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COMPUTING SCIENCE

The Computer and the Dynamo

Brian Hayes

How Much and How Many

Another group of energy analysts has undertaken a direct rebuttal of the Huber-Mills thesis. At the Lawrence Berkeley National Laboratory, Jonathan G. Koomey heads the Energy Analysis Department of the Environmental Energy Technologies Division, which has carried out numerous studies of energy consumption, mostly funded by the Department of Energy and the Environmental Protection Agency. When the Forbes article appeared, Koomey immediately disputed its conclusions, citing data from his own group's survey of energy use by computers and other office equipment.

Koomey and his colleagues question nearly all the assumptions that underlie the Huber-Mills energy estimates, starting with the power demands of individual machines. A desktop PC is not a 1,000-watt device, Koomey says, even if the nameplate attached to the chassis gives a rated power in this range. For a 500-megahertz Pentium III computer and a 17-inch monitor, Koomey's measurements indicate that power demand is no greater than 150 or 200 watts, even including a share of the electricity consumed by a workgroup laser printer. For the somewhat larger computers used as servers, Huber and Mills specify 1,500 watts, and Koomey reduces it to 300. In the case of mainframe computers the disparity is even greater. For these machines Huber and Mills adopt a figure of 250 kilowatts (half for the computer itself and half for air conditioning). Koomey finds that only exotic supercomputers with hundreds of processors approach this level of power use, and that a more realistic estimate for a typical mainframe is 10 or 20 kilowatts.

There are also disagreements about counting. Relying on a compilation of computer sales statistics, Mills asserts that the inventory of computers in use is growing by 40 million a year. Koomey points out that some fraction of the new computers are not additions to the stock but replacements for retired equipment. (The EIA says that computers in offices are nearing "saturation," with four computers for every five employees.)

In August 2000 the LBNL group released a new report on power consumption by computers and network equipment, with further supporting data published in February 2001. The survey includes energy used by all kinds of office machinery, including not only computers and their peripherals but also unrelated devices such as copiers and fax machines. The conclusion: The entire spectrum of equipment dissipates 74 terawatt-hours per year, which is about 2 percent of U.S. electricity consumption. Adding in an allowance for a few other items that Huber and Mills count (such as the energy needed to manufacture computers, and a share of the energy consumed by telephone switchgear) brings the total to 3.2 percent—still only a fourth of the 13 percent level claimed by Huber and Mills.

The debate between Huber and Mills and their critics has been conducted via letters to the editor, press releases and public e-mails. The tone has not always been collegial. In February 2000, when Mills testified before the House Subcommittee on National Economic Growth, Natural Resources, and Regulatory Affairs, he seized the opportunity to defend his ideas against the attacks by Koomey and others. Koomey responded with a memo offering further rebuttal. He wrote: "In the past year and a half, I have been witness to an extraordinary event: an analysis based on demonstrably incorrect data and flawed logic has achieved the status of conventional wisdom, in spite of my and my colleagues' best efforts to refute its assertions. The results continue to be cited by an unsuspecting press, and even by people who ought to know better."

A further year and a half later, the "conventional wisdom" is still very much in circulation. A few weeks ago, Roger N. Anderson of the Lamont-Doherty Earth Observatory published an op-ed essay in the New York Times alluding to the Huber-Mills conclusions, with no hint that they might be controversial.





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