At Veterans Memorial Park in South Windsor, Conn., keeping clean more than 1 million gal. of water for three outdoor swimming pools—a 755,000-gal. main pool, a 156,000-gal. training pool, and a 152,000-gal. lap pool—is a demanding, around-the-clock task. High-powered pumps—two 30-hp, 200-v, three-phase pumps for the main pool, a 20-hp, 200-v, three-phase pump for the training pool, and a 10-hp, 200-v, three-phase pump for the lap pool—pull water from the bottom of the pools through a series of gutter systems and into surge tanks. From the surge tanks, the water is pumped through a series of chemical-purification filters and back into the pools.
The electricity required to run the four pumps 24/7 is by far the largest operational expense related to the pools. With tens of thousands of dollars worth of utility costs each season, Tim Friend, plant supervisor, looked for ways to reduce energy consumption without sacrificing water purity.
“We wanted to lower our high power bills,” Friend said. “We knew we were wasting energy via running the pumps at full power—especially after hours. Fewer impurities are in the water when nobody is swimming, so by slowing the flow at night, we knew we could still maintain adequate filtration in the pool and the same levels of water quality.”
INITIAL EFFORTS TO IMPROVE EFFICIENCY
Friend and his team implemented several strategies with limited success. First, they tried shutting off the pumps at night. Water quality became so difficult to maintain the tactic soon was abandoned. Friend and his team then tried throttling the valves. Because the pumps ran on single-speed motors, doing so drove up motor amps, back-flushing equipment.
Friend then turned to Flow Tech Inc., a South Windsor-based HVAC sales and service organization. Working closely with Brian Robinson, Flow Tech sales engineer, Friend concluded that ABB variable-frequency drives (VFDs) could provide major power savings.
“By installing ABB VFDs at the pool, we could reduce the motor speed, but still run our system with the valves completely open, all the while achieving the full flow rate we need to run the filtration systems,” Friend said.
On Flow Tech's recommendation, Friend and his team selected an ABB ACH550 VFD for the 20-hp motor and similar VFDs for the two 30-hp motors and the 10-hp motor. Flow Tech provided bypass panels for the pumps so the pool engineers could bypass the VFDs if the need arose. Flow Tech delivered the drives and bypass panels, and Friend's maintenance staff handled the installation, beginning with the smallest pump first.
“The lap pool was our guinea pig,” Friend said. “Our goal was to demo the existing flow system, install the bypass and VFD, and get it back up and running the same day. Since it was the smallest pump, we had the most physical space with which to work, and we were successful in accomplishing our goal.”
Friend's crew spent a day installing the VFD for the 20-hp pump and another day installing the VFDs for the two 30-hp pumps.
“We were thrilled at how quickly and smoothly the installation process went,” Friend said. “Although we spread it out over a couple of weeks, it was basically only three days worth of work.”
After installation, the speeds of the pumps were set back using on-board time clocks. The pumps are programmed to run at 90-percent power during open-pool hours and to ramp down to 60-percent power for 12 hr after the pools close. Those settings are anticipated to yield an energy-consumption reduction of more than 65,000 kwh per season—and to save more than $7,000 in operational costs annually.
In addition to dramatically lower energy costs, installation of the VFDs has resulted in far less noise from the pumps.
“Now we can actually stand in the pump house and hear each other talk, whereas before, we were never able to do that,” Friend said.
SYSTEM PROTECTION AND ELIMINATION OF HARD STOPS AND STARTS
When maintenance is required, pool engineers can ramp down the motors, shut them off, perform the necessary tasks, and then ramp up the speed, all without high demand and across-the-line surges from hard stops and starts.
The VFDs also protect the pumps and motors from overcurrent and undercurrent, shutting down the system if problems arise.
“A major problem occurs when our pumps lose prime,” Bruce Lundie, facilities mechanic, explained. “We are stepping the speed down at night to save power, so if the strainer baskets become clogged with leaves or debris, we could essentially not draw enough vacuum from the pump. This happened to us before where we lost prime during the night. We came in the next morning to find the pumps red hot and steam boiling out of the strainer baskets because we had nothing in place to protect the motor or shut down the pump.”
As a preventive-safety measure, an ABB technician, using the Drives WindowLite program, determined the amperage draw when the pumps lost prime, “padded” the number, and programmed the drives to trip on a fault when that low-amperage limit is reached.
With the energy savings the park is experiencing, Friend anticipates recouping the cost of the VFDs and their installation in two seasons.
“We don't have the final numbers back from this season yet, but between the energy we are saving and State of Connecticut energy grants, we're thinking the retrofit will have paid for itself by the end of next year,” Friend said. “This is by far the best decision we could have made.”
For his role in providing efficient and cost-saving solutions for the community, Robinson was awarded the 2007 South Windsor Public Works Business Partnership Award.
Friend is looking at ways to incorporate ABB VFDs on other projects, including a major water-treatment-plant renovation.
“I'm so pleased with ABB VFDs that I'm specifying the rest of the treatment-plant upgrades around incorporating them,” Friend said. “We've had nothing but top-notch results from the drives in every experience.”
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