Denver is building a sewage-powered thermal energy network

Denver is planning to build a thermal energy network to power a group of downtown buildings in a defunct boiler house, reports Ishan Thakore for NPR.

The project will use heat from wastewater to power heating and cooling mechanisms for buildings that currently rely on "the world's oldest continuously operating commercial steam system," a steam network that runs on natural gas. The city will repurpose parts of the system in an "ambient loop" for 11 city-owned buildings using circulated water and heat pumps. 

"The city estimates it will cost roughly $280 million to $320 million to build out the network over the next decade, though it says those costs may fall. The pilot is being funded by a combination of city dollars and a state grant." The project is still roughly 75% less expensive than other options for decarbonizing the same buildings, according to a feasibility report. Geothermal energy, once the infrastructure is in place, is essentially free, and the city plans to use "sewer heat recovery" to harness heat from wastewater to bring down other energy costs.

Denver officials hope to eventually expand the network, tapping into the essentially limitless heat of the earth.