The problem is getting worse, too, since smaller processors mean more are squeezed into the same volume. “As recently as the year 2000, the average server consumed on the order of 100 to 150 watts,” says Vinson. “It’s now exceeding 400 to 500 watts. And it would not be unusual to have a rack of servers that pulls 15,000 or 20,000 watts” – enough to light more than 100 homes.
While U.S. computer manufacturers for years have been pushing mostly Chinese makers of computer fans to rethink their products’ motor designs and aerodynamics, the amount of air these traditional fans can push through has been increasing by no more than 5 percent per year. This lack of real progress has loomed as a potential roadblock in the development of server technology. “By 2003, we had an idea of what we wanted our future servers to look like – but when we started doing the calculations about the type of fan that would be needed to go there, it was three times what anybody in the industry would be able to deliver,” says Vinson.
Eventually Vinson and Ron Noblett, vice president of shared engineering services at the HP Industry Standard Server group, stumbled on the unorthodox solution. Noblett, a model airplane enthusiast, suggested that his colleague examine the electric-ducted fans used in radio-controlled jets.
Most propeller-driven model airplanes carry small gasoline engines (which produce that familiar high-pitched whine). But gas engines aren’t ideal for model jets. These $4,000 toys can buzz about at more than 200 kilometers per hour, requiring lightning reflexes; if a pilot loses control, the plane’s fuel tank can turn into a flying bomb. So in the mid-1980s, hobbyists started developing high-speed, battery-powered electric motors that could be placed in the fuselage or under the wings of a model plane.
“Over the last 20 years, this electric flying industry has kept pushing battery power, motor technology, and fan blade technology under the premise that even if they go too far and the motor dies in flight, the plane still has its control surfaces and just becomes a glider,” Vinson says. Adapting this new model-jet technology for cooling servers turned out to be a simple matter of changing the blade shape.
HP and rivals are also working on other ways to solve the problem of excessive heat. There’s water cooling, in which heat sinks are replaced by “water blocks” with channels for flowing water; phase-change cooling, which is similar to traditional refrigeration; and Peltier cooling, based on the Peltier effect, in which a current passing through two types of metal causes one to heat up and the other to cool. But a flow of air is still the simplest way to disperse heat.
“Because we’re able to take these high-power EDFs and re-engineer them, the guy with the data center, knowing he’s got this technology, doesn’t have to worry about doing an upgrade of his cooling systems two years from now, and a rip-and-replace five years from now,” says Vinson. He adds: “We don’t think we’re even close to running out of room to improve this technology.”
Home page image: The HP electric-ducted fan in its finished housing. (Courtesy of Hewlett-Packard.)
When designing an embedded system choosing which tools to use often comes down to building a custom solution or buying off-the-shelf tools.