Launch Slideshow

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Power of the Pump

Power of the Pump

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    South Windsor, Conn.'s Veterans Memorial Pool Park, known by locals as the “Spring Pond,” includes three public pools. To save energy, more than 1 million gallons of pool water are filtered according to use rather than 24/7. Photos: Brian Robinson, FlowTech Inc.

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    By retrofitting its pool's three-phase pump system with electrical controls, the South Windsor (Conn.) Public Works Department saved $7,000 on energy bills in one season.

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    The above kilowatt readings show energy usage of South Windsor's pool filter pumps during a seven-day period after the town's public works department installed variable-frequency drives (VFDs) to control motor speed. The upper right portion, labeled “VFDs in bypass,” simulates the power consumption level prior to VFD installation. Source: Brian Robinson, FlowTech Inc.

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    Custom-controlled costs

They took out the existing flow system, installed the bypass and new drive, and had the pump rewired and running within the same day. Although the installation process for all four pumps was scheduled for two weeks, it took only three days.

After installation, maintenance staff set pump speeds using the VFDs' onboard time clocks that initiate preprogrammed, preset speeds. They programmed the pumps to run at 90% power during open pool hours, and to ramp down to 60% overnight. By the end of the pool season, the settings reduced energy consumption by more than 65,000 kilowatt-hours — saving more than $7,000 in operational costs.

BEYOND ENERGY SAVINGS

In addition to lowering electricity bills, the drives also minimize noise. “Now we can actually stand in the pump house and hear each other talk. Before, we were never able to do that,” says Friend.

The drives also enable pool engineers to eliminate hard stops and starts during maintenance. For example, when pool strainers need to be cleaned, engineers ramp the motors down, shut them off, perform the necessary tasks, and then ramp the speed back up — all without across-the-line surges from hard stops and starts.

The drives protect the pumps and motors from over-current and undercurrent by automatically shutting down the system if problems occur, instead of allowing the motors to spin themselves into the ground.

“A major problem occurs when our pumps lose prime,” explains Bruce Lundie, facilities mechanic with the water pollution control division. Prime is lost either when too much air enters the system or when obstructions restrict water flow, causing pumps to stop circulating water. “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.”

When a pump runs dry, it can overheat and become damaged.

“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 to shut down the pump,” says Lundie.

But with the new drives in place, an ABB technician used the company's Drives WindowLite software program to develop “user load curves” as a preventive safety measure. These user-defined adjustable load curves detect underload conditions so drives can automatically shut down pumps when prime is lost. To set the load curves, Friend's maintenance staff determined the amperage draw when the pumps lose prime, padded the number a little, and programmed the drives to trip on a fault whenever that low amperage limit is reached.

AN ECONOMICAL SOLUTION

In all, it cost $28,000 to update the pool's pump control system. The project was partially funded by an $11,000 CL&P energy conservation grant, with the division providing its own labor and materials, saving nearly $10,000 in labor and installation fees.

Friend anticipates recouping all or most of the cost of the upgrade by the end of the 2008 operating season, which ends this month. “Between the energy we're saving and the state energy grant, we're thinking the retrofit will have paid for itself. This is by far the best decision we could have made.”

This chart compares energy usage at full pumping speed to usage with variable-frequency drives (VFDs). In 2007, South Windsor paid about $9/kilowatt to power four pumps at its swimming pool complex.Source: Brian Robinson, FlowTech Inc.