The savings that Scottrade achieved are actually on the low side, says Graves. "Scottrade was already doing a lot of things right," he adds, noting that Glumac has seen some data centers that achieve a 25% decrease in cooling costs when tuned properly.

The CFD model identified three key areas for improving efficiency. First, it found that a "thermocline," or plane of warmer air, was floating in the upper half of the data center space. That hot layer started at a height of about five and a half to six feet and extended all the way to the 10-foot ceiling. Thus, the equipment in Scottrade's top racks was in the hot-air cloud.

The second issue was the configuration of the racks themselves. Not all racks were fully populated, but equipment was always concentrated at the top of the racks, where it was subject to those higher temperatures. In fact, says Patterson, the hottest-running servers tended to be mounted at the top, where cooling efficiency was lowest. To address that, Scottrade had lowered the CRAC system temperature settings, overchilling the rest of the room.

"Scottrade was running the overall data center temperatures colder than necessary to keep the temperatures at the top of the racks within acceptable ranges," Graves explains.

Finally, the balance between the heat load produced by the server racks and the quantity of air supplied to the cold aisle was out of whack. Engineers redistributed the perforated tiles on the aisle floor to match the output required. "A thermal balance was noticed immediately," says Graves.