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Take a second to get past the yuck factor and then consider this: As much as 40 percent to 50 percent of a building’s energy is contained in sewage and literally goes down the drain every day. When the water we heat for cooking, cleaning, bathing and washing our clothes, among other uses, enters a sewer system, it helps to heat the wastewater flowing through the underground sewer systems to an average temperature of 60 F to 80 F. It creates a stable, flowing geothermal source of energy that until now — in the U.S., at least — we’ve been, well, wasting.
What if we could recover some of that wasted energy, recycling it back into our buildings for heating in the winter and cooling in the summer? Well, we can and starting this year, we will be doing it in our nation’s capital at the DC Water’s new state-of-the-green-art headquarters on the banks of the Anacostia River in southeast Washington.
SmithGroup, as part of a design/build team led by Skanska USA, was selected in 2014 to design the new 150,000-sq.-ft. headquarters. To meet DC Water’s aggressive sustainability goals, the team knew they had to look not only at the most advanced technologies available in the United States but also at innovative technologies that were best-in-class around the world. We wanted, in short, to push the outside of the LEED Platinum envelope.
A major challenge at the outset was a requirement that the new office structure be built on top of DC Waters’ existing O Street pumping station and adjacent to the historic pumping station. These two facilities could not be shut down during construction; they pumped 45 million gallons of sewage a day from the nation’s capital to the Blue Plains wastewater treatment plant.
Overcoming this challenge required us to approach the problem not as an obstacle but an opportunity. Could we find a way to incorporate a historic, century-old infrastructure into the design as an asset to help leverage 21st-century energy- and water-efficiency goals?
SmithGroup found the answer by looking to the Old Country — Europe, which has been ahead of our curve in pioneering and deploying technologies to capture and re-use expended energy. This is technology tested and proven across much of Europe, parts of Asia and, more recently, in Canada. However, due to the burdens of our regulatory system, it only recently received its green card to emigrate to the U.S. But it is a comparatively simple and cost-effective technology whose time has come.
There are two types of Sewage Wastewater Energy Exchange (SWEE) technology used around the world to do this: in-line systems with underground energy exchange piping systems and offline systems using pumped wastewater and above-ground heat exchangers.
The process is similar in both cases. Raw sewage passes through a separator or screening system, which removes solid waste and sends it back to the sewer. The liquid waste then passes through a heat exchanger, which extracts its thermal energy to heat a separate stream of clean fluid. The heat-depleted wastewater returns to the sewer, while a heat pump distributes the clean fluid throughout a building in much the same way as a conventional boiler or radiator system works.
Because the sewer piping infrastructure already existed on site for the new DC Water headquarters, an in-line system was not possible. However, there already was a large wet well at the O Street pump station that could be incorporated into an offline system. From that point, we focused our design on finding the best international manufacturer of an offline sewage wastewater energy exchange systems, which turned out for our project to be Canadian manufacturer SHARC Energy, Vancouver, B.C.
Researching New Technology
While SWEE technology has a demonstrated record of success in Europe and Canada, any innovation applied for the first time in any locale requires that you first do your own due diligence to understand how it can be applied. In late 2014, when we started our homework, we found there were two primary manufacturers of offline sanitary wastewater energy exchange systems to choose from — Huber in Germany and International Wastewater Systems (now renamed SHARC Energy) in Canada.
Both systems achieve the same end but differ slightly in how they do it. SHARC uses a patented screened augur system to separate solid from liquid waste and a plate-and-frame heat exchanger to extract thermal energy from the latter, while Huber uses a screening and settling system for separation and a shell-and-tube exchanger for heat extraction.
We further vetted the SHARC technology on a trip to Canada to inspect manufacturing processes and quality control at SHARC Energy’s headquarters. We toured existing installations and talked directly with plant engineers and operators about the reliability of their systems and the maintenance requirements. Our tour included visits to three of the first operating SWEE systems in North America.
The SAIL condominium project in Vancouver at the University of British Columbia, which captures waste heat from a multifamily residential project to generate domestic hot water. In operation since early 2014, this domestic hot water SHARC Energy project has proven to be one of the most cost-effective heating systems to deploy commercially.
The Gateway Theatre Project in Richmond, B.C., which uses a SHARC system to draw wastewater from a lift station to create an ambient heating loop that, depending on the time of year, heats or cools a 50,000 sq.-ft. multiuse theater. Installed in 2013, the system has eliminated the need for both a cooling tower and the use of fossil-fuel-fired boilers for supplemental heat. In its first full year of operation, it lowered the theater’s fuel costs by $15,000 and its greenhouse gas emissions by 70 tons.
The Southeast False Creek Energy Center, built in 2010 to provide all the heating for the Olympic Village at the 2010 Winter Olympics in Vancouver. Although not a SHARC installation, it is an example of one of the first district-scale installations of SWEE systems in the world.
Based on SmithGroup’s research into the technology and the first-hand findings gathered on the trips, we felt confident the SHARC system’s reliability and economy would help DC Water realize its ambition of not only meeting the strict standards of LEED Platinum certification but pushing well beyond them.
Any building can tap into this energy flowing through city sewer mains with the cooperation of the local wastewater utility agency. Every million gallons of wastewater has the potential to produce a megawatt of cooling for a building. In a city like Washington, producing on average 200 million gallons per day, the cooling potential is 200 megawatts — enough to cool 18.5 million sq. ft. of office space.
Moreover, cooling that office space with SWEE would save nearly 250,000 metric tons of CO2 emissions annually (equivalent to a whopping 54,347 cars removed from the road). If you look at the heating potential in colder climates, the environmental benefits skyrocket.
Clearly, mining the energy that flows just beneath our feet is a major step forward in green building technology and could make significant improvements in the environment.