District Energy - 2008 4th Quarter

management team quickly decided against the ice TES system, citing that it would require a change in the existing refrigeration system to produce the ice, either through a chiller replacement or addition. The team also preferred the simplicity of a stratified chilled-water system’s operation, which would require very little maintenance. While ice storage systems need less space than chilled-water storage systems, both would raise concerns about tank location; however, since USC was not limited by space – given that the tank would be buried – priority was placed on ease of operation.

In November 2002, Retrofit Originality Incorporated (ROI) and RBF Consulting were named the project mechanical engineer and project civil engineer, respectively. Design began in December 2002. With a chilled-water district energy system, no changes were necessary to the existing system to make it compatible with a TES tank. Simply speaking, the tank stores chilled water generated by the existing chillers at night, and then uses the existing chilled-water loop to distribute this chilled water during the day. ROI’s Scot Duncan analyzed the existing system for sizing purposes only briefly, as optimizations were not necessary to make the existing system mesh with the new tank.

Another primary concern during the project planning phase was tank location. Given the university’s urban setting, there was little available above-grade space, and none allocated for a TES system. However, Welsh offered a creative solution that allowed the facilities management team to greatly expand their siting options: place the tank completely below grade.

Several sites had been analyzed during the predesign process. These were narrowed down to the Cromwell Field track facility and the Brian Kennedy and Howard Jones Fields football practice facility – the only available sites located near a cooling plant. Being near a cooling plant reduced the amount of piping to the tank and provided a location for the additional pumps and valves necessary for TES tank operation. In the end, after much debate, the Cromwell Field track facility was selected because it was the closest to the chiller plant. Given the anticipated fall and winter construction

window, construction there would also have less of an impact on the track team than it would on the football team, minimizing the need to relocate practices and competitions for USC’s sports teams.

Throughout project design and construction, the facilities management team kept all project stakeholders well-informed about its progress, which eased any potential challenges to approval and construction. During construction, facilities management also directly addressed the needs of the track team, which stood to benefit from the project by receiving new field turf.

A 30,000-ton-hr TES tank was selected based on campus cooling capacity and the amount of space available within the track facility. The 3 million-gal tank was the largest one that could be constructed within the selected site and could be recharged nightly with the existing chiller system. An AWWA D110 Type I prestressed concrete tank was chosen because it provided a maintenance-free, watertight tank. This cast-in-place concrete tank has performed well in seismic events, a key concern in the Los Angeles region.

The tank was designed with a 123-ft

Courtesy DYK Incorporated. Photo Warren Aerial Photography.

In May 2004, construction began on the University of Southern California’s 30,000-ton-hr TES tank (above). On completion of the project, the tank, buried beneath the Cromwell Field track facility, was no longer visible (below).