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Summary
The Minnesota city has made significant investments in its aging district energy system, adding natural gas boilers and replacing steam pipes with hot water loops.
The city of Duluth, Minnesota, continues to lower emissions from downtown buildings as it expands a redesigned district heating system.
Originally built in 1932, the system acts like a shared boiler for a network of buildings in the city’s core. Over the last decade, the city has mostly phased out coal, converting two of its four boilers to run on natural gas. More recently it began replacing old steam pipes with a more efficient closed-loop system that circulates hot water between customers’ buildings and its centralized plant.
The investments are a critical component of the city’s effort to cut carbon emissions by 80% by 2050, as the heating plant that powers the district energy system is by far the largest source from city government operations. The system serves more than 160 customers and covers 5.6 million square feet of building space.
“The biggest benefit of the new system is that it will generate less energy but heat the same amount of square feet,” said Terry Nanti, general manager of Duluth Energy Systems, an affiliate of St. Paul-based Ever-Green Energy that operates the system for the city of Duluth. “When we reduce the amount of energy we produce, we reduce our reliance on coal.”
In January, warmer than typical weather allowed the system to rely exclusively on the newer gas units, burning no coal at all for the first time in its 90-year history. Overall, annual coal use is down about 80% since 2012. Even gas emissions have declined by 20% as the system has grown more efficient.
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