This 54,000 ton-hour chilled water thermal energy storage system is an "empty tank" concept with six equal size underground chilled water storage tanks. The tanks are located beneath an intramural athletic field that has been restored to its original purpose. The system supplements a chilled water central plant of 18,000 tons, most of which was designed by LSW. Water is moved in or out (charging or discharging) via variable speed pumps thereby providing a variable charging or discharging rate. System pressure is maintained by automatic back pressure valves. A sophisticated control system anticipates loads and stored capacity to optimize the storage strategy.
The system was designed to shift 6,800 kW from peak summer demand. During the first two months of winter operation, a cost savings of $168,000 was realized by the University. These savings came from a 4,600 kW demand shift, which will increase during summer operation. It is currently saving taxpayers over $1 million per year. Project total cost of approximately $5 million ($92/ton-hour), coupled with a utility company incentive payment of $875,000, yields a net cost of $4.2 million ($76/ton-hour) for a simple payback of 3.4 years.
LSW was responsible for performing a feasibility study that established the TES design parameters and automation controls, and provided full system commissioning. We helped Arizona Public Service Company determine ASU's incentive payment, life cycle costs and payback periods with various TES options. Structural Engineering for the empty tank design was included in the LSW responsibility, which included a 5.5 million gallon tank, 3' below grade, and coated with waterproofing to achieve water tightness.
Owner: Arizona State University
Size: 54,000-Ton Hour Chilled Water TES System
Construction Cost: $5,000,000