Direct-current model slashes power costs

Datacentres can save significant amounts of power - and cash - by doing away with the changeover from alternating to direct current

Of all the waste in the typical datacentre, none is as often overlooked as the series of steps that convert power back and forth from AC (alternating current) to DC (direct current). My Ton, senior project manager at environmental consulting firm Ecos Consulting, aims to change that. Ton says companies can cut power usage by more than 20% by retooling their datacentres to run on DC.

Under the typical topology, power arrives at the server room as AC, where it is converted to DC so it can be stored in uninterruptible power supplies. The power is then converted back to AC so it can be transported to other parts of the facility and then back again to DC by the power supply inside each server, router, load balancer or other piece of networking equipment.

Each conversion step results in power dissipation in the form of heat. “What you have is several layers of conversion and every time you convert you lose,” Ton says.

Earlier this year, Ecos Consulting joined approximately 50 companies, including Intel and Sun Microsystems, to figure out what it would take for datacentres to convert power to DC only once. Telecommunications companies have been employing DC power in their switching centres for decades. Ton and the other participants adjusted the telcos’ model, converting the AC power to the 380-volt DC preferred by most servers. They then fed the DC current to specially modified servers that could accept it directly, eliminating the intermediate conversion steps. Remarkably few specially designed components were needed to build the alternate topology. They used commercially available rectifier units, a common brand of busway power distribution hardware, and standard three-prong power cords.

The finding: building datacentres that run on DC was relatively easy, eliminated a lot of costly equipment, and could boost power efficiency by about 20%. All that stands in the way of widespread usage, says Ton, are vendor standards for plugs, cords, rectifier units and other DC gear.

Data393 runs a modern datacentre that uses DC for most of its hosting operations. “By the time the DC gets to my server room, I’ve reduced the heat load by 30%,” says Steve Merkel, the company’s senior systems engineer. Merkel estimates the DC power system shaves as much as 20% off the electric bill for the hosting side of his business. But so far, Merkel’s enthusiasm has not rubbed off on Data393’s co-location customers, who by and large still opt for AC.

“People are looking at that initial up-front cost and shying away,” he says.

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