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Sewage Heat Recovery

Posted by Lynn Mueller on May 10, 2016
Sewage Heat Recovery
SHARC Sewage Heat Recovery installation.

Environmental awareness is spreading across countries like a slow, yet steady, fire. Enterprises that focus on energy saving schemes are constantly on the lookout for fresh ideas. Nearly every second day, a new project is charted out in some part of the world. Some of them fail due to lack of funding, while others collapse because of their irrational basis. Only once in a while, an idea that is conceived actually makes it into the real world. One such idea is that of sewage heat recovery.

What does the concept of sewage heat recovery involve?

A lot of hot water is washed down the drains in the average American home. Everyday activities like taking baths or showers, dishwashing, cooking, or doing the laundry, use up hot water that enters a complex or condo. Most of it is wasted away, exiting the building at nearly the same temperature it was heated up to. Sewage heat recovery projects aim to trap the heat flushed out along with wastewater, and use it to heat water entering the building.

How does the typical sewage heat recovery system work?

The design is simple. The very step involves redirecting the wastewater so that it doesn’t leave the building. The solids in the incoming sewage water are winnowed out, and the filtered water that remains is passed through a heat pump or exchanger. This is where the heat is stripped out of the wastewater, and used to heat fresh water entering the building.

How viable is this idea?

In a word: very. To elaborate further, we’ll have to look at the numbers. Generally, water entering a condo is around 5 to 7 degrees Celsius, while water leaving it is 20 to 25 degrees Celsius. Taking into account the statistics in the US alone, we find that energy worth around 40 billion dollars is flushed down the pipes. Of this, it is possible to recover close to 35 billion dollars worth of energy, with the help of a functioning sewage recovery system. As a condo owner, or a hotel manager, you’re probably aware of the huge costs that go towards monthly or annual maintenance expenses, and the accompanying electric bills. With the installation of these heat recovery systems, a great portion of these costs can be cut down.

Are there any successful heat recovery projects?

Several such projects have been installed and run successfully. One of the most famous ones is the condominium in Vancouver that is home to 172 units. A sewage heat recovery system popularly known as the SHARC system has been installed in this condo, and is running efficiently. Another condo comprising of 60 units, also in Vancouver, managed to achieve a reduction of up to 75 percent in the energy used to heat water entering the units. This condo went on to receive a LEED platinum rating.

What are the primary challenges?

One of the hardest parts of employing a heat recovery system is to ensure that is functions smoothly over the long term. The SHARC system has managed to achieve the right solution to this setback by operating with a coefficient of performance of around 5, and an energy efficiency ratio of over 20. The coefficient of performance is measured as the ratio of the power output to the power input, while the energy efficiency ratio is measured as the ratio of the output cooling energy to the input electrical energy. In simple terms, the ideal heat recovery systems should seek to offer a reasonable amount of output energy per unit of input energy, in order to operate over a longer period.

Another test that needs to be aced is to fight the stigma associated with recovering heat from sewage. Understandably, most people find the idea repulsive. However, there is no cause for concern because the solids are filtered out long before the heat is extracted. Once these hurdles are crossed, heat recovery systems can be installed in hotels, shopping malls, large schools and commercial complexes just as successfully as they are in condominiums.

How financially viable is the system?

This is typically measured in terms of return on the initial investment. While it does take considerable funding to set up a SHARC system, the average period taken to earn the return on investment ranges from 3 to 7 years for a standalone sewer heat recovery system. However, when a geothermal system is integrated into the setup, the return on investment is as good as immediate. As a rule, the larger the condo, and the more units it accommodates, the sooner the return on investment can be obtained.

From the perspective of a regular condo owner, installing a system that recovers the heat that is flushed out is one of the most cost effective alternate sources of energy. An added bonus is that the emission of carbon dioxide and other accompanying greenhouse gases is reduced greatly.

 

Lynn Mueller is President of International Wastewater Systems, Vancouver, British Columbia. Lynn has been a leading advocate of sustainable space conditioning energy systems for the last 25 years. He was the President of WaterFurnace Canada, following that he was the President of Earth Source Energy Inc. 

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