Using Sewage to Provide Buildings’ Heating, Cooling

Sewage: it’s the ultimate renewable energy source, says International Wastewater Systems (IWS) founder and CEO Lynn Mueller, who has commercialized a wastewater heat recovery process that captures heat from sewage and provides buildings’ heating and cooling.

For every 10,000 people, 1 million gallons of 70 degree Fahrenheit sewage is created per day. According to the US Department of Energy, 400 billion kilowatts of hot water goes down the drain annually in the United States, which is roughly 40 billion dollars’ worth of energy at an average cost of $.10/kW.

Sewage is free, it’s abundant, and it’s widely untapped.

“Traditionally all that hot water would have left the building, gone down the drain and been lost forever,” Mueller said in an interview. “We like to refer to this as the ultimate renewable energy source because you use it, it goes down the drain and you use it again the next day,”

At IWS’ largest residential installation to date, the 172-unit Sail condos by Adera Development Corp. at the University British Columbia, its SHARC system provides hot water for all of the units at about 550 percent efficiency. This saves residents about 70 percent on their hot water heating bills. It also reduces emissions by about 100 metric tons per year, IWS says.

The Sewage SHARC (SHARC stands for sewage heat recovery) uses raw sewage to produce hot water, heat and cooling for multi-residential, commercial and district energy systems. The technology separates the solids from the wastewater and extracts heat via a heat exchanger to produce up to 160 degree Fahrenheit water for potable use, all before the wastewater is sent to a treatment plant.

Mueller says the SHARC system costs about $400,000 more than a traditional system and has a five- to seven-year payback. It’s completely sealed so there is no smell. With regular maintenance it will last between 30 and 40 years, he says.

In addition to the custom-built SHARC, IWS also makes the Piranha, a prepackaged unit designed for 50-200 unit residential buildings and stand-alone commercial applications.

Mueller says the company has installed a dozen of its wastewater heat recovery systems in multi-unit residential, industrial and public buildings in the US, Canada and the UK, and has between 50 and 60 new projects “on the drawing board.”

Its next planned installation is Wall Centre Central Park in Camden, New Jersey, by Wall Financial Corporation. IWS’ SHARC will serve as the primary domestic hot water heating source in the condo and townhouse development. The building was designed to meet LEED Gold standards — which is another benefit of the system, Mueller says. In addition to the emissions reductions, energy savings and primary energy cost reduction, which is usually between 30 percent and 85 percent, IWS’ systems can earn builders LEED points for sustainable building design.

Mueller says IWS’ wastewater heat recovery can be counted as a base load power source because it can generate consistent, reliable power to meet demand: “It’s not like solar, where you have to worry if it’s a cloudy day. Sewage is a resource you can count on.”

Brent Giles, research director at Lux Research who leads the firm’s water and E&P practices, says a wastewater heat recovery system like this makes sense for larger multi-family and commercial buildings.

“It’s the right direction to go,” Giles says. “We need to think about how to get value out of waste streams. We need a robust discussion about not just water reuse, but heat reuse.”