In "ice-build mode," which usually starts about 7 p.m. each evening, the solution of Dowtherm SR-1 fluid is chilled to 18[degrees]F and pumped to the banks of coils inside the underground storage tank, where it freezes the water in the tank surrounding the coils. The solution flows at 28,000 gpm until full ice-build is reached. This mode could take as little as eight to 10 hours or as long as 14 hours, depending on the weather and cooling loads expected for the following day. The screw chillers are run from 7 p.m. to 11 a.m. to take advantage of the lower electrical rates and to minimize electrical use during the daytime peak period from noon to 6 p.m.

In "ice-burn" mode, which runs from noon to about 6 or 7 p.m., glycol pumps are started and the heat transfer fluid flow is switched from the screw chillers to glycol-to-chilled-water plate-and-frame heat exchangers. The solution of Dowtherm SR-1 fluid enters the plate and frames at 34[degrees] and then returns to the storage tank at 53[degrees] to start melting the ice on the coils.

On the other side of the plate-and-frame heat exchanger is the campus chilled water, which is cooled from 58[degrees] to 41[degrees]. When the load on the campus cooling system starts to level off in the early evening, the plate-and-frame heat-exchange system shuts down, and the system is then switched back to ice-build mode.