Unique closed-loop glycol solar pool heater installed on indoor high school swimming pool
For many commercial aquatic facilities, the most cost-effective BTU for pool heating applications is achieved through the use of unglazed, polymer solar thermal collectors. Inexpensive—yet durable—plastic collectors are mounted downstream from the filtration pump, and utilize pool water as the heat transfer fluid in an open-loop system design. No additional heat exchanger is required, and the pool itself acts as the storage tank. That is, at least, how most unglazed polymer solar pool heaters are designed.
Inevitably, some potential customers will have a different set of requirements when it comes to system design. Such was the case for the 3,000 ft2 indoor swimming pool at the Red Lion Area High School in Red Lion, Pennsylvania. A solar pool heater had been included as part of a larger energy-efficiency program instituted by the school, which was contracted to the Fortune 500 multinational Johnson Controls (York, PA). Installation of the solar heater, which was sub-contracted to Lime Energy Services (Allentown, PA), came pre-engineered with some unusual design specifications, resulting in a system that operates more like a solar domestic water heater.
When using pool water as a heat transfer fluid in most climates, solar heating systems must be installed to drain back to the pool when the system is being bypassed. If water remains in a collector when the solar system is off, it could potentially suffer damage from high pressure or freeze damage. The school, however, did not want to be required to drain or winterize the collector array, so the guide specifications dictated a closed-loop system with a heat exchanger, utilizing a 50/50 Hercules Cryotek 100 propylene glycol/water solution in the polymer collectors instead of pool water.
At 3,072 ft2 of solar surface area, consisting of 64 4’ x 12’ Aquatherm Solar Industries® collectors, the system was sized at just over 100% coverage of the pool. Since the school’s plans strictly prohibited any roof penetrations, 64 collectors were mounted at 0° elevation on a self-ballasted pressure-treated wooden rack, which was built on-site. Two 3 ½ horsepower Pentair Intelliflow pumps piped in parallel provide the necessary 300 GPM flow to and from the collectors through 4” schedule 80 PVC pipe.
The system contains 650 gallons of glycol/water mixture, which circulates past an over sized ITT frame-and-plate heat exchanger with 106 ft2 of surface area. The system is fitted with an Amtrol expansion tank, which is necessary to allow the system to withstand temperatures ranging from -10°F in the winter to 150°F stagnation temperature in the summer (without ever exceeding a system pressure of 30 PSI). According to actual system performance based on monitoring, the system is easily capable of delivering close to 950,000 BTUs per hour to the pool, exceeding even the design calculations originally proposed to the high school.
As Aquatherm’s Regional Distribution Center for the northeast United States, Richard Bonte of Sun Source Energy Products (Netcong, NJ) supplied the solar collectors, Pentair pumps, and Goldline controllers. Bonte also worked closely with the PE to ensure the school’s system would achieve a reasonable balance between cost-effectiveness and BTU collection.