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Data Center Energy Use: Truth versus Myth

At the height of the electricity crisis of 2001, Californians were greeted over their morning coffee with headlines like:

Digital Economy's Demand for Steady Power Strains Utilities
Data Servers Crave Power: High-Tech Electricity Needs Amplify Crisis

and
Net Blamed as Crisis Roils California.

One of the biggest misconceptions about the crisis was that the energy use of computers and other internet-related hardware played a significant role.

But early in 2001, research by Jon Koomey of Berkeley Lab's Environmental Energy Technologies Division (EETD) showed that widely discussed estimates of the energy use of computer- and networking-related hardware were exaggerated. Koomey is leader of EETD's End-Use Energy Forecasting Group. His work proved that this equipment used about three percent of the electricity consumed in the U.S.-a striking contrast to the 13 percent figure widely cited in the media.

New information on data centers

Questions persisted about the use of energy by data centers, facilities also known as "web server farms," which have become more common as the internet has expanded as a commercial entity. Data centers can house thousands of computers that store and transmit the data and web pages available on the internet.

Two recent developments at Berkeley Lab focus new attention on data centers.The first is a study by Jennifer Mitchell-Jackson, Koomey, and others. This study concludes that the energy use of data centers is often overestimated. The second development is the announcement of a $500,000 grant to Berkeley Lab from the California Energy Commission to study the data centers in California, benchmark their energy use, and develop a research and development "roadmap" with the objective of reducing their energy use by 30 percent.

"Many reports of data center energy use are exaggerations," says Mitchell-Jackson. "They arise from a lack of measured data from operating data centers, inconsistent definitions of the power consumption in these facilities, and use of rated or design power instead of actual power when estimating total consumption. Rated power is typically several times greater than actual power use."

"These overestimates of data center power use can leave utilities with expensive generation, transmission, and distribution capacity sitting idle," says Koomey.

Schematic layout of an internet data center (Sun Microsystems).

Schematic layout of an internet data center (Sun Microsystems).

Total electricity use about one-tenth of one percent

Questions persisted about the use of energy by data centers, facilities also known as "web server farms," which have become more common as the internet has expanded as a commercial entity. Data centers can house thousands of computers that store and transmit the data and web pages available on the internet.

"The research found that in the U.S. there were about 9.5 million square feet of hosting-type data-center space in 2000. Our measurements suggest that these data centers have computer rooms that use an average of 50 watts per square foot or less," says Mitchell-Jackson.

She continues, "The total use of electricity by hosting-type data centers in 2000 was less than 500 megawatts of power or 0.12 percent of the total electricity use in the United States in 2000." Total electricity used by these facilities is therefore small in the aggregate although the clustering of data centers in certain regions may strain local electricity distribution and supplies.

Server-farm power density exaggerated

During the past few years, utilities in California, New York, and Washington state have received requests for tens to hundreds of megawatts of electric capacity for new data centers. The requests created concern that these new power demands would overwhelm generating capacity in these states.

The team studied one data center in the San Francisco Bay Area in detail, measuring energy consumption of servers, power distribution units (PDUs), uninterruptible power supplies (UPSs), air distribution, and other building loads. To express energy use accurately, Mitchell-Jackson developed a measurement called "total computer-room power density," a metric that is most representative of a data center's power needs because it includes power drawn by computers and all supporting equipment, including PDUs and UPSs; heating, ventilation, and air-conditioning systems; and lighting.

Measurements at the center in the Bay Area revealed that total computer-room power density at the facility was 33 watts per square foot. In the five facilities for which billing data were available, the figure was always below 40 watts per square foot.

"Our hope is that the data center industry and electric utilities will use this research to better estimate their energy needs, resulting in more efficient use of energy in these facilities, more reliable supplies to the data center operators, and more accurate planning for utilities," says Koomey.

The research was conducted by Jennifer Mitchell-Jackson, a graduate student in the Energy and Resources Group at the University of California at Berkeley, working with Jon Koomey and Bruce Nordman of Berkeley Lab's Environmental Energy Technologies Division. Their results are contained in two refereed journal articles, one recently accepted by Energy—The International Journal and one that appeared in a recent special issue of Resources, Conservation, and Recycling.

— Allan Chen

For more information, contact:

  • Jon Koomey
  • (510) 486-5974; fax (510) 486-4247

For more information, see:Information Technology and Resource Use

This work was funded in part by the U.S. Environmental Protection Agency, Office of Air and Radiation.

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