Is DC Power Right for the Enterprise?

Switching from AC to DC power has taken on new life recently considering the not insignificant efficiency gains that DC power could produce, theoretically at least.

By Arthur Cole | Posted Mar 11, 2010
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To some, the pursuit of the green data center is the IT equivalent of Don Quixote tilting at windmills. To others, it represents a sincere effort to reduce consumption at one of the highest class of energy consumers in existence.

Regardless of the perception, however, the fact is that the list of green ideas continues unabated, with everything from lawned rooftops to containerized power and cooling now on the table.

One of the ideas stirring up a fair bit of controversy is switching from AC to DC power. This isn't exactly a new suggestion, having been kicked around architectural circles for several decades. But it has taken on new life recently considering the not insignificant efficiency gains that DC power could produce, theoretically at least.

One proponent is Robert Farris, consulting vice president for environmental sustainability solutions at Hitachi. He argues that since most data center devices convert AC power from the wall into DC power anyway, it makes more sense to make the conversion at a single point and then pipe DC power straight to the racks. Such a scheme would cut the power loss from the combined individual conversions 20 to 30 percent and reduce heat generation up to 40 percent.

The chief downside to DC power, however, is that it is not as easily transmitted over even moderate distances as AC, according to Data Center Journal's Jeffrey Clark. So right off the bat, you're looking at replacing existing wiring with thicker cabling. There's also the fact that most legacy equipment is designed to accept AC power, so unless you're building a brand new center, you'll have quite a hefty capital budget to deal with.

There's also the uncomfortable fact that DC maintains a higher voltage level than AC, says searchdatacenter.com's Mark Fontecchio. That opens the possibility of dangerous power buildup and arcing within the wiring infrastructure that could damage sensitive equipment. Besides, a wide variety of efficiency measures for AC architectures are available at lower cost and could produce results similar to a switch to DC power.

At the moment, most enterprise power specialists are focused on squeezing as much efficiency out of AC is possible. Emerson Network Power, for one, offers DC-based products and services for those who want them, but most of its efforts go toward AC-related systems, such as the new SmartAisle cooling management system. Part of this is due to the fact that the vast majority of its market is wired for AC already, and it would take quite a concerted effort to change that.

Energy efficiency needs to satisfy two criteria to be successfully deployed in the modern data center. First, it needs to actually deliver on its promises -- reducing carbon emissions and lowering operating costs. Second, it needs a relatively simple implementation plan, one that not only won't bust the budget but won't disrupt legacy systems and operations.

DC power may satisfy the first requirement, but not the second.

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