The town of Sechelt, British Columbia, Canada, had a problem. For decades, the town had ejected all of its residents’ untreated sewage directly into the waters of the Sechelt Inlet. In addition to clashing with the Sunshine Coast’s general eco-friendly culture (Sechelt is just two hours from Vancouver, British Columbia, which plans to make itself the “greenest” city in the world), Canada’s Wastewater Systems Effluent Regulations published in July 2012 made the practice illegal. So, the town’s leaders decided to not just build a sewage treatment plant, but a state-of-the art facility.
“They wanted to set an example to the world,” says Lynn Mueller, CEO of International Water Systems (IWS).
In Sechelt’s quest to set that example, the town’s leaders chose a bid that included hydroponic water cleansing and a SHARC system from IWS. The latter allowed the facility to use its single most renewable resource (wastewater) to minimize the energy required to heat the facility.
Why Recover Heat From Wastewater?
Architects and engineers have scoured building designs for ways to save heat—thicker insulation, white roofs, double-paned and tinted glass—but their efforts have had a glaring blind spot: wastewater. The Department of Energy estimates that Americans and Canadians wash 400 billion kW of hot water down the drain each year. At an average energy cost of $0.10 per kW, that’s $40 billion annually—and that figure leaves aside more subtle ways that water leaches heat out of homes and workplaces. Water in pipes and toilets enters cool and absorbs heat out of the air over the course of hours.
While environmentalists have identified wastewater as a source of energy loss, efforts to mitigate that energy loss have generally been confined to using less water. Low-flow toilets, high-efficiency laundry machines, and graywater reclamation systems all help reduce the need for water, but they do nothing to capture the heat leaving with the water still used.
Until recently, few people have considered ways in which they might recover that lost heat, but the process used by the SHARC rests on a fairly simple and reliable principle of physics.
What Is the SHARC?
On average, wastewater tends to settle in a consistent range of temperatures around 70°F, according to Mueller and materials from IWS. The SHARC lets building owners and operators transfer that heat to water entering the heat or hot water system. This raises the temperature of the incoming water and reduces the energy required to get it up to its desired heat level.
“We take the black water. We take a mixture of the shower, laundry, that kind of water, mixed with the toilet water through the SHARC,” says Mueller. The SHARC filters and separates the black water. Solids and particulate travel back to the wastewater holding tank. The remaining warm water flows into a heat exchanger. The heat exchanger operates on the second law of thermodynamics to allow the heat from the wastewater to infuse the incoming water.
Mueller noted that this infusion does not include the smell from the black water. The SHARC water is hermetically sealed, he says, and the black water and the heating water “are four systems apart by the time the heat moves back into the tank.”
“I don’t think anyone moving into a building would even know that they’re getting their heat from wastewater,” he added. Once the SHARC warms the incoming heating water, secondary systems boost its temperature as needed.
Design Challenges
In the case of Sechelt’s wastewater treatment plant, the consultants and contractors working with IWS had an abundant source of wastewater to work with, but they were also heating an unusual building.
Sechelt’s wastewater treatment plant—aiming at the cutting edge—includes a greenhouse. The plants’ roots grow down into the water and suck up toxins.
While this solution is novel, it introduces an energy challenge. Average low temperatures in Vancouver hover between 33 and 38°F for five months out of the year, and the treatment plant’s heating system must keep greenhouse temperatures around 70°F at all times.
Fortunately, as a wastewater treatment plant, the facility was at no lack for ambient heat to sap. The facility’s designers positioned a 250,000-gallon holding tank near a mechanical room, which became home to the SHARC system.
More Than Water
While holding tanks and heat exchangers form the core of the IWS SHARC system, the company also employs digital assistance and long-term planning to optimize its system.
“There’s a whole strategy as to how to use it efficiently that we’re experts at,” says Mueller.
That strategy rests heavily on predictive analytics. The practice uses past data and computer models to predict likely future needs, and has permeated many corners of municipal, industrial, and facility management over the past decade.
In the case of IWS’s wastewater heat recovery systems, this means knowing and automating how much wastewater to leave idle in the tank during periods of low activity so that it can be available during periods of high need.
The SHARC software also uses incoming data to predict upcoming maintenance needs. By watching the efficiency of each component at all times, the computer systems at the Sechelt wastewater treatment plant can alert staff when a component has fallen out of its optimal range. This enables maintenance workers to make big repairs in a timely fashion, and to perform minor maintenance that can head off long-term problems.
“We want to design the building so that it absolutely operates at the peak efficiency all the time,” says Mueller.
While predictive analytics help keep the system in line from day to day, its long-term efficiency starts during the planning stage. Mueller says his company worked with Vancouver-based Urban Systems to help design the plant—and this collaboration began before the company won Sechelt’s design contest for the facility.
Easy Maintenance
While understanding the science behind the IWS heat recovery system might require a Ph.D. (thermodynamics remains a perennially daunting corner of physics), the system’s maintenance doesn’t.
Workers at Sechelt’s plant don’t have to worry about maintaining the tanks’ insulation, because the tanks don’t require it.
“That’s one of the beauties of it, you don’t need to insulate the tanks particularly,” says Mueller. “It’s virtually ambient room temperature . . . It’s a very friendly building system.”
The SHARC system requires annual maintenance, but IWS designed it to allow workers easy access to the most frequently changed parts. Workers loosen the bolts at the top of the chamber in the center of the unit, remove the cap, and find the filter inside.
The SHARC also includes a computer interface that allows the maintenance crew to quickly and easily view operational information—such as average temperatures for the past 90 days—through a touch-screen. Facility managers can also export the system’s readout and controls to a computer, website, or mobile device.
Long-Term Investment
For the town of Sechelt, the SHARC system at their wastewater treatment plant represented a long-term play. The system’s installation cost about $300,000—roughly triple what a modern, efficient oil or gas system would have cost. But it could save the town more than a million dollars over the facility’s lifespan.
Mueller estimated the plant’s annual energy savings at $30,000–$40,000. At that rate, he says, the system would pay for itself in five to six years.
Once the SHARC completes its payback period, it will continue to pay dividends.
“It’ll run for 40 years without fail because nothing is going to change that’s going to make this thing outdated.”
A Sign of Things to Come?
Mueller makes a bold prediction about wastewater heat recovery systems. In five years, he expects building codes to require them. That prediction is especially bold because IWS only started making the SHARC six years ago, and governments have so far shown little support for them. Mueller says he was unaware of any subsidies for wastewater heat recovery in the US or Canada (though he did know of some in Europe).
But Mueller says he expects quick adoption of the technology for two reasons: One, it’s relatively cheap and easy. Two, the December 2015 Paris Accords will push developed powers around the globe to get their environmental house in order.
Sewage heat recovery may represent a solid tool for that. His SHARC systems, he says, range between 400% and 600% energy efficiency. For every 100 kWh a customer uses to power one of these systems, they save between 400 and 600 kWh.
“We like to think of ourselves as the ultimate renewable energy,” says Mueller. “We use the same energy day after day after day.”
Mueller also expects to see more large-scale installations for sewage heat recovery. His company recently helped convert the Borders College campus to a hybrid sewage heat recovery and natural gas system. Once the college completed the project, it held an unveiling event attended by Canada’s minister of energy.
But many developers may not need a regulatory push to install wastewater heat recovery systems. With guaranteed long-term savings and a way to earn difficult-to-claim LEED points, progressive developers are already giving the SHARC a close look.
“We’ve had people from all over the world literally come to Sechelt to see the sewage heat recovery option,” says Mueller.
