PUE: Time to Start Grading on the Curve?

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Hundreds of data center professionals gathered n Las Vegas this week for the Spring AFCOM Data Center World conference. While there were several popular panels, the biggest crowd was for the networking luncheon at The Mirage Resort.

With a growing number of data centers reporting ultra-low Power Usage Effectiveness (PUE) ratings of between 1.02 and 1.3, it's clear that many data center have learned how to optimize for the best PUE possible. That's a step in the right direction, but does it reflect the everyday reality of building and operating a data center?

Scott Noteboom of Yahoo, whose Yahoo Computing Coop design has earned one of those industry-leading PUE ratings, says the facility's PUE of 1.08 has drawn global attention to the project in Lockport, N.Y. Noteboom is proud of his data center's efficiency. But that rating reflects a snapshot of the facility's operations at a point in time, he noted.

"Most of us in the data center have defined PUE while operating at the sweetest spot possible," Noteboom said Tuesday at the AFCOM Data Center World conference in Las Vegas. "We usually don't operate at that optimal PUE. On day one of the data center, before you have a lot of equipment installed, it's absolutely feasible that your PUE could be 100-plus."

The PUE metric championed by The Green Grid compares a facility’s total power usage to the amount of power used by the IT equipment, revealing how much is lost in distribution and conversion. PUE measurements tend to improve as a data center nears full utilization, which is one reason why large users such as Google, Yahoo and Microsoft report industry-leading ratings in the 1.1 to 1.2 rang

So how do you make the best use of PUE in building and operating a data center? Noteboom says he favors grading on the curve - the sloping curve as PUE readings gradually improve as the data center moves toward full utilization (and optimum PUE).

"We're seeing big wins in defining PUE at all levels of capacity," said Noteboom. "In order to truly model your electricity costs, you have to know your PUE at100 kilowatts and at 20 megawatts. We've been spending a lot of time focusing on how to build in increments."

Yahoo fills its data center capacity in pods of about 200 kilowatts each, Noteboom said. The mechanical and electrical equipment to support each pod is deployed when the pod comes online, allowing Yahoo to gradually increase its power requirements and match the IT load and facility power.

Noteboom was among the prominent speakers Tuesday at the spring Data Center World conference sponsored by AFCOM, the largest industry group for data center professionals. Former U.S. Ambassador John Bolton provided the keynote address. The AFCOM event continues Wednesday and Thursday at the Mirage resort in Las Vegas.