Power Supply Options for Data Centers

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For many federal facilities, the fastest growing end-use of electric energy is found in concentrations of computing capacity commonly known as data centers. For these users, the critical importance of information processing to their agency mission will present a serious challenge to meeting the aggressive new energy efficiency goals in Executive Order 13423. Federal energy managers can find a variety of methods for reducing energy intensity, in both design and operations, for these high-technology facilities . This report summarizes a recent demonstration of one such technique — configuring power supply systems for data centers so that they use DC (direct current) power throughout, eliminating the conventional practice of multiple conversions from utility-supplied AC (alternating current) to DC and back again at every stage of the power supply system. This eliminates both the power loss and heat generated by each such conversion (which drives air conditioning energy use).

The demonstration suggests that direct powering, coupled with selection of high-efficiency power-supply components, can result in as much as 30% improvement in power conversion and distribution to IT equipment as well as overall facility level efficiency, when compared to a typical AC-powered data center. Data do not exist for more than the broadest ballpark estimate of energy use in federal centers, which suggests an order-of-magnitude figure of as much as 6 TWh/year. While data processing equipment decisions are made on the basis of many criteria other than energy efficiency, and no systematic effort was made in this demonstration to estimate the cost-effectiveness of retrofit of power supplies, this demonstration does suggest that federal data centers could potentially be using as much as 1.8 TWh/year less energy.

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