CHAMPAIGN, Ill., 8/24/22: Last year, a multidisciplinary team of scientists and engineers helped build a geothermal exchange system to heat and cool a new building at the University of Illinois Urbana-Champaign (U of I), saving electrical usage and marking another step in the quest for a carbon-neutral campus. This type of heating and cooling system is also used successfully in homes, businesses, and industry, according to Illinois State Geological Survey (ISGS) scientist Andrew Stumpf.

Stumpf, ISGS colleagues Yu-Feng Lin and Steve Sargent, and staff at U of I’s Facilities & Services (F&S) partnered with U of I engineering professors Tim Stark, Tugce Baser, and Roman Makhnenko and their students from the Department of Civil and Environmental Engineering (CEE) to help develop a geothermal exchange system for the 124,000-square-foot Campus Instructional Facility (CIF).

The engineering firm dbHMS, hired by F&S to design the geothermal exchange system, estimates that it can supply about 65 percent of the building’s energy load and will last for at least 50 years. Overall, dbHMS projects that the building’s greenhouse gas emissions will be reduced by more than 70 percent compared to emissions from similar-sized buildings with conventional heating and cooling systems, resulting in savings of $45,000 per year or $1.35 million over the system’s lifespan.

Geothermal energy has been considered a viable alternative to the use of fossil fuels and is an uninterruptible and reliable source of heating and cooling with a low impact on the electrical grid. The geothermal exchange system installed at CIF circulates water through geothermal loops in 40 boreholes that are connected to heat pumps in the basement. Conceptually, geothermal loops transfer heat from the building into the ground in the summer and capture any residual heat in the ground for heating in the winter.

“In Illinois, the ground below about 40 feet stays at a constant 55 degrees F, which makes heating and cooling more efficient because the temperature is not fluctuating throughout the heating and cooling seasons,” Stumpf said.

Furthermore, geothermal exchange systems are much more efficient, from 400 to 500 percent, than a traditional natural gas furnace that typically is 90 percent efficient. Geothermal exchange systems also require only one piece of equipment—a geothermal heat pump—that replaces both a furnace and air conditioner.

Another benefit is that the geothermal heat pump is in the basement, which provides a level of security and resiliency to the energy grid in case of harmful effects from storms and natural disasters or when the sun does not shine or wind blows, Stumpf said.

As part of the CIF system design, the project team investigated the subsurface geology through a geothermal monitoring well. Core samples collected in the first 355 feet of the borehole drilled were tested for their physical, hydrological, thermal, and mechanical properties in labs at ISGS and CEE. This work was done to characterize the complexity of the subsurface geology that impacts the movement of heat underground.

Ground temperatures in the 385-feet-deep borehole are being measured using fiber optic cables. The initial measurements provided baseline ground temperatures that were used to fine-tune the design of the geothermal exchange system. In the long term, the measurements will help F&S know how the ground reacts to running the geothermal exchange system and whether it is heating up. The geology under campus, which includes the Glasford glacial sand and gravel aquifer, plays an important role in the process of transferring heat into and pulling it out of the ground. Groundwater both stores heat and moves it away, depending on the hydrological conditions.

With the baseline temperature data and thermal conductivity of core samples, dbHMS was able to revise the initial borefield design and reduced the number of wells from 60 to 40, which saved significant drilling costs that are projected to reduce the project payback period, or time it takes for the system to pay for itself, from 40 to 28 years. Typically, the largest expense of installing geothermal exchange systems is drilling the boreholes, which accounts for over 50 percent of the project cost, Stumpf said.

“Although the upfront costs of geothermal exchange systems are higher than buying an air conditioner and natural gas furnace without a government incentive, the long-term economic implications work out to be much better, as the annual heating and cooling savings from running a geothermal heat pump system are such that the system pays for itself in 15 years or less, and after that you’re saving money,” he said.

Over a 30- to 50-year lifespan, the system is more cost-effective than conventional heating and cooling systems.

More information about the project was recently published in ISGS Circular 606, which is available on the U of I IDEALS digital repository for research and scholarship.

This is one of several projects on campus that have or are considering geothermal exchange systems. The recently passed federal Inflation Reduction Act provides new financing programs to build more of these systems.

Stumpf has also been instrumental in creating the Illinois Geothermal Coalition, a new research collaboration at the U of I, whose mission is to strengthen and advance the implementation and design of geothermal energy systems in the Illinois and the Midwest. The coalition comprises researchers, industry professionals, corporate and non-profit entities, and educators seeking to establish Illinois as a leader in geothermal energy.

----

Media contact: Andrew Stumpf, 217-244-6462, astumpf@illinois.edu
news@prairie.illinois.edu