Drew Halpern, senior energy project manager with Denver's Office of Climate Action, Sustainability and Resiliency, tells ENR the city views district thermal infrastructure as a way to avoid the scale of electrical system expansion that widespread building electrification could require.

But the engineering challenge shifts elsewhere.

“The geothermal piece is probably the most complicated part,” Halpern says, noting that broader deployment could require drilling hundreds of deep wells while navigating dense underground infrastructure and constrained urban sites.

A June 2025 ambient-loop feasibility study identified potential geothermal locations beneath parking lots and other downtown sites. While the wells themselves would not prevent future construction of a larger-scale buildout, excavation, foundations and future structures would require careful coordination among city agencies, building owners and utilities, among other vested interests.

Broader deployment could ultimately involve approximately 500 geothermal wells drilled to depths approaching 1,200 ft and distributed among multiple downtown locations, Halpern says.The concept also includes converting the former Cherokee Boiler Plant into what he described as the system's future “brains and brawn”—a central hub designed to manage the broader thermal network.

Halpern suggests the city may eventually require a different delivery structure should the system expand beyond a pilot phase.“Cities are really good at building projects one at a time,” Halpern says. “They're not always set up to build programs.” Larger buildouts could ultimately involve models that include a public-private partnership.

Denver's approach differs from many legacy steam systems in older cities, Halpern says. Many established systems in cities such as New York, Boston, Washington, Detroit and Chicago draw on rivers and other large nearby bodies of water as reservoirs of thermal energy, giving them capacity Denver lacks. “Even when it's 40 degrees or colder in the middle of winter, there's still a lot of heat mass,” Halpern says. “We don't have that.”

Denver's hot, dry summers and cold winters create different design conditions than coastal cities, he adds, forcing planners to account for larger temperature swings without those natural advantages. Those constraints pushed the city toward a multisource approach built around geothermal and wastewater heat recovery.

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ENR Mountain States & Southwest, Best Project, Energy/Industrial: National Western Center

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Sewer Heat Recovery Meets Downtown Construction Constraints

An early test case was the 250-acre redevelopment of Denver's historic National Western Stock Show campus, an ENR Best Project in 2023, which included what project participants describe as North America's largest sewer heat-recovery system.

The district energy system began operating in 2022 and now supplies approximately 90% of heating and cooling needs for seven buildings totaling more than 1 million sq ft, while retaining capacity for future expansion.

A 72-in.-dia sewer line, known as the Delgany Interceptor, forms the backbone of the wastewater heat-recovery system, connecting to a 25-ft-deep wet well that transfers thermal energy to a clean-water ambient distribution network. U.S. Engineering Construction, which worked on National Western, says crews installed cooling towers, chillers, boilers and multiple 100-horsepower pumps, along with prefabricated piping systems, including 32-in.-dia steel piping integrated into the district loop.

Off-site prefabrication helped accelerate installation of 30-in.-dia carbon-steel piping, ductwork and equipment. Five pump skids—each integrating pumps, piping and accessories and weighing as much as 30,000 lb—were fabricated off-site before final connections were completed at the utility plant.

Project teams also encountered inaccurate civil as-builts and accelerated utility sequencing, requiring redesign and multiple concrete pours to maintain tolerances and avoid delays.

Blair Wisdom, director of energy at Metro Water Recovery, says the downtown pilot will use a substantially different approach from National Western.

National Western relied on what Metro calls an ex-situ, or diversion, system in which wastewater is routed from the interceptor into a wet well and pumping system, then returned to the wastewater network after thermal exchange. Instead, downtown Denver will rely on inline, or in-situ, heat exchangers installed directly within existing sewer infrastructure.

“In this case we don't need to build a separate wet well and pumping infrastructure,” Wisdom says. “We can just capture the heat in place.”

Wisdom says the approach reduces infrastructure footprint and better matches pilot-scale demand while avoiding pretreatment equipment, wet-well construction and other infrastructure requirements identified in the feasibility study.

Construction would still require work inside active sewer infrastructure. “We're going to be draining our pipe, so we bypass pumping, and then we'll be installing the heat exchangers into the pipe network,” Wisdom says. Crews would access the system through existing manholes. “Most of the work happens in the interceptor,” Wisdom adds. “We really do get to kind of better manage.”

Wisdom says National Western benefited from conditions downtown projects rarely have. “[National Western] was a major redevelopment effort,” she adds. Downtown integration, by contrast, means working within “one of the most densely populated parts of the city.”

Metro Water Recovery expects its portion of the system to require relatively limited maintenance once installed. Sensors would monitor system temperatures and thermal load. “We'll know the temperatures, so we can know kind of the thermal load,” she says. “These systems are pretty maintenance-free besides the instrumentation.”

Wisdom adds that the utility is already thinking beyond the initial pilot, considering whether wastewater thermal systems could eventually play a larger role in reshaping Denver's existing energy infrastructure. It's evaluating whether thermal energy captured at its facilities could eventually support decarbonization of Denver's broader district steam network. “Really, this is kind of the first step,” she says.