Feb 17 2012

Innovating to Keep Data Centers Cool

Containment strategies maximize efficiency and reduce costs.

Carol Steele Sherman remembers a time, less than a decade ago, when Michigan had more than 40 data centers serving state agencies. She was part of the team that won an award from the National Association of State CIOs in 2007 for consolidating those data centers down to three.

Sherman, director of data center operations in Michigan's Department of Technology, Management and Budget, is still working to improve the state's data centers. During the past several years, she has focused on retrofitting the 30-year-old data centers that house the state's data to reduce heat and save energy.

The first step, taken about a decade ago, was separating hot and cold aisles, which Sherman says significantly improved heat dissipation. To address specific hot spots, her team used high-efficiency cooling techniques, such as implementing cooling equipment from Liebert (now Emerson Network Power). Still convinced that she could wring more efficiency out of data center equipment, she added chimneys on the data center air conditioners.

"Because we were dealing with older buildings — the primary production hosting center has only a 12-inch raised floor, and the most we had anywhere was 18 inches — we had to be creative," she says.

Around 2007, Sherman felt the time was right to try cold-aisle enclosures. Although the first foray into them wasn't successful — the technology wasn't mature enough yet, she says — Sherman knew she was onto something. Last year, she revisited the idea of cold-aisle containment in one of the state's data centers, installing cold-aisle enclosures with sliding doors that keep cool air contained. Sherman says it has worked so well that she plans to expand its use to a second data center.

Many organizations are moving to hot- and cold-aisle containment — available from manufacturers such as APC, HP, Tripp Lite and Black Box — to improve cooling efficiency and reduce costs.

"It's pretty much a given for new build-outs because higher-density equipment is so common today," says Jason Schafer, a research manager at Tier1 Research of Bethesda, Md. "Even five years ago, one to two kilowatts per rack was average, but now it can be 10kW per rack or more. That makes hot- and cold-aisle containment pretty important."

It can be difficult to retrofit existing data centers with hot- or cold-aisle containment, although it's not impossible. In many cases, it's worth the effort, Schafer says.

In Mississippi, Dr. Craig Orgeron, executive director of the state's Department of Information Technology Services, and his team are poised to add hot- and cold-aisle containment to the state's new data center, constructed barely a year ago. The new data center, with two levels and 12,000 square feet of raised floor space, services most of the state's mission-critical systems.

Both floors of the data center separate hot aisles from cold aisles. The first floor uses standard air conditioning units with forced air through the floor and is a candidate for cold-aisle containment.

The second floor, which houses high-density machines, uses APC's InRow cooling technology, but Orgeron believes it's only a matter of time before the floor gets some type of hot-aisle containment system.

"We built the data center with that possibility in mind. When the density gets to a point where it makes sense, we'll be ready. All of the racks are spaced out appropriately," he says. "All we would have to do is add top caps and end doors."

For more on power and cooling challenges, see how the City of Monroe, N.C., works to manage their ever-changing data center power and cooling needs.

Hot- Versus Cold-Aisle Containment

Without some type of containment system, heat will inevitably leak into the environment, reducing the efficiency of data center cooling efforts. The idea of containment — whether hot or cold — is to prevent the recirculation of air that has not been cooled, explains Jason Schafer, research manager at Tier1 Research.

With hot-aisle containment, racks are arranged in rows with the backs of the servers facing each other. Exhaust from the servers is emitted into the hot aisle and routed back to the computer room air conditioner (CRAC) unit. This way, hot air emitted from the servers is captured and prevented from entering the rest of the data center.

In a cold-aisle containment configuration, racks are arranged front to front, and the area between the rows is contained. That way, supply and return air are fully separated. Cold air reaches the cold aisles through a raised floor, and the hot air exhausted from the servers is routed from the racks back into the CRAC unit.

Each approach has its pros and cons, but combining them provides the best of both worlds, Schafer says.


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