Texas Utility Tests Technology to Trim Energy Use at Water Treatment Plants
Originally published July-August 2013
Because making the water we use clean is an extremely energy-intensive process, Georgetown Utility Systems in Texas tested a new technology with the capacity to limit the energy used at its water treatment plant on Lake Georgetown.
With support from a grant from the Demonstration of in Energy & Efficiency Developments (DEED) program, the Georgetown utility installed a dynamic pump optimizer, or DPO, on its plant intake pump controls, which provide water to the Lake Georgetown Water Treatment Plant that serves 30,000 residents. A DPO is a controller that instructs the pumping system to change its speed, enabling it to save energy while still meeting required demand for water. This was accomplished by connecting the DPO to the variable frequency drives controlling water-pumping speed. Engineering firm Steger Bizzell developed the DPO and also prepared the final DEED report on the demonstration project.
With the DPO installed, the utility measured specific energy consumption, defined as the amount of energy required to move a unit of water from the lake through the entire treatment process. Specific energy consumption “captures all energy losses in the system: inefficiencies in variable frequency drives, motors, and pumps, pipe friction losses, minor losses, and changes in static head,” according to the final report prepared by Steger Bizzell,
In addition to saving energy, running at minimum specific energy consumption speeds “puts less strain on pumps and motors,” extending pump and motor life and reducing maintenance costs. The DEED project, however, focused only on measuring energy-efficiency gains.
Promising Technology Has Greater Potential
Georgetown compared data logged over several months with the DPO installed against historical flow and energy-use information. With the DPO, the plant experienced a 5 percent reduction in energy used—less than anticipated by the utility. The utility also tested the technology at five additional sites (without DEED funding), where savings ranged from 3 percent to 28 percent.
Although the utility concluded that minimizing specific energy consumption provided “clear economic benefit to water pumping stations,” with energy reductions translating directly into cost savings, it also determined that a more nuanced technology would be needed to maximize savings.
At the Georgetown Water Treatment Plant, the presence of possible siltation, tuberculation or filamentous bacteria growth in the pipes adversely affected the water flow. Additionally, flow data from previous years were difficult to estimate largely due to fluctuations in the level of Georgetown Lake, which could not be accounted for in the calculated savings.
“The project has demonstrated the need for a more sophisticated type of control,” says the final report. “The more sophisticated controller will honor any constraints imposed by the particular system, but will always operate at the most efficient point, given those constraints.”
New Technology Keeping Pumps Healthy
That new control, developed by the company Specific Energy, was rolled out at the Texas Water Convention in Galveston, Texas, in April. In addition to saving utilities more energy than the DPO model tested by Georgetown, the new DPO focuses on alerting operators when pumps become worn and, therefore, inefficient. According to Steger Bizzell, the new technology will not only help to reduce utilities’ environmental footprint, but also help them meet the growing demand for energy-efficiency standards.
“The potential market for minimizing specific energy consumption is large,” the report said. Potential savings in the United States could exceed 9 billion kilowatt-hours per year, Steger Bizell said. Worldwide savings could exceed 91 billion kilowatt-hours, the company said.
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