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An EPRI White Paper

DC Power Production, Delivery and Utilization

Numerous Silicon Valley giants including Intel, Cisco, and oth- ers are participating and contributing to the project, including Alindeska Electrical Contractors, Baldwin Technologies, CCG Facility Integration, Cingular Wireless, Dranetz-BMI, Dupont Fabros, EDG2, Inc., EYP Mission Critical, Hewlett-Packard, Li- ebert Corporation, Morrison Hershfield Corporation, NTT Fa- cilities, Nextek Power, Pentadyne, RTKL, SBC Global, SatCon Power Systems, Square D/Schneider Electric, Sun Microsys- tems, TDI Power, Universal Electric Corp., and Verizon Wire- less.

Potential savings and benefits of DC power delivery in data centers

The existing AC-based powering architecture in a data center, which requires multiple AC-DC-AC conversions, can have an overall system efficiency lower than 50%. How much energy and money could be saved by eliminating these multiple con- versions? Field performance data are yet to be documented. However, preliminary estimates of energy savings indicate that about 20% savings could be realized by changing from AC-based powering architecture to DC-based powering archi- tecture for a rack of servers. Table 2 shows one estimate from EPRI Solutions, which indicates that a typical data center of 1,000 racks could save $3.5 million annually by using a DC power delivery system.

Total input power

air conditioning

Total savings

Yearly energy

Yearly energy

value (NPV) of




savings (MWh)

savings ($)

savings ($)

Net present


Table 2a. Energy savings estimate for one rack of servers with high-efficiency power conversion

Reduction due to

AC power*


DC power








*The efficiencies for the AC system are based on typical, rather than best-in-class systems. If a best-in-class AC system is compared to a DC best-in-class system, the savings from use of DC power would be reduced. For instance, yearly energy savings might be about $873 rather than $3428. However, gains in reliability from DC power (not shown in this table) would not be achieved. Only energy-related savings are considered; other savings such as size and heat sink cost not considered. Calculations are based on typical power budget for a dual 2.4 GHz Xeon processor based 1U server rack 1U = TK Energy cost = 12¢/kWh; project life = 4 years; discount rate = 6%; Overall cooling system efficiency = 1,200 Watts/ton; number of 1U servers per rack = 40

Table 2b.Assumptions

Power conversion efficiency UPS AC/DC PS DC/DC VRM (12V – 1.75 V) DC/DC (48V-12V) Nextek power module 1U dual processor server power budget Dual processor power (@1.75V DC)

Mother board, PCI Card, DDR memory and other peripheral DC power consumption (@12V, 5V, and 3.3V DC)

AC power architecture 85% 72% 84% N/A N/A Typical (W) 60 60

DC power architecture N/A N/A 84% 95% 92% Maximum (W) 130 220

To calculate energy savings estimates for different design configurations or using different assumptions, visit an Excel-based calculator, available at the Lawrence Berke- ley National Laboratory website (http://hightech.lbl.gov/DC-server-arch-tool.html)

June 2006

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