Free cooling was not common in data centers in the past for a variety of reasons including the philosophy that data center cooling should be designed for maximum reliability and not for energy efficiency. Recently times have changed. Energy and sustainability are more important to many data center owners now and sophisticated owners and designers know that free cooling can provide a good return on investment while still maintaining adequate reliability. Many data centers are being designed or retrofitted with airside economizers, waterside economizers, and even "wet bulb" economizers (direct evaporative coolers). This paper briefly compares airside and waterside economizers, then briefly compares the two types of waterside economizers (CRAC and chiller plant) and then focuses on design and control considerations for chiller plant waterside economizers serving data centers.

Units: I-P