Posted on September 30th, 2012

Outside the Box – Sewers and Geothermal Energy

Do you ever wonder where the energy from the hot water you use to wash clothes or take a shower goes? The water runoff obviously goes to a treatment plant, and the energy (heat) goes with it, making the sewers a very warm place. Consequently, cities around the world are looking into tapping into this potential source of energy.

In 2010, Hidden Fuels, a Brainerd, Minnesota based company installed sensors in the city’s sewer system to gauge temperature levels for a one-year period. Their findings showed that there was enough energy to heat hundreds of homes in Brainerd. The company’s next step is to convert this energy into a usable resource, which while difficult, is not impossible. The idea is to use a heat pump to circulate water and use the energy to heat or cool buildings. The Director of Buildings and Grounds for Brainerd’s Public School says there is enough energy stored in the pipes to heat the high school in the coldest months, which costs $18,000 a month on average.

But Brainerd isn’t the only city giving this idea some thought, Paris, France is as well. Under the streets of Paris are approximately 1,500 miles of sewer pipes, and the temperature is fairly consistently maintained at 68 degrees. Currently, Parisians pump a heat-transferring liquid into their sewers which has been effective in providing geothermal-based energy for 10% of the city’s needs. An obstacle they are trying to overcome is the distance that geothermal energy can be effective; as right now, Paris is only able to generate energy for edifices within a 600-foot reach.

Philadelphia-based NovaThermal Energy is also working on a technology called sewage geothermal which uses pipes to connect into sewers and diverts wastewater into a heat exchanger. The wastewater in Philadelphia maintains a temperature range from 60-75 degrees, depending on the season. The system is currently being used in several buildings in China, and is also being used as a pilot-project in Philadelphia’s Southeast Wastewater Treatment Plant. The installation in Philadelphia costs about $150,000 which was supplied by a federal stimulus grant and should pay for itself in eight years.


novathermal

Above is a diagram of the NovaThermal Energy’s system for wastewater treatment. The Anti-Block Machine automatically sprays the water against a filter to prevent buildup.

Canada is in the game as well. Renewable Resource Recovery Corporation (R3C) out of Ontario used their technology to heat a 2,000 sq. ft. home for the entire winter using only their source-energy pipe system. This is quite impressive as Canadian winters can be frigidly cold – with the coldest days never getting out of the teens. In their system, geothermal wastewater pipes are installed in the ground and are connected to a heat pump distribution system in a home’s basement. Heat is extracted from the soil and wastewater, and then recycled into the home’s heat distribution system.


r3c

The R3C system is designed to be used on a single home and can provide year-round comfort for each establishment’s residents.

The benefits for this system could be far-reaching. Greenhouse gas emissions would be drastically cut as there would be no carbon dioxide emissions from a furnace or fireplace. The energy equivalent for the R3C system would be that of removing three cars from the road. Geothermal heat recovery systems are 500-times more efficient than a standard gas or electric furnace. Currently, the R3C design is a comparable cost to that of traditional heating and cooling systems, though their piping is more costly. But this is clearly a technology on the rise, and outside the box. If the trend continues, look for cleaner, more efficient heating and cooling in the future!

Justin Harmon

Staff Writer

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