The model, as you would expect, is intended to reward companies that embrace more energy-efficient practices. In a presentation to The Green Grid earlier this year [PDF], the EPA provided an example of how using an economizer, for example, would boost a data center's rating. In the scenario, two identical data centers -- same UPS energy consumption, same size, same climate -- would have the same predicted PUE of 1.87.
The differentiator: One data center would employ an economizer for cooling, which would result in 20,000 fewer MBtu consumed per year. That, in turn, would reduce the facility's actual PUE from 1.73 to 1.64. As a result, its Energy Star rating would be 70 instead of 60.
Two questions in particular spring to mind when considering this data center rating: Is it effective, and is it fair?
The system is certainly effective insofar as it should motivate data center operators to measure the energy efficiency of their facilities, the first critical step in reducing waste. Additionally, companies that boast of exceptionally low PUEs and high levels of efficiency can now prove it in a standardized, verifiable way.
One of the drawbacks, however, is that it's based heavily on PUE, which has garnered some criticism for not being an entirely effective tool for assessing a data center's overall efficiency. One of the most common cases against PUE: A data center has 100 servers working at 80 percent utilization, 24/7. Its actual PUE is 1.25. An absolutely identical data center has the same 100 servers -- but they're idling 24/7, while drawing the same amount of energy. The second facility's actual PUE is also 1.25, despite the gross inefficiency. In other words, a data center bearing the Energy Star label may still be inefficient.
[ The Uptime Institute's Kenneth Brill cautioned not to get too caught up in PUE.]
Jon Haas, technical committee vice chairman for The Green Grid, said that the group supports the EPA's efforts and its decision to embrace PUE as central to the rating. However, Haas, who is also director in the Eco-Technologies Programs Office at Intel, indicated that the rating is but a first step in developing a meaningful energy-efficiency standard for data centers. "We're starting to talk about [IT hardware] productivity and efficiency. We have efforts in that space to realize those metrics. That will take some time; it requires a lot more heavy lifting," he said.