MAPLE GROVE, MINN. — 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.”
Additional information is available at: www.greatriverenergy.com.