Rockwell Automation Controls Power at Ann Arbor Water Treatment Plant |

Rockwell Automation Controls Power at Ann Arbor Water Treatment Plant

Rockwell Automation power monitoring equipment helps facility reduce energy consumption by up to 10 percent.

With state and local budgets shrinking, and the cost of electricity rising, municipalities need to shave utility costs wherever they can. As major energy consumers, water treatment plants are a natural place to start.

Operators at the water treatment plant in Ann Arbor, Mich., developed a strategy to help significantly lower the electric bill with a simple solution – monitoring and controlling power use to avoid the high charges that come with operation during peak demand times.

Every day, the Ann Arbor plant processes an average of 14 to 15 million gallons of water, and distributes it to 25,000 homes and businesses in the city and beyond. The treatment process is highly complicated because of the water’s source.

“Our plant is one of the most complex in the state because of the quality of our source water, which primarily comes from the Huron River,” said Brian Steglitz, the plant’s senior utilities engineer.

While flow through the plant is primarily by gravity, there are two locations where low head pumps are required to drive the flow though the remainder of the plant’s treatment processes. In addition, the plant uses two large pumps to backwash the 26 multimedia filters that are used to polish the water. These pumps, along with the high service pumps that deliver water to several portions of the city, consume the largest quantity of energy at the treatment plant. The next largest energy demand is exhibited by the plant’s ozone system which uses energy to convert liquid oxygen to ozone for disinfection.

Like managers at most water treatment facilities, those at the Ann Arbor plant routinely paid the electric bill without scrutinizing the individual charges included.

When looking to cut costs, they took a closer look at the plant’s monthly bills and realized that they were paying thousands of dollars in peak energy charges that could potentially be avoided.

“The plant was being hit with high electrical-demand charges – accounting for more than half of its energy bill,” Steglitz said. “Our team knew we needed to find ways to stop throwing money down the drain.”

To manage costs, managers needed to know exactly how much energy they were using – and when – to avoid peak-demand charges. The first step was to understand the rate structure of the plant’s electricity supplier.

Like many energy providers, the local provider for the Ann Arbor plant has different rate structures for different customers. Major energy users, like the water treatment plant, pay more for electricity during peak hours of 11 a.m. to 7 p.m. If they exceed their predetermined allotment for peak-demand energy use, they must pay additional “demand” charges.

Those charges can add up quickly. For example, if operators run the backwash pump for just30 minutes during peak hours, the demand charges could total as much as $4,000.

“Operators needed real-time data to show them when they were approaching electrical peaks, so they could avoid nonessential tasks that would impact our demand charges,” Stegliz said.

The Ann Arbor plant invested in four power monitors to keep a watchful eye on its four substations and transfer energy-use data to the operator’s computers. Unfortunately, the original power monitors were “rudimentary” Steglitz said, and the components were failing.

The situation prompted plant managers to turn to Rockwell Automation, the provider of their existing control platform. “Our history with Rockwell Automation products has shown they are extremely reliable,” Steglitz said. “And when it comes to delivering clean and safe water, reliability is critical.” Ann Arbor invested in Rockwell Software RSPower Plus software and four Allen- Bradley PowerMonitor devices with Ethernet, which connect the devices to the process control network. Data on electrical usage is then communicated to the SCADA system, which displays real-time electrical usage information, allowing operators to make decisions that optimize energy usage. For instance, operators can postpone noncritical pumping and delay backwashing the filter until nonpeak hours.

The system also alerts operators when the plant is approaching peak limits, allowing them to quickly react and ramp down electrical usage wherever possible.

The investment in the PowerMonitor devices quickly paid off . Steglitz estimates the Ann Arbor treatment plant saves between $30,000 and $40,000 per year by precisely tracking and controlling its energy consumption.

Steglitz expects these types of savings to increase as energy intensive water treatment technologies become more commonplace. “Water treatment processes are becoming more energy intensive,” Steglitz said, referring to the advent of disinfection methods using ozone and ultra-violet light, as well as the expanding use of reverse osmosis and other membrane technologies.

Steglitz suggested that many other municipalities could save on energy expenses – and become more sustainable – by adopting the monitoring solution that the city of Ann Arbor implemented. “Saving money is not the only benefit. Conserving energy is simply the right thing to do.”

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