In terms of the fairness of the rating, I see potential drawbacks. Among them, the rating is designed to be one size fits all; you won't find different ratings for different categories of data centers. Consider two virtually identical data centers: same size, same location, same amount and type of IT equipment, but one is Tier I and the other is Tier III or IV. A higher-tier data center requires a higher level of redundancy to ensure uptime, which necessitates more backup equipment.
That, in turn, means a higher PUE compared to the Tier I facility, out of necessity, not because of inefficient practices. Yet the Energy Star rating puts the Tier I data center at a disadvantage because it applies the same predicted PUE to both facilities. It's akin to denying a workstation an Energy Star rating because it's not as energy-efficient as a notebook, even if it's more energy efficient than most other workstations.
The EPA says it did consider tier level when developing its model and found that "tier level did not show strong, statistically significant correlations with energy consumption."
Additionally, respondents within the industry requested that tier level not be factored in for various reasons. Among them, some data centers have multiple tiers, and "normalizing for tier level provides a disincentive for efficient design."
Haas, on the other hand, said he would expect some kind of segmentation down the road to recognize that data centers fall into different categories. The EPA does have that sort of segmentation for measuring the general energy efficiency of buildings based on their size and function, such as hotels, offices, and the like. "We'd expect that a similar approach would be taken for data centers," he said.
The rating also doesn't take into account other variables, such as climate. A data center located in a cooler part of the world arguably has a built-in advantage over one situated in a hotter climate, in that less mechanically generated cooling is necessary.
However, as with tier level, the EPA decided not to include climate as a variable. Among the reasons, "analysis does not show a statistically significant relationship between climate and energy consumption."
The Energy Star rating system for data centers -- like Energy Star for servers -- is a good first step, though it's certainly a work in progress. The EPA acknowledged this fact. Just as Energy Star ratings are updated periodically for computers and appliances to reflect inconsistencies as well as technological advancements, so too will this rating evolve.
In the meantime, it will set an efficiency bar for data center operators, encourage more organizations to measure power consumption, and (hopefully) improve the efficiency of their operations.
This story, "Energy Star for data centers has bright sides, dark sides," was originally published at InfoWorld.com. Follow the latest developments in green IT and read more of Ted Samson's Sustainable IT blog at InfoWorld.com.