St. Paul is preparing to replace a decades-old steam boiler system at Como Zoo and Conservatory with geothermal energy as the capital city moves toward a goal of carbon neutrality in municipal buildings within the next decade.

The geothermal system, which will use groundwater to heat and cool buildings, is expected to reduce the zoo's carbon emissions by at least half. The city is partnering with Xcel Energy and a local geothermal energy company to study which aquifers to use, where to begin retrofitting and how much it will all cost.

"The city is spending … hundreds of thousands, if not millions, every year on heating and cooling Como and maintaining that old system," said Jimmy Randolph, founder and chief technical officer at geothermal company Darcy Solutions. "It makes a lot of sense to put in a more efficient system for them."

The City Council on Nov. 18 voted unanimously to allocate $8,114 from the city's Energy Conservation Loan Fund to help pay for the study. Xcel will cover the remaining $24,342.

St. Paul's Climate Action and Resilience Plan aims to make city buildings carbon neutral by 2030 and to reach carbon neutrality citywide by 2050.

Most carbon emissions in the city come from buildings, followed by travel, St. Paul officials say.

St. Paul has already explored replacing Como's steam energy system with hot water, which estimates showed would cost $2 million to $3 million, according to city Energy Coordinator Jim Giebel. That solution would also use natural gas, which the city is trying to reduce, he said.

Zoos and aquariums around the world are taking similar steps. The Association of Zoos and Aquariums, which represents more than 230 facilities in the United States and overseas, reported last year that 56 facilities were either buying renewable energy or generating it on site.

Geothermal energy has been around for decades and is generally considered the most energy-efficient way to heat and cool buildings, Randolph said.

The version that Darcy Solutions would install at Como would save money and space by transferring heat underground between water from the building and groundwater, without consuming or contaminating the groundwater — technology that Randolph started developing several years ago as a research scientist at the University of Minnesota.

Giebel said upfront costs would likely be comparable to a hot water system, though with far greater cost savings down the line — the geothermal system would likely pay for itself within a decade, Randolph said.

Once the feasibility study is complete — likely early next year — it will be a matter of finding the money to pay for the upgrade, Giebel said.

"We're in the first inning, I guess," he said. "We've got a ways to go."

Emma Nelson • 612-673-4509