Denver’s climate office launched a $4.9 million pilot program funded by the state to use water instead of electricity to reduce the use of natural gas for heating and cooling in five million square feet of municipal buildings.

The effort comes amid the city and the state’s pursuit of decarbonization goals, even as officials acknowledged that electrification of large buildings in Denver would be “prohibitively expensive.”

State policymakers have begun to seriously consider geothermal energy in their pursuit of decarbonization goals. Geothermal energy is widely used across the globe. In absolute terms, the U.S. is among its biggest producers, though per capita, other countries, such as Iceland the Philippines, use more.

Only 0.4% of America’s electricity is generated by geothermal energy.

Under Democratic control of the state Capitol, Colorado is seeking to quickly transition away from fossil-fired energy. Supporters argued the transition — while acknowledging it might be painful in the short term — positions Colorado for a more sustainable and energy-efficient future. They said it would help wean the country from dependence on foreign oil. Ultimately, they added, the transition toward green energy is good for the environment and people’s health.

Critics maintained the quick transition is failing to protect American consumers, particularly low-income residents, who already contend with soaring inflation, and that the singular focus on alternative energy is short-sighted, given that America is rich in all forms of energy and that nuclear power can provide the state with a viable, sustainable and “green” baseline.

In the past few weeks, Colorado added nuclear to the list of “clean” sources, alongside wind, solar and geothermal, a move that signaled policymakers’ changing attitude toward this energy source and the realization — some said — that “renewable” sources are insufficient to provide sustainable and affordable energy and at the same time meet Democrats’ carbonization goals.

The city’s Office of Climate Action, Sustainability and Resiliency will use the award from Colorado Energy Office to study a multi-source district thermal water system to provide heating and cooling through a shared water loop for 14 city buildings comprising 5.5 million square feet currently served by Xcel Energy’s downtown steam and chilled water loops.

“Previous studies have explained the major challenges for both the building owners and Public Service — that is, electrification via electric resistance boilers or air-source heat pumps would be prohibitively expensive due to the costs to upgrade the electrical infrastructure within and serving the building,” said Senior Energy Project Manager Drew Halpern in testimony before the Colorado Public Utilities Commission. “Therefore, the city has continued to explore more cost-effective and achievable solutions to this challenge, including scoping a pilot project in our city-owned facilities — a multisource ambient temperature district thermal system.”

By converting the chilled water system to an ambient temperature system that uses both deep geothermal wells and heat from the sewer system, the building’s systems can be converted to water-to-water heat pumps for heating and cooling.

In the winter, the loop would operate at higher temperatures, and in the summer, lower temps, with the option of adding chilled water to help balance cooling loads.

The hybrid system would use about 500 geothermal wells drilled to a depth of 1,200 feet, distributed across seven locations, sewer heat recovery and supplemental heat pump chillers for temperature regulation. It would include renovation of the old Cherokee Boiler Plant to serve as a central utility plant.

“From our analysis, we project an immediate 83% reduction in GHG (green house gas) emissions after conversion to an ambient loop,” said Halpern.

This will substantially reduce both electrical loads and natural gas for heating and will avoid the expense and difficulty of installing greater electrical capacity in the downtown core that would be required for full building electrification, city officials said.

“The city sees this approach as the only practical path to achieving full, or even close-to-full, decarbonization of the downtown building stock without a near-complete rebuild of the electric grid alongside corresponding buildout of generation, transmission, and other necessary infrastructure that comes with its own substantial GHG emissions toll,” Halpern added.

The project estimated saving 80 million gallons of water per year by shutting down Xcel’s downtown steam loop.

“This figure balloons to an incredible estimated 1.4 billion gallons per year when expanded to the entire current steam system,” said Halpern.