Denver Launches Thermal Energy Loop to Decarbonize Downtown Buildings

Denver will replace its downtown steam system with an “ambient loop” that circulates tepid water through underground pipes linking large buildings. Water-source heat pumps at each site draw heat from the loop to warm interiors or reject heat to cool them. The Cherokee Boiler House, filled with “rattling pipes, hazard signs and cockroach carcasses,” will serve as the loop’s control hub.

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The steam network, built in the late 1800s, now powers over a hundred downtown structures but is leaky, costly, and dependent on natural-gas combustion. A 2021 ordinance requires large buildings to cut greenhouse-gas emissions, a target many deem unattainable while the steam system remains.

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The pilot will initially serve 11 city-owned buildings, expanding to nine by 2030. Construction costs are estimated at $280-$320 million, a range the city says is up to 75 % cheaper than other decarbonization options. Geothermal boreholes over 1,000 feet deep will tap Earth’s heat, while wastewater heat in winter can equal four times the energy used by current steam-heated buildings. Denver targets net-zero emissions by 2040.

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Mayor Mike Johnston described the loop as a “future of energy” that can provide affordable heating and cooling. The Office of Climate Action explained that water-source heat pumps move heat wherever it is needed, allowing buildings to share thermal energy. Drew Halpern called the Cherokee Boiler House the system’s “brains and brawn,” coordinating temperature regulation. City officials acknowledge the $280-$320 million upfront cost and plan to fund the pilot with municipal dollars, a state grant, and future bonds or private investment.

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Dan Freedman noted that sewage-derived heat is less compelling than geothermal and expressed optimism that the system could succeed if the pilot works.

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• “We think we are standing in what can be the future of energy in Denver, which is both pollution free and affordable.” — Mike Johnston, Mayor of Denver

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• “If you can come to one of the most bustling, vibrant downtowns in the world and discover any one of those buildings is heated and cooled by water, that is a breakthrough for the city and, I think, a breakthrough for the country.” — Mike Johnston, Mayor of Denver

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• “Basically, heat pumps can move heat wherever you need it.” — Elizabeth Babcock, Head of Denver's Office of Climate Action, Sustainability and Resiliency

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• “If we're being honest, geothermal just sounds sexier than wastewater thermal.” — Dan Freedman, Director of Technology and Innovation, Metro Water Recovery

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A micro-loop will be installed in about two years to serve two buildings and a sidewalk snow-melt system. By 2030 the city aims to connect nine buildings, with plans to expand the model to thousands of downtown natural-gas customers if the pilot proves successful.

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