Duluth Energy Systems

Duluth Energy Systems

Modernizing a Legacy Energy System

Duluth Energy Systems is the city-owned energy system that provides heating and cooling service to the city’s downtown and Canal Park. Ever-Green Energy has served the system since 2012 and works closely with the City of Duluth to provide exceptional service and advance the system to better serve the community.

Shortly after taking over operations and management responsibilities, Ever-Green completed a system master plan to:

  • Improve efficiency
  • Increase reliability
  • Enhance environmental stewardship
  • Improve cost-competitiveness
  • Identify opportunities for growth

During planning, Ever-Green identified the distribution system as a major opportunity to improve operations and made plans to transition 16 blocks of the steam distribution system to hot water, concurrent with a major public works project.

Ever-Green is now leading system advancement, including design of the new hot water distribution system, customer building conversions, plant conversion, and construction management.

The steam to hot water conversion for this major segment was completed in 2020. By 2024 more than 50% of the system will have transitioned from steam to hot water services.

Another major initiative has been the natural gas pilot that has significantly reduced the amount of coal used for heating. Since 2012, coal usage has been reduced by nearly 98%. The coal reduction and efficiency efforts have reduced greenhouse gas emissions by 20% in that timeframe. Additional renewable integration is under consideration for the next phase of system advancement.

Ever-Green’s Role

Ever-Green serves as the system operator and manager. Ever-Green works closely with the City of Duluth to determine the strategic direction of the system, practical investments to keep the business competitive, and align with local policy and environmental initiatives. Our team has guided the system through enhancements to the system’s operational and maintenance processes, including inventory management, operating and maintenance crew structure, work planning, performance monitoring, and trending of key parameters. Ever-Green reviewed the debt financing of the system and recommended changes, which enabled the system to enter into long-term contracts with customers and use revenue bonds for future debt financings.

Recent areas of technical focus have included customer development, efficiency improvements, carbon reduction (through reduction of coal and plant and distribution improvements), a steam to hot water transition, and future renewable integration.

About the City of Duluth

The City of Duluth is a port on Lake Superior in Minnesota with a population of about 86,000 people. The City has made its energy future a priority and has seized opportunities to work within the community, with its utilities, and in collaboration with experts from around the country to integrate state-of-the-art technology and international best practices for an efficient, cost-effective, and environmentally advanced system.


Ever-Green supported the City in its effort to gain community support and state funding for system upgrades. This project has engaged experts and supporters from within and beyond Duluth, including state commissioners, city councilors, and executives from the business, energy, environmental communities who believe in Duluth’s grand energy vision.


Buildings served with district Steam164 Buildings
FY 2015 energy sales111,870 MWh
Total Building Area Served5.6 million square feet

Steam Sources

Two coal boilers25 MW ea
Two Coal / Gas boilers28 MW ea
Pipe Diameter1-inch to 20-inch
Pipe Length59,000 feet
Supply Pressure150 psi
Reliability rate99.992%


Buildings served with district hot water6 Buildings
FY 2015 energy sales17,360 MWh
Current billed demand2.65 megawatts
Total Building Area Served0.5 million square feet


Exhaust steam from auxiliary turbines
(augmented by main steam as required)
Pipe Diameter4-inch to 12-inch
Pipe Length6,900 feet each, supply and return
Volume100,000 gallons
Supply Temperature190-220 degrees F
Return Temperature160-190 degrees F
Supply Pressure40 psi
Reliability rate99.992%


Buildings served with district cooling5
FY 2015 Energy Sales366,382 ton-hours
Building Area Served0.53 million sq. ft.


Chiller Plant 401 W First Ave
One Steam Absorption Chiller800 tons
Pipe Diameter4-inch to 12-inch
Pipe Length4,800 feet each, supply and return
Volume of distribution system15,600 gallons
Supply Temperature42 degrees F
Return Temperature56 degrees F
Supply Pressure30 psi
Minimum pressure differential15 psi
Reliability rate99.990%