The use of the Internet is exploding, but fortunately, the consumption of electricity isn't increasing at the same pace. That's true in part because, pound for pound, computers in the cloud run more efficiently than those in a traditional data center.

The Environmental Protection Agency predicted in 2007 that the amount of electricity consumed by data centers would double between 2005 and 2010, based on the rate of new construction it was witnessing. Google, Amazon, Facebook, and dozens of other participants in the digital revolution, including co-location service providers and managed service hosts, have built new data centers, as projected. In spite of that, electricity growth for data center use over the five-year period in the U.S. was 36%, not 100%.

That's the figure that Jonathan Koomey, consulting professor in civil and environmental engineering at Stanford University, came up with as he re-examined the EPA's projections. He attributed the slowdown primarily to the recession and secondarily to more efficient technologies, such as virtualization, slowing demand for new servers.

Still, John Markoff, writer for the New York Times, was impressed with how far off consumption was from the projected 100% increase. "The slowdown in the rate of growth of electricity use is particularly significant because it comes in the midst of the biggest build-out of new data center capacity in the history of the industry," Markoff wrote in his column July 31.

If a massive build out has occurred, why didn't electricity consumption grow accordingly?

I suspect recession, virtualization and more efficient chips do not account in full for this fall-off from the EPA's original projection. Neither the EPA's report or Koomey's second look at electricity consumption get the complete measure of what's happened in data center design.

A significant share of new data center construction has been by the new companies succeeding on the Web--Zynga, Facebook, Apple, Google, Amazon.com. But they account for a relatively small percentage of the total number of data centers, with enterprise centers far outnumbering this new construction. Google is probably constructing data centers on an annual, if not continual, basis, or leasing space in wholesale data centers. No one knows for sure, but it is believed to have at least 36 at this point. Google, a pioneer of modern data center design, told Koomey that its data center power use, while large, constituted less than 1% of the worldwide power consumed by data centers. Its pattern of efficient data center construction, which other vendors are emulating, could have had a depressing effect on the projected energy consumption growth rate.

Google has played its cards close to the vest on what constitutes advanced data center design. It builds its own servers, then places them in racks with baffles of its own design that manage the air flow through the racks. It uses a water evaporation system for cooling ambient air as a substitute, when possible, for running air conditioners, a process that's now known as economization in cooling. Amazon, Microsoft, and others have followed Google's lead and come up with their own variations.

Facebook also designs its own servers, racks, and data centers. Unlike Google, it published the specifications April 7 at its OpenCompute.org site. Facebook itself showed that efficient data center design can be specific to a facility's location. In Prineville, Ore., Facebook maximized economization by building where it's cool and dry much of the year. The low humidity of the high desert creates a good climate for evaporation, and evaporation is used to reduce the peak summer outside temperature of 85 as much as 35 degrees as they bring outside ambient air into the data center, said Brent Kerby, AMD's guru of server power management, who visited Prineville two months ago.

Facebook then uses an air filtration and distribution system to push the air through big overhead fans down into the "cool" aisle of the data center, where it flows across server motherboards that have been removed from any kind of casing. Cool air is propelled by the servers' own fans across the exposed components, picking up heat and exiting into the hot aisle. The hot aisle collects warmed air coming off two adjacent rows of servers. It is then pumped out of the building.

Kerby said walking down the hot aisle in some data centers is an uncomfortable experience. At Prineville, "What most impressed me was the whole data center climate control system. This was the first data center where I have walked down the hot aisle and it wasn't that bad. It was truly amazing to me how they set up their air flow control," he said in an interview. He added the hot aisle was warm, 90 degrees, but other hot aisles he's encountered have been warmer and more humid.