By Paul Miller, Contributing Editor
The Veterans Memorial Pool Park In the town of South Windsor, Conn., is a much-loved summer hotspot for children and adults. Once merely a pond, the local swimmin hole evolved into a full-fledged aquatics center over the years. The modernization of the current complex was completed in the spring of 2002. It houses three separate outdoor swimming pools: a training pool for children; a lap pool; and the main pool. The pools stay open from the first weekend in June until the last weekend in August, attracting an average of 600-800 visitors per day during the hottest months.
The high cost of keeping the pool water clean
While the pools themselves are a relaxing escape for members of the community, keeping the more than one million gallons of water used in the three pools clean is a demanding, round-the-clock task. This falls upon the shoulders of the same busy Public Works Department staff that also operates the towns municipal wastewater treatment plant. The water in all three pools must be continuously circulated through a system of purification filters. High-powered pumps maintain a continuous flow through the elaborate system of water purification filters. These pumps pull water from the bottom of the pool through a series of gutter systems and into surge tanks―one tank per pool. The water is then pumped from the surge tanks through a series of chemical-purification filters before being returned to the pool.
Actual KW readings taken after installation of the Variable Frequency Drives
The high flow demands require some real horsepower: the 152,000-gallon lap pool draws water through the system using one 10-hp, 200-V, three-phase pump; the 156,000-gallon training pool uses a 20-hp, 200-V, three-phase pump; and the 755,000-gallon main pool uses two 30-hp, 200-V, three-phase pumps.
The electricity required to run these four pumps on a 24/7 basis is by far the pools largest operational expense, and tens of thousands of dollars are budgeted for utility costs each season. As a result, Tim Friend, plant supervisor, is constantly looking for ways to improve efficiency and reduce costs, while still maintaining water purity.
ABB drives added to accommodate varying pumping requirements of pools at Windsor, Conn.
Friend and his team tried implementing several different strategies with limited success. The first strategy was to completely shut off the pumps each night for a specified period of time. This made it so difficult to maintain water quality that they had to abandon the tactic altogether. They then tried throttling the valves to achieve the proper flow rate through the pumps, but since the pumps ran on single-speed motors, doing so also drove up the motor amps, back-flushing the equipment.
Variable-frequency drives help reduce energy costs
Friend then drew on his experience operating water treatment and purification plants, where variable-frequency drives (VFDs) are often used to allow pump motors to be safely operated at reduced speeds. To find the best solution for the pools, he consulted with Brian Robinson, a sales engineer at FlowTech, a local sales and service representative for ABB VFDs. Friend and Robinson had previously worked together on a number of projects.
Brian turned me on to VFDs a long time ago, said Friend. We saw how great they worked in similar applications on several previous projects. By installing VFDs at the pool, we determined that 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.
Charlie Albert, Dave Geng, and Bruce Lundie (left to right) handled the installation of the VFD drives, operating the filtration pumps for the three pools in South Windsor, Conn.
The lap pool was our guinea pig, says Friend. 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 in which to work, and we were successful in accomplishing our goal.
Friends crew then completed installation on the 20-hp pump in a day and spent another day on both 30-hp motors. We were thrilled at how quickly and smoothly the installation process went. Although we spread it out over a couple of weeks, it was basically only three days worth of work.