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The Great River Energy headquarters is a four-story, 166,000-square-foot building located on a 12.5 acre site in Maple Grove, Minnesota’s Arbor Lakes development, completed in April 2008. Nearly 15 percent of the building’s required electricity comes from renewable energy, including an on-site 200 kilowatt wind turbine. The 166-foot tall refurbished wind turbine is visible to drivers on nearby Interstate 94, and provides approximately ten percent of the building’s power needs. The building also features a 72-kW array of photovoltaic panels mounted on the roof and at ground level that transforms solar energy into electricity for about five percent of its energy use. A geothermal heating and cooling system utilizes the adjacent Arbor Lake, a six acre, 32-ft. deep man-made lake, which is the energy source for the building’s HVAC system. The lake water provides cool enough water to cool the core of the building without refrigeration due to the high supply air temperature requirement of the displacement air system, with less than a 1°F change in water temperature in the lake.
By Andrea Ward, Green Source Magazine
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.
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 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, the architects 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, the building’s designer. 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.”
The following article about the GRE mechanical system is from Contractor Magazine
By Candace Roulo
Electric utility leads by example: headquarters is Platinum LEED certified
Great River Energy’s headquarters, located here, is the first commercial building in the state to receive U.S. Green Building Council’s Leadership in Energy and Environmental Design Platinum certification. The 166,000-sq.ft. four-story building consumes approximately 50% less energy than Minnesota code requirements, uses less water than comparable buildings and saves approximately $90,000 in annual energy costs thanks to an in-lake geothermal HVAC system and in-floor displacement ventilation system, on-site solar panels and wind turbine, an efficient plumbing system and many more sustainable products installed throughout the building.
The building was completed in April 2008 and received LEED certification last September. The building is located on 12.5 acres next to Arbor Lake, a six acre, 32-ft. deep man-made lake, which is the energy source for the building’s HVAC system.
GRE is an electric generation and transmission cooperative that serves two-thirds of Minnesota. It provides wholesale power to 28 distribution cooperatives in the state and Wisconsin, distributing electricity to approximately 1.7 million people.
Since GRE is an electric generation and transmission cooperative, with a mission to provide members with energy at competitive rates in a sustainable environment, it is fitting that the company focused on building a sustainable facility, showcasing, on a daily basis, that utilizing renewable energy does indeed conserve resources.
According to GRE’s White Paper, the cheapest and cleanest kilowatt-hour is the one that is not produced. Hence, conservation and energy efficiency is GRE’s “first fuel.”
Arbor Lake was the most efficient source to use for the HVAC system since the building was located near it, but before the geothermal lake system was chosen, a water energy analysis program study was done. Geothermal Design Associates Inc., Fort Wayne, Ind., conducted the study. Results concluded less than a 1°F change in water temperature in the lake.
“The geothermal lake system was the most efficient system because the lake water provided cool enough water, most if not all year, to cool the core of the building without refrigeration due to the high supply air temperature requirement of the displacement air system,” said Dale Holland, PE, LEED AP and executive vice president of mechanical at Dunham, the Minneapolis-based mechanical contracting firm that worked on the GRE project.
In the lake’s heat exchange system, propylene is mixed with water and pumped through 34 miles of ¾-in. high density polyethylene piping, PE3408 IPS, manufactured by Charter Plastics and provided by HD Waterworks, and 39 heat exchange bundles, manufactured by Loop Group Inc., at the bottom of the lake. In the summer, heat from the building interior is extracted, and, in the winter, heat from the lake is absorbed.
“The most unique aspect of the building systems is that the lake produces water at the almost optimum temperature to serve the displacement ventilation, thus, significantly reducing the energy consumption of the building,” explained Holland.
In the building’s mechanical equipment rooms, heat pumps manufactured by Water Furnace and York fan coils are organized by zones, providing heating and cooling to different areas in the building. There are 70 air-to-water heat pumps of which 47 are dedicated to the perimeter zones, offsetting skin heat gains and losses. Seven fan coil units provide core building displacement ventilation air to the raised floor. More than 20 fan powered VAV terminals serve mostly individual conference rooms for cooling and ventilation.
Because a raised access floor, manufactured by Tate Access Floors Inc., was used in the building, under-floor displacement ventilation was installed by Doody Mechanical, St. Paul, Minn. This type of ventilation system delivers warm or cool air to employees through in-floor air diffusers that throw air horizontally. Individuals control air flow in their work space with an adjustable vent. Floor level air is supplied at 65°F -68°F and is driven by natural convection.
“The displacement air system provides a pool of cool air only a few inches above the floor,” said Holland. “Because this air is cooler and therefore heavier than the room air it tends to stay at the floor elevation until it detects a rising plume of air from a heat source near the floor. When the heat source is provided, the cool air near the floor rises in the plume and cools the person or other heat source like a computer.”
According to Great River Energy’s White Paper, this is one of the first times a geothermal heating and cooling system and under-floor displacement technology have been used together.
The plumbing system uses rainwater harvesting and low-flow plumbing fixtures to conserve water. Rainwater and snowmelt are collected by roof drains, filtered and stored in a 20,000-gal. underground cistern by Total Containment Solutions and provided by Zahl Petroleum. The water is filtered in a water treatment system, using a small amount of hydrogen peroxide to sanitize the water. The graywater is then used in toilets and urinals.
The low-flow strainers on sinks and showers, and American Standard low-flow urinals and dual-flush low-flow toilets are predicted to reduce water use by 66%, according to GRE’s White Paper. Sloan low-flow 0.5 GPM aerators and motions sensors are used with Sloan bathroom faucets and dual flush meters on toilets.
Also, rainwater used strictly for irrigation is collected in a pond. GRE uses captured rainwater to water the property when needed based on an agreement that was created with the city of Maple Grove. Site storm water is directed through a filtration pond and into the city’s storm water pond before being used.
The building also conserves energy by taking advantage of renewable energy sources. Approximately 14% of its required electricity comes from an on-site 200 kilowatt (at full output) wind turbine and 72 kilowatt (at full capacity) photovoltaic panels, manufactured by Sanyo, mounted on the roof. At ground level, solar energy is transformed into electricity.
According to GRE’s White Paper, the building is predicted to receive approximately 10% of its energy from wind and 3-5% of its energy from the photovoltaic panels. This is enough energy to power approximately 50 homes annually.
Great River Energy bought the refurbished turbine, originally manufactured in Denmark, from Energy Management Services. The turbine’s gears were remanufactured and the generator was rewound to change the speed to a one-speed turbine, increasing efficiency.
“Great River Energy’s headquarters is a model of ways to use energy more efficiently and a signal that traditional construction methods can be improved,” said Dan Becchetti, communications coordinator at GRE. “Since construction was completed in April 2008, thousands of people have toured the building and learned about its sustainable features. Not everyone will build to Platinum LEED level, but if people can learn one or two ways to save energy from the building, the energy savings down the road will be invaluable.”
Great River Energy’s headquarters features:
• Consumes 50 percent less energy than Minnesota code requires.
• 40 percent less electricity used for lighting than buildings using standard
• Uses 90 percent less water than comparable corporate campuses.
• Recycled more than 90 percent of construction waste.
• Produces up to 15 percent of the building’s annual energy use with on-site
renewable energy resources.
• Excess electricity is distributed on the local electric grid.
• Constructed with recycled and locally manufactured materials.
• Saves nearly $90,000 in annual energy costs, with a payback in seven years for
energy efficient technology and renewable energy (energy efficiency paybacks
alone are approximately four years).
• A low-energy HVAC system design featuring under-floor displacement
ventilation and a geothermal heating and cooling system that utilizes the adjacent
Arbor Lake. The technology results in a dramatic improvement in indoor air
quality, energy savings and workplace productivity compared to buildings that
use standard HVAC technology.
• Nearly 15 percent of the building’s required electricity comes from renewable
• An on-site 200 kilowatt wind turbine. The 166-foot tall wind turbine is
visible to drivers on nearby Interstate 94.
• A 72-kW array of photovoltaic panels mounted on the roof of the building
and at ground level transform solar energy into electricity.
• Dimming ballasts, daylight sensors and motion sensors help reduce artificial
lighting needs; the new headquarters harvests daylight through narrow office floor
plates and multiple light-filled atriums. With reduced lighting requirements, there
is less heat generated from lighting, reducing the need for air conditioning to cool
the building. Artificial lighting is high-efficiency fluorescent.
• The building uses 40 percent less energy for lighting than similarly sized
buildings that use standard technology.
• A longer east-west orientation of the building maximizes daylight harvesting.
• Windows on the ease and west walls are kept to a minimum to reduce unwanted
solar heat gain.
• The facility’s concrete structural frame contains nearly 50 percent fly ash, the
product created when coal is burned to generate electricity. Fly ash from Great
River Energy’s Coal Creek Station was used in both the structure as a
replacement for cement, and in the carpet backing. Using fly ash in construction
decreases the amount of waste sent to landfills and reduces energy used to
• Energy efficient elevators use 60 percent less energy and require less space. The
elevators use a counterbalance mechanism and high-efficiency motors.
• Sustainable landscape features such as rain gardens and native plantings and
vegetation. Rainwater is used for on-site irrigation and filtered for use in flushing
• Local construction materials were used when possible, including Mankato
limestone and Lake Superior granite.
• More than 90 percent of construction waste was recycled.
• The building was the first commercial building in Minnesota to receive LEED Platinum certification (September 2008).
Great River Energy Brochure (806 kb)