Designing for 'Ultra-Low' Efficiency and PUE

The ongoing industry debate about energy efficiency reporting based on the Power Usage Efficiency (PUE) metric is about to get another jolt. Veteran data center specialist KC Mares reports that he has worked on three projects this year that used unconventional design decisions to achieve "ultra-low PUEs" of between 1.046 and 1.08. Those PUE numbers are even lower than those publicly reported by Google, which has announced an average PUE of 1.20 across its facilities, with one facility performing at a 1.11 PUE in the first quarter of 2009.

Such claims are often met with skepticism. But Mares is well known in the industry from his work on the data center teams at Exodus and Sun, along withn his consulting for clients including Google, Yahoo, Equinix and Lawrence Berkeley Labs. Mares doesn't reveal the clients or get into details about the projects, but writes that these extraordinary PUE ratings are based on annual hourly site data, and the facilities in question are in the 10 megawatt range with power density of 400 to 500 watts per square foot and Tier III/N+1 redundancy.

"Most importantly, all have construction budgets equal to or LESS than standard data center construction," Mares writes. He says each of the sites have some renewable energy generation, it's not used to reduce the PUE, even though this tactic that could conceivably lead to a sub-1.0 PUE. "I don’t believe that is in the spirit of the metric," he writes.

"The main point of this blog post is to say that low PUEs, like that of 1.05, can be achieved for the same cost or LESS than a standard design, and done TODAY, saving millions of dollars per year in energy, millions of tons of CO2, (and) millions of dollars of capital cost up front," Mares writes. "We just need to really dive deep as to what we need, not what we want or think we need, and we’ll be better at achieving great things."