King County’s South Treatment Plant (South Plant) recently underwent a heart transplant operation. It was complex because South Plant doesn’t just have one heart, it has six. Raw sewage pumps are the heart of a treatment plant, providing the power to move wastewater into the plant. Skilled teams replaced three of the six pumps and developed new ways to operate them to make them as energy efficient as possible.
Water is heavy, and moving it around takes a lot of energy. King County’s Wastewater Treatment Division (WTD) is responsible for 54 percent of total energy use for all King County facilities, so even small energy savings make a big difference. The pumps are vital to plant operations and vital to energy efficiency, and after 50 years of service, it was time for three pumps to be replaced.
While the pumps were reliable and easy to operate throughout their lifespan, they were also inefficient. These pumps liked to take it slow and steady, like power walkers on a level surface. Because people use the most water in the morning and evening, flows into the plant vary. Just like a power walker, the pumps have to work harder when the terrain gets steep. The pumps can throttle up and down as flows vary, but this wastes energy as heat. Since energy efficiency was a primary objective for the project team, they enlisted the WTD energy team to get involved.
King County Wastewater’s Energy Program strives to reduce energy consumption, increase energy efficiency, and maximize the creation and use of renewables. They work to help project teams find ways to improve operations.
At first, the project scope was limited to replacing three of the pumps, but the project team discovered they could do more than simply replace the pumps with new ones. They could use better, more energy efficient technology and equipment, such as new drives, motors and switchgear. The project team also generated significant savings by installing more energy efficient heating, ventilating and air conditioning (HVAC) equipment, as well as developed a complex construction sequence strategy which resulted in further savings by eliminating the need for a new building to house the new equipment. Finally, not only were energy savings realized, the project came in under budget and a whole six months ahead of schedule.
Thanks to the energy savings, King County had an opportunity to secure grants to fund some of this project. Puget Sound Energy (PSE) has different types of energy efficiency grants. King County purchases some of the electricity needed to run the raw sewage pumps from PSE. Customers like King County contribute a percentage of their energy bill to fund energy efficiency grants that the customer can apply for. For the Wastewater Treatment Division, that means almost $1 million over five years.
The new pumps and motors were more energy efficient on their own, but most of the energy efficiency comes from the controls – the drives. According to the Project Manager, variable frequency drives are much more energy efficient because they allow you to “match the right amount of energy for the speed that you want.” The variable frequency drives are more like runners than power walkers. They are conditioned to maximize their energy efficiency and to be able to start and stop quickly, which saves energy. The engineers for the project also selected the most appropriate pumps to best match the variable flow conditions which also contributed to the energy savings.
But it took a new strategy and plan to get the three new pumps working efficiently with the three remaining pumps and the energy team was there to help create it. The team knew WTD could receive almost $1 million in PSE energy grants for this project, but only if the new pumps and their variable frequency drives met certain performance standards. When the engineers visited the operations shift supervisors in the control room, they knew what was coming. The new pumps, motors and drives needed a different operations plan, or WTD would only be eligible for part of the PSE grant funding.
In order to report performance, the team needed to collect good data during the wet season when flows and energy use vary with storms. Thanks to help from South Plant Operations staff, the team was able to collect the right energy data. Then Plant staff put their faith in a strategy the team proposed, even though it was different from their usual protocol. The new strategy worked: it minimized electricity use and guaranteed maximum return on the PSE grant. The team’s willingness to try different things and find the best solution was key to maximizing efficiency of the new pumps, motors and drives.
In October 2017, the project team received word they earned a grant award of $894,970 from PSE, the largest single utility grant King County has ever received. Puget Sound Energy estimated that this project will save 1.9 million kilowatt hours per year, which is the same amount of electricity required to power 212 homes. Saving energy and increased energy efficiency also saves money – almost $4 million over the next 20 years.
“WTD deals with energy the same way you do at home, only on a much larger scale,” said Division Director Mark Isaacson. “Similar to how you install energy efficient appliances or wash your clothes with cold water, WTD selects equipment that will be energy efficient and runs that equipment the best way possible. This is just one way we take simple actions to lower our carbon emissions and contribute to the future of our community.”
More than 100 employees dedicated over 30,000 hours on this project to give the raw sewage pumps a new, energy efficient life and to help South Plant’s most vital systems running. This project was exceptional in that WTD engineers prepared the design rather than hiring outside consultants. This resulted in close coordination with all involved, especially with Plant staff which was critical to the project’s success.