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Researchers working on geothermal exchanges at Epic Systems
September 13, 2022

Going underground to heat and cool top-level facilities

Written By: Alex Holloway

University of Wisconsin-Madison researchers are helping the U.S. government improve energy efficiency at an array of federal buildings.

James Tinjum, an associate professor of civil and environmental engineering and director of the geological engineering program at UW-Madison, is leading a university research team on a multi-institutional effort to expand deployment of geothermal heating and cooling exchanges at government facilities.

Geothermal exchange systems—also called geothermal heat pumps or GeoExchange—use the earth like a battery, relying on the relatively constant temperature of the ground, which is warmer than the air above in winter, and cooler in the summer.

“We circulate liquid through a series of pipes that are typically about 500 feet (150 meters) underground,” Tinjum says. “By doing that, we’re transferring heat into the earth during the summer to provide cool air, and we are withdrawing heat in the winter to warm our buildings and heat our domestic hot water.”

Geothermal exchange systems can generate tremendous efficiency improvements because mechanical heating and cooling systems don’t have to work as hard to provide conditioned air. For example, on a 90-degree day, a typical air conditioning unit has to work hard to lower the temperature of the ambient air it draws in. With a geothermal exchange system, the unit circulates liquid that’s already been cooled through circulation within the earth that is at a relatively constant 55 degrees, drastically reducing the amount of energy needed to produce a comfortable indoor temperature.

Because space conditioning accounts for so much energy usage in the United States (Tinjum says it consumes about 40 to 60 percent of energy in businesses and homes), lowering the amount of energy we dedicate to heating and cooling could have big ramifications for sustainability efforts across the country. That’s especially true for the federal government, which consumes nearly 1% of all end-use energy in the United States, making it the largest single energy consumer in the country.

And these efficiencies are ones that the UW-Madison team has seen firsthand. Epic Systems in Verona, Wisconsin, has a geothermal exchange field with thousands of wells in it. Tinjum and his research group have worked with Epic for a decade to monitor its geothermal network using a fiber-optic system they developed to collect distributed temperature measurements across district-scale geothermal exchange fields.

At the time the researchers deployed the fiber-optic monitoring network to the geothermal exchange field at Epic, the field had 2,500 bores in it. The system delivers fresh data every 10 minutes, collected from along roughly 8.5 miles of fiber-optic cables distributed across the geothermal exchange field. With the data, the group aimed to help Epic operate the field as efficiently as possible, while monitoring the field’s temperature through the seasons.

Their work saw some big results.

“At Epic, the system operates at an incredible coefficient of performance of 10, which means that only one unit of input energy is needed for 10 units of heating/cooling,” Tinjum says. “That project really put us at the forefront of the industry, with some of the papers we’ve prepared and presentations we’ve given—some of which led directly to our current project with the Department of Energy.”

On that project, which runs for two years, Tinjum is collaborating with CEE Associate Professor Dante Fratta and Wisconsin Geological and Natural History Survey hydrogeologist David Hart. They’ll have two graduate students and several undergraduate researchers to assist.

The group is part of a coalition with Oak Ridge National Laboratory, the National Renewable Energy Laboratory, Lawrence Berkeley National Laboratory, Pacific Northwest National Laboratory, Illinois State Geological Survey, International Ground Source Heat Pump Association, and Oklahoma State University to install test wells at up to five U.S. Department of Defense locations. The Department of Energy’s Office of Energy Efficiency and Renewable Energy is backing the project with up to $6 million in grant funding.

Photo caption: Associate Professor James Tinjum’s (right) research team has worked on geothermal exchanges at Epic Systems in Verona for years. Now they’re putting that expertise into a project to support the federal government’s efforts to bolster energy efficiency.