Why Flow Was an Issue
he plant presently includes a 192- tank thermal ice storage system that goes into action during peak usage hours to provide cooling to all of its on- line facilities between the hours of 11:30AM to 9PM during summer operation. Three high-efficiency, 1200 ton centrifugal chillers are dedicated to the ice storage system alone. Three other 1200 ton centrifugal chillers produce chilled water to satisfy off-peak requirements, with variable frequency drives adding to overall efficiency. When expansions are complete, the thermal storage system will include a total of 236 tanks, making it one of the largest thermal storage systems in the United States. T
The diversity and the sprawling layout of the property presented definite flow control challenges. Prior to the centralized chiller plant, and during its implementation, the staff had struggled with low T (temperature change) issues – where cooler-than-desired return chilled water was flowing back to the chiller plant due to the numerous 3-way valves at various air handling units throughout the site.
According to John Trowbridge, P.E., Project Development Engineer at Shell Point, balancing any additional structures, such as the new medical center, would have been very costly, burdensome, and questionable in accuracy since the chilled water pumps were already in operation serving a much larger facility. All of the air handling units for all of the buildings would require rebalancing at the same time.
This, along with the high differential pressures found in some areas of the
property, made Belimo Pressure Independent Characterized Control ValvesTM (PICCV) an ideal selection for the air handlers throughout the system.
The PICCV combines a differential pressure regulator with a two-way control valve and actuator for electronic flow control. The pressure regulator controls the amount of flow passing through the valve according to the change in pressure. All pressure changes are absorbed by the pressure regulator allowing the differential to be held constant over the control valve section, thereby providing consistent flow. This is different from conventional 2-way control valves, whose operation can be severely
distorted by system pressure changes. “The PICCV’s circumvented the issues we had and we now have a self-balancing system for the Med Center,” says
Trowbridge. “Because proper chilled water balancing is in force for the Med Center, we are assured that the T across the coils is at design conditions, working optimally, and any additional pumping energy required for the Med Center is minimized.”
A 192-tank thermal ice storage system helps Shell Point avoid costly peak energy requirements during the cooling season. The chiller plant makes and stores ice during off-peak hours at night and then uses the stored capacity to deliver all its required cooling between the hours of 11:30AM and 9PM. The system helped earn Shell Point one of the largest total rebates in Florida Power & Light history.
Higher Close-off Pressure Means Greater Reliability
ecause the PICCV has a very high close-off pressure rating, it can easily close off against the higher pressures found at some of the air handlers on the property, making it every bit as reliable as globe valves in many applications, often at a fraction of the installed cost. B
Even so, Dan Parker, a seasoned veteran in chilled water systems, was prepared for
certain flow issues to crop up when the first PICCV controlled system, the Shell Point medical center, went on-line. He was pleasantly surprised.
“There was no impact on the system whatsoever. No increases in flow, chilled water demand, or pump power,” said Parker, adding that since start-up, no manual balancing has been required at the medical center, thanks to the dynamic system balancing the PICCV provides.
Approximately 40 PICCV valves are installed in the Shell Point medical center, with more planned for current and future construction projects. It's one less thing to worry about for Dan Parker, his staff, and Electronic Systems Services, Inc. of Ft. Myers,
the controls contractor on the project.
The PICCV valves are but one (albeit significant) feature of this showcase plant,
which has already been toured and studied by engineers, service technicians and suppliers from all over the United States. The attention is well deserved. The facility’s state-of-the-art thermal ice storage system has earned it one of the largest total rebates ever from Florida Power & Light (FP&L). With two more miles of piping to go, and several new construction projects underway, the facility
will undoubtedly continue making chilled water history in one of the country’s toughest-to-cool climates.