In 1996, Stanford University (Palo Alto, CA) was facing a cooling capacity shortfall with the chilled-water system it was using to cool about 70 academic and research buildings, as well as Stanford University Hospital. After careful cost analyses, Stanford decided to supplement its existing chilled-water system with an upgraded and expanded thermal storage system to handle the cooling needs of nearly 6 million sq ft of building space.

In operation since August 1999, the new thermal storage system currently uses three low-temperature, 2,250-hp screw-compressor chillers utilizing R-717 ammonia refrigerant, each dedicated to building ice on banks of externally galvanized steel coils in an existing 4-million-gal underground storage tank, previously dedicated to storing only chilled water. The result is a solution that builds on the strengths of the existing cooling system while effectively tripling the storage capacity within the existing tank structure. As a result, the new ice-on-coil technology enables Stanford to produce up to 93,000-ton hours of thermal storage nightly and generate chilled water during the peak daytime cooling period.