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Brainerd considers using sewage to heat, cool buildings

Scott Sjolund heads up technology for Brainerd Public Utilities. CONRAD WILSON | MPR News 91.3 FM

BRAINERD, Minn. - When people in Brainerd run the dishwater, or take hot showers, they not only use energy, they create it.

The water they use and the waste they flush down toilets all flows to the sewer, which not surprisingly can be a pretty warm place - and heat can generate energy.

Brainerd officials say that unconventional source of energy to heat holds huge energy potential for heating and cooling buildings, likely starting with the city police station and a school building.

Under the right conditions that could save the city, the Brainerd School District and residents money.

"Everybody heats water," said Scott Sjolund, technology supervisor for Brainerd Public Utilities. "That's potential energy that could be extracted."

The idea for the project comes from Brainerd-based Hidden Fuels, a company that has been creating a thermal energy map of the city. In 2009, the company began working with the city and the Brainerd School District to seek a $45,000 grant from the federal stimulus package.

In 2010, a team led by Peter Nelson a principal of Hidden Fuels, installed sensors in the city's sewers. For more than a year they measured the temperature and the amount of sewage running through them.

"It shows that there's a significant amount of energy -- literally enough to heat hundreds of homes within the streets of the city of Brainerd," Nelson said.

That data helped the team match energy sources with buildings where they could install a new heating and cooling system.

Now that officials know how much energy the city creates, the next step is converting it into usable energy, Nelson said. That's challenging, but doable.

Hidden Fuels will rely on technology already in use. Similar to the way geo-thermal heating and cooling systems work, a heat pump will circulate water from which energy can be extracted to heat or cool buildings.

Officials in Canada used a similar system during the Vancouver winter Olympics. But it didn't have the challenges of using an existing sewer. What Nelson and others want to do in Brainerd is new because the water's full of waste.

"We're not dealing with clean fluids," he said. "We're dealing with contaminated fluids. So that's really the challenge, is to be able to operate efficiently in that contaminated environment."

Earl Wolleat, director of buildings and grounds for the Brainerd Public Schools, said there is enough energy running in one of the sewer pipes to heat the high school. In cold months that can cost around $18,000.

"If you stop and think about it, it's not surprising that the energy is there," Wolleat said. "But I think it all comes down to the practical application ... to find that way to get that heat out of the sewer."

Wolleat said he's confident Hidden Fuels can pull it off, but it will take years before it's cost effective for the district.

"Right now with the cost of energy being so low, I don't see anything on the horizon right away where it would be an advantage to us," he said. "It's definitely going to be an advantage to the district over time, but with the price of natural gas right now, not so."

Those low energy prices are a roadblock for many alternative and renewable energy projects. However they may become more attractive if fossil fuel prices rise.