By Mark Henricks

Any moderately bright kindergartner can tell you what “green” is without having to think about it for more than a second or two. When it comes to eco-efficient IT, matters become more complex.

The colossal dollars tied to regulating, marketing, budgeting and selling IT on the basis of how green it is or isn’t mean that taking a kid’s -- or anybody’s -- word for what green is simply won’t fly. What we need is a global standard by which we can instantly understand how green a supposedly eco-efficient IT product, service or initiative really is.

That need underlies a new effort by a powerful roster of regulatory and advocacy organizations to write down some guiding principles for measuring data center energy efficiency. The group includes representatives from governmental heavyweights including the U.S. Department of Energy, the U.S. Environmental Protection Agency, the European Union Code of Conduct, the Green Grid, Japan Green IT Promotion Council and Japanese Ministry of Economy, Trade and Industry.

The just-formed and somewhat loosely organized group doesn’t have much progress to report yet. However, it has marked one initial milestone by selecting Power Usage Effectiveness (PUE) as the metric by which eco-efficiency in IT will be judged. PUE has been backed by Beaverton, Ore.-based Green Grid as its preferred metric and is already widely referenced by organizations from Microsoft to IBM as a yardstick for distinguishing between IT that is merely asparagus-colored as opposed to genuine jungle green. To the extent PUE is already a standard, the consortium’s choice just cements existing practice. But it’s still worth a review of PUE to make sure you know a little about what it is, and isn’t.

PUE is a ratio, calculated by comparing the total energy consumed by a data center, notably including cooling requirements, to the so-called useful energy consumed by servers alone. A commonly reported industry average for PUE in a conventional data center is about 2.5. This means that a large majority of the energy used by the data center goes to power secondary equipment such as cooling systems, rather than servers.

While PUE is simple, straightforward and easy to calculate, its limitations suggest that it won’t be the only important way IT’s greenness is going to be measured. For instance, a PUE figure doesn’t directly reveal the total amount of energy a specific data center uses.

Another limitation is that it doesn’t tell you where the energy being consumed comes from. A high-PUE data center that got a lot of its energy from on-site solar or wind generators, for instance, might legitimately be considered greener than a lower-PUE center that relied on electricity from a grid reliant on conventional coal-fired plants. Other potentially interesting metrics could tell how much power individual applications consume, as well as a host of green disposal, sustainable manufacturing and related issues, some of which are likely more significant contributors to IT’s overall environmental impact than data center efficiency.

It’s critical for IT individuals and organizations concerned with eco-efficiency to understand and, if possible, guide the adoption of the yardsticks that will be used to measure their future. That process doesn’t begin or end with PUE. But with support from the likes of the EPA’s highly recognizable Energy Star designation, and with apologies to future generations of kindergarteners, from now on it looks like it’s going to be difficult if not impossible to spell “green” without “PUE” in it somewhere.

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