The redeveloped National Western Center (NWC) in Denver, Colorado, relies on a unique energy source – sewage! U.S. Engineering Construction (USEC) collaborated with the NWC to build a sewer heat recovery system for their District Energy Plant that will serve seven buildings.

How Heat Recovery Systems Work

This ground-breaking, green-energy project employs a SHARC sewer heat recovery system. To produce renewable heating and cooling, sewage is pumped from the Delgany wastewater mains into the NWC District Energy Plant through a wet well and into the SHARC interceptor. Within the interceptor, solids are broken down before going through piping in a heat exchanger. The SHARC system either extracts heat from the sewage supply piping or rejects heat into the sewage return piping. The heat exchanger, paired with large pumps, pipes heating or cooling water from the sewer heat recovery system to the buildings on the NWC campus. The heating and cooling water loop maintains room temperatures in NWC buildings.

With a closed loop, the wastewater never touches the clean heating and cooling water that circulates around the NWC campus. The system at NWC is one of the first SHARC system installations in the United States and the largest in North America, producing 3.8 MW or 13,000 kBtu per hour of energy.

NWC’s Impact

The NWC District Energy Plant sewer heat recovery system relies on raw sewage from area businesses and homes. Wastewater from dishwashers, showers and toilets provides valuable heat, which fuels this innovative system. Recovering heat from these sources generates considerable energy because sewage maintains a consistent temperature throughout the year. Rejecting heat into the sewer systems in the summer months also enables building cooling. In this case, the sewer heat recovery system produces chilled water that is pumped to the NWC campus buildings. This process lowers the cooling load on the District Energy Plant chiller equipment and reduces electricity consumption. As a result, the carbon footprint at the NWC campus is drastically reduced.

The potential impact for this new technology is significant. The U.S. Department of Energy estimates that Americans waste the equivalent of 350 billion kilowatt hours of energy each year through wastewater. If harnessed, this natural resource could heat about 32 million U.S. homes.

Heat recovery systems not only supply energy, but they also mitigate related environmental impacts.  When released into waterways, cleaned wastewater effluent can still elevate water temperatures. The effect can be harmful to fish and aquatic life, especially in the wintertime, when river water is expected to be cold. By extracting heat from the sewage, rivers can maintain normal temperatures, and aquatic life can flourish.

Results

NWC’ s heat recovery system is projected to meet 90 percent of the heating and cooling needs of seven buildings, more than 1 million square feet on this 250-acre campus. The sewer heat recovery systems will prevent an estimated 2,600 metric tons of carbon (CO2) emissions per year. That is the emissions equivalent of driving a gas-powered vehicle 6.6 million miles!

The District Energy Plant

The NWC District Energy Plant also consists of many large pieces of back-up equipment for when the cooling and heating loads exceed the output of the sewer heat recovery system. USEC installed cooling towers, chillers, multiple 100-horsepower pumps and boilers. The District Energy Plant features large-diameter steel piping throughout the building, such as a 32-inch diameter inlet and outlet to the main ambient loop. Because the District Energy Plant is housed in a prefabricated metal building that could not support the weight of these pipes, all piping systems were pre-assembled off-site and mounted on steel I-beam frames that were bolted to the ground. U.S. Engineering Metalworks prefabricated the large diameter pipes at its Johnstown, Colorado, manufacturing facility, where team members also produced the chiller and pump skids off-site.

The building manager planned to remotely operate the plant from Houston, Texas. To accommodate this arrangement, a robust industrial-style DeltaV controls system was installed, allowing for precise remote monitoring and control of the District Energy Plant systems.