Sustainable: Aquifer project offers green energy model

By District Energy posted 04-06-2021 12:25


Finance & Commerce


Prospect Park may soon be the home of one of the largest projects ever built in the United States to heat and cool large buildings using underground aquifers.

Test wells underway now should confirm the viability of employing an aquifer system for heating and cooling two apartments and one proposed office building in Towerside Innovation District, a 370-acre area north of University Avenue between the University of Minnesota and Highway 280. The project is a collaborative effort that includes district energy consultant Ever-Green Energy, Towerside, the developer Wall Cos., and Minneapolis.

Using a technology called aquifer thermal energy storage, or ATES, the Towerside project would tap underground water to help heat and cool buildings. Advocates for the approach like ATES because it uses no natural gas for heating and employs a district energy system that creates greater efficiency. Commercial and residential buildings are the most significant greenhouse gas source in Minneapolis, partly because of natural gas heating.

Just as geothermal systems extract the Earth’s warmth for heating and cooling, ATES systems do the same with underground water. Both methods fall into a category called “geo-exchange” that draws heat from water or the ground for cooling and heating buildings. For example, Carleton College uses geothermal heat for its campus, and San Francisco will use bay water for a district energy system around the Giants’ stadium neighborhood.

An ATES comes with distinct advantages for dense neighborhoods like Towerside. The system creates separate cold storage and warm storage wells for district heating and cooling, using heat exchangers before circulating water through buildings. In summer, cold water gets pumped through facilities to cool them. When the water returns, it goes into the warm storage aquifer. In colder weather, the warm water supplies heat pumps, heats buildings and discharges the now cold water into the cold wells for storage in the aquifer.

Mark Worthington, president of Underground Energy, worked on the Towerside project and explained the process. “You have this concept of a seasonal flow reversal,” he said. “You extract from the cold well in the summer and warm well in winter.” He said no water is consumed in an ATES and the wells take up much less space than would an equivalent closed-loop geothermal system.

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