The NetApp RTP data center is a two-story building that employs a top-down cooling system that uses fresh air from outside of the building to cool the server rooms, a process also known as air-side economization or simply "free cooling." Fresh air is used to cool the data center whenever the outside air is cooler than the return air, which is 97 percent of the year under the operating parameters used by NetApp, which uses only outside air for 67 percent of the year, and a combination of free cooling and chillers for 30 percent of the year. The chilled water plant is the sole provider of cooling only 3 percent of the year.
"A big key is the ability to turn off the chillers," said Miller. "That's where we get a huge savings on electricity."
The air flow management begins on the roof of the building, where air inlets (pictured below) bring outside air into the building.