Analysis of Alternative Data Center Cooling Approaches

The average equipment rack in most of today’s high-performance data centers is limited to 1–3 kW with a typical overall heat load density of less than 100 W/ft². Near-future racks, however, will dissipate up to 15 kW; in 2–4 years, computer and communications rack heat loads are projected to balloon to 30 kW with heat load densities exceeding 500W/ft². Handling these heat loads is becoming increasingly difficult and expensive using traditional rack and data center cooling approaches. Based on an analysis of a realistic data center expansion plan, the current paper compares capital and operating costs associated with three alternative cooling approaches: (1) a business-as-usual approach, (2) employment of cooling augmentation systems based on chilled water and refrigerant-based heat exchangers, and (3) deployment of water- and refrigerant-based device-level cooling for some of the heat load. A major conclusion of the work is that challenging current industry norms can result in significant energy savings while allowing the benefits associated with increased functional density.