Typical power chain conversions waste energy. Power flows into most data centers at a high voltage, is converted from AC to DC, and then back to AC in Uninterruptible Power Supplies (UPSs). Voltage is then dropped in Power Distribution Units (PDUs) and converted from AC back to DC in individual server power supplies. This process is extremely inefficient as each transition results in energy losses and heat, which in turn must be removed by the cooling system.

UPSs, front-end AC-DC power supplies, and DC-DC converters are three important conversion processes for powering of servers and other IT loads in a data center. Improving the efficiency of these processes can significantly improve the overall energy efficiency of a data center. Storage is a parallel area of importance.


  • Re-Examine Power Redundancy Requirement
  • Increase the Load factor on UPS Units by Running Some Offline
  • Load Equipment at the Range Where the Best Power to Performance Ratio can be Resulted
  • Optimize Standby Generator Block Heater Energy Use
  • Install Premium-Efficiency Motors
  • Use Modular UPS
  • Increase High Voltage Distribution and Reduce Conversions
  • Switch to Direct Current (DC)
  • Power Move to Renewable Sources

The purchase of efficient power supplies, such as ENERGY STAR or Climate Savers, is also recommended. It is worth noting that although power supply efficiency has been improving, there is still a large variation in performance. 


  • Data Center Master List of Efficiency Actions provides more information on the high-level best practices outlined above as well as a more detailed list of best practices related to IT power distribution chain.
  • Datacenter Electrical Power Chain Assessment Tool helps to assess the potential savings from efficiency action in the electrical power chain of a data center (transformers, generators, UPSs, and PDUs).
  • Calculating Energy Savings Using High Efficiency Power Conversion in Server Applications Tool is an Excel-based calculator that provides a first-order estimate of the magnitude of the energy savings based on improving the efficiency of any one or more of the elements (UPS, AC-DC and DC-DC power supply) involved in powering a rack of servers.
  • Data Center Metering and Resource Guide provides guidance on measuring power usage effectiveness (PUE). PUE is the ratio of total energy use to that of energy used by information technology (IT) equipment, which provides insight into how much energy is used for power delivery components, cooling equipments, and lighting compared to IT.
  • DC Power for Data Centers of the Future outlines the benefits of using a Direct Current (DC) Power distribution scheme throughout a data center instead of the conventional Alternating Current (AC) power. Although this website has not been maintained, it hosts valuable information on DC Power.
  • Federal Energy Management Program (FEMP) page for purchasing energy efficient UPSs provides federal agencies with guidance on calculating cost-effectiveness, claiming an exception to purchasing requirements, incorporating Federal Acquisition Regulation language in contracts, finding federal supply sources, and tips to user products more efficiently.