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Data center hoster uses flywheels to save space

To save data center space, Terremark Worldwide, a large data center hoster, uses flywheel- rather than battery-based uninterruptible power supply for a new facility's backup power.

Data center hosting giant Terremark Worldwide Inc. is installing flywheel-based uninterruptible power supply (UPS) units at a new facility in Santa Clara, which is due to go live April 1. Though battery-based UPSes are still the preferred choice of most data center managers, flywheels have are the choice of some. Formerly produced by smaller companies, they are now being sold by large players such as Liebert Corp. Ben Stewart, the senior vice president for facilities engineering at Terremark, spoke to about why the company uses flywheel UPSes. One surprising answer: to save data center space.

You chose flywheels for backup power at Terremark's new data center in Santa Clara. Why?
Ben Stewart: The biggest reason we go with flywheels is that [they take] up so much less room. You don't have to set aside so much space for the battery room. Plus flywheels can sit in pretty much any weather, they weigh less and, with battery strings, you have to swap them out every five years at $100,000 a string.

What do you mean by "any weather"?
B.S.: It's a temperature thing. With batteries, the optimal temperature is a static temperature. Just as with a car, if you're up north, and the temperatures have big swings, your battery craps out easier. It turns out that 77 degrees [Fahrenheit] is a good static temperature for batteries. With flywheels you don't have to worry about temperature.

Terremark has run flywheel UPS for some time now. Can you explain the evolution of Terremark's use of them?
B.S.: There are two kinds of flywheels on the market: rotary UPS and flywheel battery UPS. A rotary UPS is spinning to power the floor between the utility and the generator. Our very first data center used rotary UPS. We started using flywheel battery units in Culpepper, Va. In the Active Power flywheel battery units we have, instead of using traditional batteries to create DC [direct current] power for the inverters, you use flywheels to create it. So you can use the front end of almost any UPS on the market and replace the battery string with flywheels.

Mark Fontecchio can be reached at

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