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Seattle pilot project uses the sewer to warm office buildings

By Conrad Swanson, The Seattle Times
Published: October 22, 2023, 6:00am

Everybody poops.

And when you do — really, whenever you use a toilet, bath, shower or sink — you’re releasing heat into the sewer beneath your feet.

King County wastewater officials announced their first partnership with a private developer to capture that heat, save energy and cut greenhouse gas emissions in the process.

The technology isn’t new. It’s used all over Asia, Europe and Canada — and it works, said Erika Kinno, research and policy project manager for the county’s wastewater treatment division. But this pilot project between the county and private developers is among the first of its kind in the United States, she said.

The partnership is also a first step to expanding the technology throughout Seattle, targeting one of Washington’s largest sources of emissions: large buildings.

In all, four buildings under construction in South Lake Union for Alexandria Real Estate Equities will share a series of underground pipes, tied together by a heat exchange. The system works similarly to a heat pump, gathering warmth from the sewage system and transferring it indoors or, during warmer months, running in reverse to keep temperatures low.

The technology’s official name is “sewer heat recovery.”

Much of the inner workings are already in place three floors underground at 701 Dexter Ave. N. at the east end of a parking garage.

Aboveground the concrete foundations are beginning to take shape for what will become an 11-story building with penthouses and research space.

Once operational, that fairly innocuous mass of tubes and shiny metal coverings will connect that building with three others — 601 Dexter Ave. N., 816 W. Mercer St. and 714 W. Mercer St. — which will all make up the Alexandria Center for Life Sciences — South Lake Union.

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County spokesperson Alison Hawkes said the system should be running by 2025.

The whole campus will boast more than 1.6 million square feet of space, said Hart Cole, Alexandria’s senior vice president and strategic market director, as he and a team of developers, engineers and others unveiled the system Tuesday for King County officials and news media. The sewer heat recovery system will be able to handle up to 70% of the whole campus’s heating and cooling needs.

There are four basic steps in the process, said Michael Hedrick, a principal engineer at McKinstry, the Seattle construction and energy firm that worked on the project:

  • The system taps into the main line of King County’s sewer system, drawing in wastewater, which hovers between 65 and 70 degrees.
  • A mechanism (a patented technology by SHARC Energy) separates the solid waste from the usable, warm liquids.
  • The system pumps that wastewater through a heat exchange where the warmth is transferred to clean water.
  • It then pumps that warm, clean water throughout the complex and dumps the cooled wastewater back into the sewer.

“It really is quite elegant in its simplicity,” Hedrick said.

This particular project is unique among others like it because it’s in a dense urban core and because it shows that sewer heat recovery systems can be built by tapping into existing sewer lines that are often decades, perhaps centuries, old, said Jodi Guthrie, global director of sales for SHARC Energy.

That means not only can crews install these energy-efficient heating and cooling systems into new buildings, but they could also retrofit old buildings to use the systems, Guthrie said.

Adapting existing buildings is a critical component to King County’s goal of halving its emissions by 2030, County Executive Dow Constantine said.

Kinno noted that commercial and multifamily buildings — which benefit the most from these systems — produce about 22% of King County’s greenhouse gas emissions.

Constantine said he was impressed with the overview and is eager to see how well the system performs.

But before sewer heat recovery can be used more widely, additional research is needed. The county opened three slots for pilot projects in 2020, Kinno said, and Alexandria’s development in South Lake Union is the first. Two other spots have yet to be filled, she said.

Once two more developments are accepted into the program and up and running for three years, county officials can examine their results and decide whether to expand the project further, Kinno said. Applications are open.

The possibilities for the technology are nearly limitless, county officials and engineers said.

“This literally could change the future of the planet,” Hedrick said.

The U.S. Department of Energy estimates that people flush about 350 billion kilowatt-hours down the drain every year across the country, enough to power about 30 million homes.

The largest sewage heat recovery system in North America is running through a series of buildings in Denver. There, at a complex shared by the National Western Center — which hosts a massive national livestock show every winter — and Colorado State University, the system is running more efficiently than expected, said Brad Buchanan, CEO of the National Western Center.

Four buildings are hooked up to the system now and more are on the way, Buchanan said. The larger the scale, the more efficient the process becomes and it’s already cutting enough carbon emissions to equate to a single gasoline-powered car driving 6.6 million miles every year.

That’s enough to drive around the globe more than 265 times.

Should developments in the future have a large enough scale, enough money for the upfront investment and the proximity to sewage lines, Buchanan said he’d recommend they install a similar system.

“There’s no question this is the right decision,” he said. “It’s the right thing to do and it makes financial sense.”

City officials in Denver are also considering whether to retrofit downtown infrastructure to capture sewer heat, said Emily Gedeon, a spokesperson for Denver’s Office of Climate Action, Sustainability and Resiliency.

That’s the direction King County could go, should the pilot projects prove successful, Kinno said.

“This is a resource that is simply too good to waste,” Kinno said.

Before you ask, Guthrie added that the entire system sits within a closed series of pipes. Perfectly sealed. So, no. It doesn’t smell.

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