Pennsylvania wastewater plant uses data loggers to measure motor efficiency
In keeping with a national effort to increase the energy efficiency of wastewater treatment facilities, a Pennsylvania plant has used data loggers to analyze motor usage - a first step toward reducing energy costs and meeting environmental regulations.
Upper Allen Township conducted a review of motor run times on existing equipment at its wastewater facilities using data loggers from HOBO, a Massachusetts-based company. The goal was to gather information that would help the plant select new technologies and processes that would reduce energy consumption and nutrient flow.
This article explains why the Cumberland County Wastewater Plant decided to improve its efficiency and how its contractor, Reynolds Energy Services, used data loggers to gather preliminary information.
The importance of modernization
The decision to improve the plant's efficiency reflects a national movement to reduce consumption at energy-hungry wastewater facilities. After labor costs, energy is the largest expense at the 15,000 publicly owned wastewater treatment plants that serve about 70% of the U.S. population, according to the Consortium for Energy Efficiency (CEE). The plants can account for up to 35% of some communities' energy consumption.
As a result, several cities and towns are redirecting funds from the American Recovery and Reinvestment Act (ARRA) to improve wastewater treatment. Upper Allen Township applied for a portion of the $2.2 million in ARRA funds that Cumberland County received, but was unable to secure funds due to the overwhelming number of funding requests the county received.
In addition to reducing energy consumption, the planned improvements at Upper Allen Township's Grantham Wastewater Treatment Plant will help meet federal standards to protect the Chesapeake Bay. The Upper Allen Township wastewater system, located about two hours west of Philadelphia, treats an average of between 500,000 and 700,000 gallons of wastewater daily. The treatment plant was last expanded and modernized in 1990 and uses a Sequencing Batch Reactor (Aqua SBR) system with aerobic digesters. The plant is scheduled to undergo additional upgrades in 2010-11 to meet anticipated new NPDES discharge requirements associated with the Chesapeake Bay Tributary Strategy.
Cumberland County streams flow into the Susquehanna River, which in turn flows into the Chesapeake Bay. The river is considered a major source of nitrogen, phosphorus and sediment to the Bay. For this reason, the US Environmental Protection Agency has developed a "pollutant diet" for the bay. To that end, Pennsylvania wastewater treatment plants must limit their nutrient discharge into the Susquehanna's tributaries in order to receive approval when their permits come up for renewal.
Data loggers uncover inefficiencies
Studies estimate that there is the potential to reduce energy consumption at U.S. wastewater facilities by 15% to 30%. The extent of the savings depends on the size, type, technology and regional operating conditions of the plant. Motor replacement could reduce energy consumption by about 2%, while process control modifications could reduce consumption by 30%, according to CEE.
The aeration process, which uses fans and motors, consumes the most energy. Maximizing efficiency in the aeration process is especially important because it is a peak load operation, which means the plant consumes large amounts of electricity when electricity prices are at their highest. Reynolds Energy Services of Harrisburg conducted a detailed review of the Upper Allen facility with the goal of installing improved aeration technologies that would reduce energy consumption and meet environmental permitting requirements.
Equipment doesn't always operate as efficiently as manufacturers estimate, for a variety of reasons. So the inspectors attached HOBO® U9 Motor On/Off data loggers to existing equipment at the treatment plant and pump stations to "see how the equipment was actually performing," said Michael Conchilla, project development manager at Reynolds.
The project focused on motor loads, particularly on the larger equipment - aerators and pumps at the pump stations. "We had a dozen different motors in logging. We were looking for runtime patterns and how many hours a day they were being used. Many of the motors run on/off, on/off in short intervals. We wanted to see what those patterns were, what the accumulated hours were and extrapolate that to a year," he said.
Reynolds left the data loggers on site for about four weeks. This was easy to do as the loggers are portable and robust standalone devices that work independently of other equipment or connections. The data loggers monitor the alternating field generated by the motors.
"I have achieved excellent results by connecting the loggers to the supply lines in electrical cabinets rather than just using them on the motors. Some of the motor enclosures were too large to get a good field measurement. I will probably do this more often in the future," said Conchilla.
Once the data loggers were retrieved, Reynolds downloaded the information and visualized and analyzed the data using HOBOware® software, which allows for quick readout and display of information and export to spreadsheets.
"We needed to understand the runtime patterns for each individual engine. If you can extrapolate that to a year, you know how many kilowatt hours each motor uses," said Conchilla. "The council regularly collects amperage readings. These are used to estimate the electrical access to the motors. We use that data and the runtime data to estimate the actual kilowatt-hour consumption for each motor."
He added: "As long as you have the amperage data and the runtime, you can do the calculation. We used Microsoft Excel to do these calculations. I would export all the runtime data from HOBOware into an Excel file, tabulate the hours based on the time period and extrapolate that to the year."
Reynolds will use the information to help Upper Allen determine where upgrades to the system are needed and where expenses can be avoided. After the new equipment is installed, the energy services company will continue to use data loggers to confirm the results, a must since Reynolds operates under a performance contract for energy services.
Thanks to the data loggers, Upper Allen can now move forward with its efficiency improvements, safe in the knowledge that any guesswork has been eliminated. "You can't second-guess the data. They tell you what's happening 24 hours a day," Conchilla said.