Groundbreaking low-carbon geothermal project might emerge in Prospect Park

The drilling came to an abrupt halt on the eastern edge of Minneapolis last Monday when the crew blew a hose. The engineers were drilling down through the layer of sandstone to reach the underground Shakopee and Jordan aquifers, in the hopes of pioneering a new energy system that could be a leap forward for decarbonizing Twin Cities homes.

Though the drilling rig stood a good 25’ high, it was still dwarfed by the massive abandoned grain silos that have long stood sentry over this overlooked part of town. Dubbed the Towerside district, the triangle of land along the BNSF rail yard between the Surly Brewery, the University of Minnesota and Minneapolis’ Prospect Park neighborhood might soon be one of the most energy efficient communities in the state.

“It looks like drilling a hole,” admitted Nina Axelson, who works for Ever-Green Energy, an environmental consulting and planning firm that specializes in district energy systems. “That’s one advantage of aquifer thermal energy storage; you do fewer wells and so you don’t need as much land.”

Unlike a traditional geothermal heating system, the proposed aquifer energy would use existing underground water as a kind of thermal storage system. With help from a grant from the McKnight Foundation, the test wells will measure the flow rate of the two aquifers to see if they would work.

Such an aquifer system would be groundbreaking for the United States. Technically called Aquifer Thermal Energy Storage (ATES), these systems are more common in Europe, particularly in The Netherlands.

The way it works:

A loop of pumps it set up between buildings, two aquifers, and a heat exchanger. Using the two aquifers as thermal batteries, warm water would be pumped from buildings through the exchanger in the summer, replaced with cool water from the ground. In wintertime, the process would run in reverse, heating buildings with the warmer water.

When running properly, the system would reduce energy costs by 40%, and would pay for itself within the first few years. If built, an ATES system, with some tweaks to regulation, could work particularly well for places like Minneapolis that see large seasonal swings in temperature.

“Aquifer-thermal, even the name’s pretty new,” said Cam Gordon, who was on hand for the drilling. Gordon is the Green Party City Council member who has represented this area for a decade and has long been pushing for more aggressive climate change policies in the city. He views a district energy system as a great way to make low-carbon buildings the default for the neighborhood rising along the Green Line.

“It’s getting slowly developed,” Gordon said of the so-called Towerside neighborhood. “This project is apartment buildings, and hopefully in the future we’ll have some manufacturing or job producing businesses.”

According to Gordon, the developer, John Wall, supports alternatives to fossil fuel heating in his planned projects. Working with the City of Minneapolis and Ever-Green, they are trying to get ahead of potential development by thinking early about alternatives.

A district system would be a big change because most new apartment construction in Minneapolis offers heating and cooling through inefficient individual units attached to each apartment, what Gordon calls “magic-paks.” Because they are all separate units, these units lack the efficiencies that come from having a centralized HVAC system.

The proposed district system offers the opposite approach. Not only would heating and cooling be set up for buildings, a whole neighborhood could connect to a single facility through underground water pipes. Because it allows for alternatives at scale, district systems are the gold standard for energy efficiency.

“This is a key point looking at alternatives for energy,” said Gordon. “This system could be expanded and could serve more buildings.”

Gordon hopes that the proof of concept might help the city consider district energy systems at other large developments, like the Upper Harbor Terminal buildings planned for the north Minneapolis riverfront.

Even now, the long-neglected land south of the rail yard is already beginning to see transformation. Hundreds of new apartments have already been constructed along the Green Line, and a new food hall is opening up this year in a derelict warehouse.

The new neighborhood is part of a long-term plan that dates back to Green Line light-rail planning. During those years, a group of Prospect Park neighbors began working on ambitious plans for the area north of University Avenue, which they hoped would become a mixed-use hub. Dubbed the Towerside Innovation District, there’s even a nonprofit pushing a vision of the area as a business and environmental incubator that might connect entrepreneurs with the University of Minnesota.

The potential energy system is just one of the “district systems” envisioned by the planners.

According to Gordon this kind of groundwork has been a huge help for thinking about large-scale projects like the proposed ATES system.

“Having a neighborhood that says we would really welcome more density helped push it,” said Gordon. “The city’s now on record united saying we want to lead on climate change.”

Just hours after the drilling halted, with a new hose in hand, the crew recommenced their boring job.

“To inject heat from buildings in the winter, the Aquifer’s heating well and cooling wells need the water not to move very fast, so heat stays there,” explained Ever-Green Energy’s Nina Axelson, describing how the test drilling will install a “flow sensor.”

Once the test wells are in place, they’ll collect data about how fast the water underneath the sandstone is flowing. Finding out those rates are critical to the success of the project, as low rates of movement will allow the water to work as a thermal battery, while high rates of movement would make the storage system impossible.

If all goes well, construction could begin on the new housing with occupancy sometime in 2022, complete with geothermal heat. It might finally cure an Achilles heel for decarbonizing Minnesota cities, where perhaps the solution, in the form of underground water, has been under our feet this whole time.