Capturing heat from unconventional places is becoming more and more popular as we come to realize all of the many heat sources around us. One such source could provide buildings with a steady, uh, stream of heat: sewage. Philadelphia company NovaThermal Energy is pioneering a technology called sewage geothermal that can tap a city's sewage lines to capture heat for heating and cooling buildings.
The technology, which was developed in Tianjin, China by Jin Da Di Energy Engineering & Technology Co., uses pipes to connect into sewer lines and divert some wastewater flow into a heat exchanger. Wastewater gets its heat from the obvious warm biomatter it contains, but also from dishwashers, showers and industrial processes that send hot water down the drain. In Philadelphia, the wastewater stays at about 60 degrees in the winter and can reach 75 degrees in the summer, temperatures that can heat buildings in the winter and help cool them in the summer.
The system avoids clogs by filtering the water of larger debris before it goes through the heat pump. A device called the "Anti-Block Machine" automatically sprays the water against a screen to prevent buildup of any filth material. You can see the full process in the diagram below.
The system has already been installed in several buildings in China and is currently installed in a pilot project at Philadelphia's Southeast Wastewater Treatment Plant, where the plant's 20,000-square-foot compressor building is fully heated and cooled by the system. That installation was paid for by a $150,000 federal stimulus grant and should pay for itself within eight years. NovaThermal says full-scale projects will pay for themselves even more quickly.
NovaThermal will install a commercial-sized plant at another wastewater treatment facility in Camden, Pa. later this year and then plans to market the system to any large buildings that are near a major sewage trunk line that carries a steady stream of wastewater.