The US Environmental Protection Agency is wrapping up work on an Energy Star program for data centres that it hopes to launch in June, EPA officials said this week.

The goals of the program are to give organisations more incentive to improve the energy efficiency of their data centres, and also give them a way to track the results of efficiency projects over time, said the EPA's Alexandra Sullivan, who described the program at the Green Grid data centre conference.

Data centres that take part will use an online tool that ranks their efficiency on a scale of 1 to 100. Those that score 75 or higher can request an audit from the EPA, which then awards the Energy Star certification.

The EPA has become increasingly active in data centres. It already has an Energy Star program for x86 servers, a program for storage equipment is underway, and it said it had started work on an Energy Star program for uninterruptable power supplies, or UPS systems.

Those programs are designed to help companies choose energy efficient products. The data centre programme is different in that it is more incentive-based. With public awareness about environmental issues so high, the EPA hopes companies will see an Energy Star rating as a potential marketing tool.

The EPA already rates the energy efficiency of 18 types of buildings, including offices and hospitals. The main criteria for those are floor space and hours of operation, but it needed a different system for data centers.

The measurement will be based largely on PUE (power unit efficiency), which measures the total power supplied to a data centre, divided by the amount that actually reaches IT equipment, rather than being lost to cooling systems and inefficient power supplies.

The EPA will also take into account the energy output from the UPS systems. That means that while data centres with good PUE scores will tend to get higher rankings, PUE will not be the only factor, Sullivan said.

The program is likely to stir some debate. Some attendees at the Green Grid event were surprised other criteria won't be included, such as whether a data centre is located in a cool or warm climate, or the level of redundancy it provides.

"You have to take the environment into account because it's easier to have a low PUE score if you're in a cold climate," said Don Klein, vice president of marketing and business development with Modius, which makes tools for measuring data centre energy use.

Not so, according to Sullivan. The EPA analyzed data from 108 data centres and determined that only the UPS output needs to be taken into account.

"We were surprised to find there weren't many operational variables that had a statistically significant impact on PUE," she said. "The variability is much more dependent on energy management practices than it is on characteristics."

The tier level might not be important because many data centres operate multiple tiers within a single facility, she said. And organisations that use fresh air to supplement air conditioners should still get better rankings, because fresh-air cooling tends to lower PUE scores.

Still, data centres will have the option to provide information about their level of redundancy, or tier level, "so we can analyse that data further if we feel we need to account for it in future models," Sullivan said.

In other words, the EPA will tweak its methods over time if it needs to.

Gary Murphy, principal with idGroup, a firm that designs data centres, called the programme "very useful." It will give data centre managers a way to show C-level executives, who are paying more attention to data centre energy bills, that they are running an efficient facility, he said.

But he also wondered if the EPA collected enough data for its analysis. "A hundred and eight data centres isn't a lot," he said.

The EPA will add the data centre criteria to its Portfolio Manager tool in June, and organisations that want to take part can enter their data to find their score.

The Energy Star program is also recognised in Europe. Andrew Fanara, who leads the program at the EPA, said China and India have also agreed "in principle" to use the EPA's system to rank products. Avoiding a patchwork of regional programs is important, he said, especially for multinational companies.