The use of advanced engineering tools in HVAC industry has increased as the cost of computational fluid dynamics (CFD) has become more affordable for engineering firms. A thermal storage tank system utilized a series of vertical tanks to store chilled water and supplement chillers in the event of a power failure. Chilled water is routed from the storage tanks to critical equipment during chiller re-start@ bridging the gap in time that the chillers are unable to provide set-point chilled water due to power failure and subsequent required time to re-start. The main challenge of the tank sizing was to optimize the tanks in order to maximize the output time of stored chilled water while minimizing the height and quantity of the tanks. The goal was achieved through an innovative design in which the tank diffusers were designed through a series of simulations. Once installed@ the system was tested rigorously to the same conditions that were previously simulated during design. The result of field-testing verified that the CFD model was accurate within two percent margin of error. Utilization of this process allowed the design-build team to save installation time@ money@ materials@ and building square footage by reducing the number of required storage tanks to provide the required stored chilled water quantity.