Data centers occupy less than 2% of the federally owned portfolio under the jurisdiction, custody or control of the U.S. General Services Administration (GSA), but represent nearly 5% of the agency's overall energy budget. Assuming that energy use in GSA's data centers tracks with industry averages, GSA can anticipate that data center energy use will grow at an annual rate of 15%, a doubling of energy use every five years.1 In fact, energy is the single largest operating expense for most data centers. Improving the energy performance of data center systems supports progress toward meeting federally mandated greenhouse gas emission-‐reduction goals, while reducing operating and energy costs and allowing for greater flexibility in future expansion by eliminating the need to provide additional power and cooling. Studies sponsored by the U.S. Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA) have shown that energy use can be reduced by 25% through implementation of best practices and commercially available technologies. The present study evaluated the effectiveness of a strategy to cost-‐ effectively improve the efficiency of data center cooling, which is the single largest non-‐IT load. The technology that was evaluated consists of a network of wireless sensors—including branch circuit power monitors, temperature sensors, humidity sensors, and pressure sensors, along with an integrated software product to help analyze the collected data. The technology itself does not save energy; however, its information collection and analysis features enable users to understand operating conditions and identify problem areas. In addition, data obtained by this technology can be input into assessment tools that can identify additional best practice measures. Energy savings result from the implementation of the best practices. The study was conducted to validate the premise that providing data center operators with detailed, real-‐ time measurement of environmental parameters and power consumption enables them to establish baseline performance, discover areas of sub-‐optimal performance, and identify concrete opportunities for improvement. Real-‐time measured performance data was collected in a demonstration facility at the U.S. Department of Agriculture's (USDA) National Information Technology Center (NITC) Data Center in St. Louis, Missouri, to validate the effectiveness of these improvements, enable further fine-‐tuning of systems, verify savings, and report results. Wireless sensor technology was selected because, in contrast to wired sensor technology, it can deliver the data in a cost-‐effective, facility-‐friendly way.2 After wireless sensor technology was deployed at the demonstration facility, implementation of the identified efficiency measures was used to reduce the data center's cooling load by 48%, reducing total data center power usage by 17%. This represented an annual savings of 657 megawatt-‐hours (MWh). There was also a corresponding reduction in the data center's Power Usage Effectiveness (PUE), from 1.83 to 1.51. The data center's carbon footprint was reduced by 542 metric tons annually.