Project Update

AGU Seeks International Best Practices for Sewer Heat Exchange

By March 29, 2017 No Comments

By Greta Perry, MGAC, and Samantha Patke, Interface Engineering

Over the course of the design process for AGU’s headquarters renovation, the project team explored more than 40 different individual engineering strategies. A project exactly like ours has never been done before, and we determined early in the process that a custom bundle of strategies would need to be developed to address AGU’s specific goals and needs. The team landed on 26 strategies that, when combined, would help AGU achieve their goal of net zero energy.

During our exploratory phase, it became evident that geothermal energy was not a viable option due to a lack of sufficient land to accommodate the number of required wells and a limited clearance in the building’s garage. Our team from Interface Engineering was forced to explore alternate strategies, and landed on using a municipal heat exchange system that takes advantage of a very large combination storm and sanitary sewer main located directly outside AGU’s front door – which was built in the 1890s and lies 30 feet below Florida Avenue. The closed loop system is designed to pull water from the sewer through a heat exchanger and return it back into the sewer system.

Our first task was to learn as much about these types of systems as possible. With only an handful of similar systems in North America, and no HUBER Technologies installations specifically, we would need to look outside the country to see a fully functioning system firsthand.

In coordination with DC Water – whose approval will be required prior to the implementation – we identified a German manufacturer with several HUBER installations in Germany and Switzerland and booked our trip. A diverse team of representatives from AGU, MGAC, DC Water, Interface Engineering, Skanska and U.S. distributor Havtech traveled in late February to visit the HUBER Technologies factory in Berching, Germany, and several of their working installations.

The project team at HUBER Technologies in Germany.

The project team at HUBER Technologies in Germany.

Site Tour 1: Straubing, Germany – Public Housing Project

The first stop on our tour after the factory tour was a public housing project located in Straubing, an independent city in south Germany. The first installation of the HUBER RoWin heat exchanger in Germany, the 102-apartment complex is home to two RoWins – one for heating and hot water for apartments, and a second for redundancy. The system’s wet well is located down the street from the housing complex and connects to the city’s main sewer line as it feeds into the water treatment plant. The installation was also the most similar in size to what is planned for the AGU project.

Site Tour 2: St. Gallen, Switzerland – Halg Building

The Halg Building is made up of 50,000-square-feet of office space, and 17,000-square-feet of HVAC shop and production. The mechanical systems are almost identical to those planned for AGU and have been in operation for the past three years. The sewer water is supplied int
o a remote wet well located about 160 yards from the building. The screened waste water is then pumped from the wet well to the basement of the building to the RoWin heat exchanger. The building utilizes radiant cooling panels and radiant floor heating, and ventilation for the building is provided by an energy recovery DOAS unit.

Site Tour 3: Winterthur, Switzerland – WinTower Office Building

Located northeast of Zurich, the WinTower is a 236,000-square-foot office building. Standing in the wet well that supports the building, we saw the potential of this system realized. The 28-story office building is about twice the size of AGU’s building and has been in operation for six years. The WinTower system consists of two submergible pumps in the wet well that pumps 800 gallons per minute (GPM) of wastewater to two RoWin heat exchangers in the basement mechanical room. The wastewater heat exchange system provides both heating and cooling to the building.

How It Will Work for AGU

  • Wastewater is brought via gravity into the wet well.
  • Wastewater is screened of its solid materials, and the screened wastewater is then pumped into the building.
  • Wastewater is pumped into the RoWin heat exchanger tank.
  • Condenser water fills the tubes inside the heat exchanger tank and transfers heat without coming into direct contact with one another.
  • Condenser water is then pumped to a chiller.
  • Finally, the wastewater is returned to the sewer system.

Through this trip, and in close collaboration with DC Water, our team has developed a way to safely tap into the sewer flow and take advantage of free cooling for a portion of the year. As a bonus, this strategy also eliminates the need for rooftop cooling towers, which will drastically reduce the project’s water usage.

We came away from our trip confident in the technology’s reliability and efficiency, and are excited to introduce a new way to leverage sustainable strategies by being the first to install this system in the U.S.