strategies together under one roof.
Maple Grove, Minnesota, looks like any other new suburban development—until you see the wind turbine. At 166 feet, it looms over big-box stores and strip malls. One of a few urban wind towers in the United States, the turbine is the most visible landmark of Great River Energy’s (GRE) new LEED-Platinum headquarters and is emblematic of the forward-thinking electric cooperative’s vision for the future.
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Having outgrown its previous headquarters, GRE sought a new home that would model energy-efficient building strategies, foster a collaborative office culture among its more than 400 employees, demonstrate a commitment to energy conservation, and—not least of all—push limits. “We wanted to do something that hadn’t been done before,” says Tom Lambrecht, GRE’s sustainable growth and development leader. The $57-million, four-story building designed by Perkins+Will’s Minneapolis office, opened on Earth Day in 2008 and has been turning heads ever since; GRE member outreach coordinator Jennifer Shaput has led building tours for more than 8,000 visitors.
Responding to the desire for an open, collaborative, daylit space, Perkins+Will created a flexible design on a 7-foot-by-10-foot module with shallow floorplates divided by two four-story atria.
The team refined the layout with Ecotect modeling software and daylight modeling at a University of Minnesota lab. Low partitions and high ceilings allow daylight penetration. Daylight sensors activate artificial lighting only when necessary, and sunshades in the atrium can be controlled from the reception desk in response to employee requests.
The layout also democratizes the space and makes heating and cooling efficient. Most work areas were brought toward the center and circulation areas were left at the perimeter, meaning that no individual workspace monopolizes the view. Closed perimeter offices have glass openings to the inside, allowing daylight into interior spaces. “This way everyone owns the perimeter,” explains Russell Philstrom, AIA, an architect with Perkins+Will. Philstrom also credits early charrettes for the success of the space-efficient design, noting that the final design was 25 percent smaller than initial sketches. “Front-loading design and efficiency early in the process ended up saving GRE a lot of space” and construction costs.
The team chose innovative and energy-efficient mechanical systems: underfloor displacement ventilation combined with water-to-water heat pumps for heating and cooling. Releasing ventilation air slowly through manually controlled diffusers in a pressurized underfloor plenum allows occupants to control their environment. It also eliminates the high-horsepower fans needed in a conventional ducted system.
The team explored several heat pump options, first drilling bore holes to gauge the potential for a ground-source heat pump, and eventually settling on an efficient “lake coil” system: 34 miles of 3⁄4-inch-high-density polyethylene tubing submerged in a 6-acre, 32-foot-deep lake (a remnant from earlier gravel excavation on the site). This system circulates water through the mechanical system at temperatures between 39 and 60 degrees Fahrenheit, providing free cooling to the building core from October to June and significantly reducing compressor energy consumption.
After conserving energy, the team tried to produce as much renewable energy on site as possible. Between the 200-kW wind turbine (a refurbished Vestus model) and the 72-kW photovoltaic (PV) array, GRE draws about 15 percent of its power from onsite renewables when the systems are at capacity, or about 7–8 percent on the average day. Informational kiosks in the central atrium provide feedback on wind and PV performance in real time.
After considering a green roof system, the team went with a more cost-effective white polyolefin roof, mitigating the heat-island effect and lowering cooling loads. Rainwater from the rooftop is collected in a 20,000-gallon cistern, treated with ultraviolet light, and used for toilet and urinal flushing; overflow is piped to a rain garden. Indoors, washrooms are equipped with low-flow fixtures; outdoors, native and adapted plantings further reduce potable water use. Together these water-efficiency strategies save 80–90 percent of the potable water typically consumed in a similar building.Attention to local materials led the team to select wheatboard cabinetry and limestone from nearby Mankato, Minnesota. Green tile made from recycled glass bottles appears in kitchens and common areas throughout the building, and 87 percent of wood is FSC-certified. Additionally, the post-tensioned concrete frame is cast from a mix that replaces nearly 50 percent of the cement with fly ash from its own operations, significantly reducing embodied energy; GRE now sells 98 percent of the fly ash it produces for use in similar applications.
As a project that strives to change attitudes toward buildings and energy use, much of the GRE headquarters’ success may be in front of it. The community has not completely warmed up to the wind turbine in their midst, and the renewable systems have been slow to reach their expected output. “With a unique system you have unique issues,” says Philstrom. After working with the team fine-tuning the systems through a year of measurement and verification to get them functioning as designed, Philstrom offers an important lesson: “It takes a patient design team to have a high-performance building.”
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