ShareThisSewer Power Heats Paris School
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Steel plates containing closed-loop glycol piping are arranged end-to-end along the side of the sewer canal to capture heat. |
A Paris school is benefiting from a modern twist on an old practice. Using heat generated by sewers isn’t a new idea – in fact, sewer heat is used unofficially in many parts of the world. But this pilot implementation offers a simple and promising technique to capture and direct sewer heat for use in warming the building and its 400 pre-K and primary school students.
The new system by utility Lyonnaise des Eaux is called Degres Bleus – Blue Degrees. It launched in April and will meet 70 percent of the building’s annual heating needs. It will save 30,000 euros (US$43,000) per year and eliminate the 76.3 metric tons of carbon emissions that would have resulted from the old natural gas furnace system.
It’s a simple concept – the warm sewer water that circulates through the canals under the metropolis at an average 15° C (59° F) is a “primary material” available 24/7, thanks to still-hot discharges from washing machines and dishwashers.
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A heat pump in the basement concentrates the heat to 140 degrees F. before circulating it to the existing radiator system. |
The heat is captured as the sewer water passes over a network of submerged steel plates containing a closed loop pipe system of glycol water, a heat-conveying liquid. The plates are lined up end-to-end along the walls of the canal so as not to impede water flow. The warmed steel plates heat the glycol over 60 meters of heat exchange piping before sending it to the heat pump in the school basement where the heat is concentrated to 60° C (140° F). The heat pump then circulates the heat through the existing radiators in the school. The old gas furnace is still operational to provide supplementary heat on unusually cold days. See the Degres Bleus technology explainer video.
The heat recovery system is safe, nonpolluting, requires no fuel and only transmits heat. The cost of the system, which includes the installation of a heat pump in the school and heat exchange system in the Coteaux main drain, was 400,000 euros (US$574,000). Half was financed by utilities Lyonnaise des Eaux and CPCU (Compagnie Parisienne de Chauffage Urbain), which will keep the difference in heating costs, and half by ADEME, the French government’s environment and energy agency. The system will pay for itself in about 10 years.
Paris mayor Bertrand Delanoe, who attended the inauguration of the system in April, was impressed. “I believe it’s really intelligent from a sustainable development standpoint,” he said. He added that the city plans to do the same for other sites, including a mayoral branch office, a public gym and public swimming pool, and another school. “And I’ve proposed that we study the feasibility of doing City Hall,” he stated.
According to a spokesperson from Lyonnaise des Eaux, provincial cities are already ahead of him. The Bordeaux and Valenciennes City Halls have already inaugurated such systems.
The technology factors into the city’s climate plan, which calls for 30 percent renewable energy and 30 percent greenhouse gas reduction by 2020. The city estimates that the system could be used by 10 percent of Parisian buildings. The Degres Bleus technique is subject to certain technical limitations, including proximity to a sewer canal that is large enough to maintain a constant flow of water, but is ideal for high heat consumption neighborhoods that could include restaurants and dense residential areas.
See the "language-neutral" technology video about the system
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