Field-measured performance of four full-scale cylindrical stratified chilled-water thermal storage tanks

Results are presented for controlled flow rate tests in four full-scale cylindrical chilled-water storage tanks. The tanks range in volume from 1.15 to 5.18 million gallons (4.35 to 19.61 million liters) and have water depths of 40 to 65 ft (12.2 to 19.8 m). Water is introduced into and withdrawn from two of these tanks using radial parallel plate diffusers, while the remaining two tanks utilize octagonal slotted pipe diffuser designs. Thermal performance is quantified for full cycles in terms of Figure of Merit, for single charge and discharge processes as half-cycle Figure of Merit, and for incomplete charge and discharge processes as Lost Capacity. Results show that the thermal performance of all four tanks is excellent, with less than 4% of theoretical cooling capacity lost to inlet mixing and other degradation mechanisms for flow rates less than or equal to design. Based on these results, the appropriateness of current design guidance is discussed. Operational issues that affect implementation of controlled flow rate full-scale tests are also identified, and measurement issues are addressed.