Subsurface Characterization, Monitoring, and Modeling of a Geothermal Exchange Borefield for the Campus Instructional Facility at the University of Illinois at Urbana-Champaign

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This report presents the outcome of research in geothermal energy, specifically geothermal exchange, conducted by geologists, hydrogeologists, and engineers at the Illinois State Geological Survey and Illinois Water Resources Center in partnership with engineering faculty and students in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana- Champaign (U of I), who are members of the newly-formed Illinois Geothermal Coalition. This effort brought together a multi-disciplinary and multiorganizational team of scientists and engineers who are focused on advancing the application of geothermal energy technologies for district heating and cooling systems that allow energy end users to meet net carbon neutrality, renewable energy, and grid resilience goals.

The research specifically supported the design and operation of a shallow geothermal exchange system for the U of I and its private partners at the Campus Instructional Facility (CIF) that just recently came online in April 2021. As academic campuses aggressively pursue renewable and sustainable energy sources to reduce their carbon footprints and enhance operational resiliency, geothermal energy has increasingly garnered more interest and is considered an uninterruptible source of heating and cooling, offering greater dependability in supplying a constant energy load with the least impact on the energy grid. Geothermal energy is very attractive because of its long-term environmental and economic benefits, especially since heating, cooling, and dehumidification systems in buildings are the largest emitters of greenhouse gases (GHG) and are estimated to consume more than 40% of the nation’s electricity.

At the U of I, the administration and students are pursuing an aggressive strategy to obtain a sustainable campus environment and become carbon neutral by eliminating or offsetting GHG emissions as soon as possible, and no later than 2050. At the CIF, the goal is to exceed the per-building metrics proposed in the 2020 Illinois Climate Action Plan (iCAP) by connecting the geothermal exchange system with radiant heating and cooling as part of an energy-efficient design that is expected to save ~2,839 million Btu (MMBtu) of energy per year and reduce GHG emissions by >70% compared to similarsized buildings. Nearly 65% of that energy load (~135 tons of heating and cooling capacity) will be supplied by the geothermal exchange system.

Unlike in western regions of the U.S. where hot fluids and steam in volcanic rocks are used to generate electricity or for direct heating, in the Midwest region geothermal energy systems typically use thermal exchange technologies that take advantage of the thermal energy stored in the Earth’s subsurface (typically within the upper 100–150 m [~330–500 ft]). Using geothermal heat pumps, refrigerant fluid or water is circulated through boreholes allowing heat to be absorbed or released to the ground (e.g., Lund 2002). The geothermal exchange system takes advantage of the constant ground temperature throughout the year below depths of ~10 m (~33 feet). The ground temperature below this depth is not impacted by seasonal changes in atmospheric conditions, and thus ground-based heating and cooling systems run more efficiently. Furthermore, geographic areas such as the U.S. Midwest region have a consistently variable climate (e.g., cold winters and hot summers), which can maximize the benefits offered by utilizing the natural thermal energy from the ground.

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