A secret cache of clean energy is lurking in sewers, and there are growing efforts to put it to work in the battle against climate change.
The U.S. Department of Energy estimates Americans wash enough energy down the drain every year to power about 30 million homes. The sources are often everyday items inside homes. Think hot showers, washing machines and sinks. Evolving technology is making it easier to harness that mostly warm water.
Denver is now constructing what is likely the largest sewer heat-recovery project in North America, according to Enwave, a Canadian energy company set to operate the system.
Over the next few years, a $1 billion remodel will turn the 250-acre site, home to the National Western Stock Show and Rodeo, into a hub for art, education and agriculture. The revamped National Western Center will include about a million square feet of new indoor space, all of which will be heated and cooled with energy from the sewer pipes below.
Brad Buchanan, the CEO leading the redevelopment, said the project has already changed how he thinks about the best location for real estate. Big pieces of sewer infrastructure have long repelled development. Now he imagines they might be sought out as a way to save energy costs and avoid greenhouse gas emissions.
The National Western Center estimates the project will help it annually avoid the carbon equivalent of driving an average gas-powered car around the equator 250 times.
“It’ll be interesting to see if folks start to look at not just where light rail lines or good schools are located, but what’s the proximity to a large sanitary sewer line,” Buchanan said.
The technology to harvest sewer heat isn’t complicated.
At the National Western Center, construction crews have already completed a pit exposing the main sewer line. The wastewater inside stays a mild 55 to 75 degrees year-round, local officials say, no matter the weather outside. That consistent temperature can be tapped to heat and cool aboveground buildings.
The key is a massive heat pump, which will be housed in a central plant on the campus. The device works like a reversible air conditioning unit. In the winter, it will transfer energy from the sewage into a clean-water loop connecting the buildings, adding heat to indoor spaces. The process can then be flipped to keep things cool in the summer.
Shanti Pless, a research engineer with the National Renewable Energy Laboratory in Golden, Colo., said the technology opens up a vast world of “renewable heat mining.”