The Green Grid consortium, which developed the widely used PUE metric for measuring energy efficiency in data centers, is developing two more metrics to address carbon emissions and water usage, it said Thursday.

A paper describing the new CUE, or Carbon Usage Effectiveness, metric has been posted on The Green Grid's website. Materials describing the WUE, or Water Usage Effectiveness, metric will be posted by March next year it said.

PUE, or Power Usage Effectiveness, has been adopted widely in the past few years. Google and Microsoft often boast about their PUE numbers, and more enterprises are starting to calculate their PUE as a starting point for energy efficiency projects.

PUE measures how much of the total electricity used by a data centre goes to the IT equipment, as opposed to being lost on cooling systems or inefficient power supplies.

Carbon efficiency

CUE is intended to help managers determine the amount of greenhouse gas emissions generated in delivering work from the IT gear in a data centre facility.

It will measure only emissions from operations, and not greenhouse gases "embedded" in the data centre as a result of the manufacturing of servers or building materials, said Larry Vertal, executive director of The Green Grid.

To keep things manageable, the first version of the CUE metric will only take into account what the World Resources Institute describes as "Scope 1" and "Scope 2" emissions, Vertal said.

Scope 1 covers the direct emissions of the data centre, primarily from backup power generators, while Scope 2 refers to the emissions of the power utility. Scope 3, "everything else," would include the emissions of the mining and manufacturing operations that supply fuel and equipment to the power utility.

At least in the US, information is readily available about utilities' generating mix whether they use coal, nuclear or renewables, so businesses can plan where to build future data centres for minimum impact, Vertal said. Compared to PUE, CUE is very much a forward-looking metric, he said.

As for WUE, it is intended help managers determine the amount of water used by the facility, and the amount used to deliver work from IT operations.

However, this metric still requires more work for two reasons, said Vertal: Data on utilities' water usage is much harder to come by, for one thing, and for another the quality of water used can vary and that must be taken into account.

"If you're doing evaporative cooling using drinking water, or partly treated river water, or sewage with particulate matter removed, those waters have different values," he said.

Environmental pressure

Data centers are under pressure to be more environmentally responsible. Greenpeace has targeted cloud computing as a source of global warming, and in Europe there are already carbon taxes for big energy consumers.

Most data centres use vast amounts of water for cooling, making it another logical area to tackle.

The issue jumped to the forefront in the US after a report to Congress estimated that data centres accounted for 1.5 percent of total US energy consumption, and that the figure could double by 2011.

The new metrics will be discussed at The Green Grid's Technical Forum next March.

The consortium is comprised mostly of IT vendors, including Microsoft, Oracle and HP, as well as a few end user companies such as Target which are trying to come up with ways to improve data centre efficiency.