Researchers drilling under a college campus in the 1980s paved the way for an ambitious new project in the Twin Cities.
By Phil McKenna
ST. PAUL, Minn.—Nearly half a century ago, the U.S. Department of Energy launched a clean energy experiment beneath the University of Minnesota with a simple goal: storing hot water for months at a time in an aquifer several hundred feet below ground.
The idea of the so-called seasonal thermal energy storage was to tuck away excess heat produced in summer, then use it in the winter to warm buildings.
Now, 45 years after the first test wells were drilled under the university’s St. Paul campus, one of the first large-scale aquifer thermal energy systems in the nation is being built less than 10 miles from the original test site.
The Heights, a mixed-use development rising from a former golf course on the city’s Greater East Side, will tap thermal energy from an aquifer 350 to 500 feet below ground. Groundwater drawn from wells spread across the northern half of the 112-acre development, coupled with high-efficiency electric heat pumps powered in part by solar panels, will provide low-cost heating and cooling with little to no greenhouse gas emissions for 850 homes and several light-industrial buildings.
The U.S. Green Building Council recently designated the project, led by the Saint Paul Port Authority, a LEED Platinum community. That’s the industry group’s highest level of sustainability certification.
The aquifer will provide steady 50-degree temperatures as a starting point for heating in the winter and cooling in the summer. Depending on the specific needs of future tenants, the groundwater could also serve as a thermal battery, storing excess heat in the summer for use in the winter, said Michael Ahern, senior vice president for system development at Ever-Green Energy, the firm designing the heating and cooling system.
The system will be one of the first large-scale aquifer thermal energy projects operating in the United States since the Department of Energy field tests in the 1980s.
Since then, more than 3,000 similar systems have been built worldwide, with the vast majority in the Netherlands, according to a study published last year in the journal Clean Technologies and Environmental Policy. Only two such systems exist in the United States, the study found. Inside Climate News confirmed the existence of a cooling-only system constructed in 2005at what is now the campus of Stockton University in New Jersey. A second aquifer thermal energy storage system, which provides heating and cooling for one building at Fort Benning, a U.S. Army post in Georgia, was completed in 2015.
Marc Hoyer, a retired scientist who worked for the Minnesota Geological Survey and the University of Minnesota, served as a project manager on the aquifer thermal energy storage tests in St. Paul in the 1980s. The system they were evaluating included temperatures in excess of 212 degrees Fahrenheit, far higher than what is now being proposed for The Heights.
At the time, he and other Survey members took turns sleeping in a trailer next to wells, waking each hour to record temperature and pressure gauge readings as part of their round-the-clock monitoring of the system’s performance.
