via Globe and Mail
Monday, December 30, 2013
By Richard Blackwell
The warm water being flushed down Canada’s sewers could become a huge source of recycled energy.
Wastewater heat is already being put to use in a handful of buildings in British Columbia, where a small company called International Wastewater Systems is on the leading edge of the technology and hoping to turn it into a formidable business.
IWS’s system takes heat from the water going down the drain from sinks and toilets in a condo, and transfers it to the clean water coming into the building. It can dramatically cut water heating costs, and thus pay back the price of installation within a couple of years.
The system works because wastewater is consistently at about 20 to 25 degrees Celsius. With heat exchangers, that energy can be used to generate hot water at higher temperatures.
IWS founder and president Lynn Mueller, who trained as a refrigeration mechanic, said he was working with geothermal heating systems when he began considering all the warm water which was being flushed down the drain.
“I was thinking that every day I comfortably flush down water that it cost me $10 or $20 a day [to heat],” he said. “That is perfectly good heat.”
A 2005 U.S. Department of Energy study estimated that 350 billion kilowatt-hours of heat energy is flushed down the drains in the United States each year.
The key to Mr. Mueller’s system is the special filter his company designed, which temporarily removes the solids from the wastewater, leaving it just clean enough to pass through a heat pump without clogging the heat exchangers. The warmth from the wastewater is transferred to a flow of fresh water – without either stream of water coming in contact with each other. The solids are then combined back into the wastewater before it goes down the sewer.
The system also has software that monitors it at all times – “a brain that reports to us before any problem exists,” Mr. Mueller said.