When setting up the study, the group confronted a snag: Commercial pools in Texas are to be outfitted with NSF-approved equipment, but there were no commercial-grade pumps with such approval. But the standard was silent about adding variable-frequency drives to existing single-speed pumps, despite addressing variable-speed pumps with onboard controls.
The group considered adding external variable-speed control drives to the existing pumps. While city officials believed that likely would nullify the NSF certification on those pumps, the concern was addressed by working with NSF staff to write Annex P, Variable-Speed Pumps Recommendation for Installation and Operation. In addition, the experts decided to retrofit pumps with variable-speed pump controls tied to paddle wheel digital flow meters to monitor and regulate flow rates. This was meant to ensure mandated turnover and optimize chemical dispersion and water clarity regardless of increases to total dynamic head (TDH) resulting from filter loading and other factors.
Certain conditions needed to be in place for any individual pool to be considered for a retrofit. Most importantly, the circulation system’s ability to move water had to exceed flow rates needed for proper turnover. Otherwise, there would be no wiggle room for reducing pump speeds. This didn’t rely solely on the pump’s power, however. Surplus flow could be gained by improving hydraulics through smaller measures that would reduce TDH, or resistance, within the system.
To indicate which pools would qualify, the team assessed more than four years’ worth of data on each unit’s age, dimensions, flow rates, pump and motor information, filter types and energy consumption. This would show trends over multiple swim seasons and help staff project the energy-savings potential.
The players also conducted energy and hydraulics audits on each pool, recording such factors as power used, total dynamic head and pressure on the suction and pressure sides of the system.
During this process, the team could pinpoint hydraulic conditions hampering turnover flow rates. Two primary factors were observed. First, they evaluated the effectiveness of filter backwashing practices, in terms of frequency and how well the system was set up. They looked for problems that could undermine the needed backward flow rates, such as undersized pumps, inoperable or leaking backwash valves, and backwash waste lines incapable of handling the minimum flow rate. Secondly, they checked for factors that would restrict flow, such as undersized pipes and filters, air vacuum leaks that could cause pump cavitation, and improperly adjusted or missing bypass valves on heaters.
The team determined that 22 of the 26 pools could be retrofitted. City staff would be trained on how to properly operate the equipment during the study period.
After installing variable-speed technology and making hydraulic tweaks, they conducted another audit and inspection to project energy savings and water quality.
Performance was audited with a clean filter, and under simulated dirty-filter conditions, achieved by throttling a valve to cause a 10- to 15-psi rise in pressure, in an effort to understand when the pump performance did not match the pump curve.
While the pools were being studied, city staff temporarily changed how they monitored the water. Rather than checking quality three times a day as had been the norm, they began checking it hourly.
“So as soon as the filter had a problem or a chlorinator wasn’t feeding, they were finding that out quickly,” Barnes says.