Green Grid Updates PUE with 4 New Flavors to Boost Accuracy

Green Grid Updates PUE with 4 New Flavors to Boost Accuracy

IT Industry consortium The Green Grid has released a new, updated set of guidelines for calculating the Power Usage Effectiveness ratio, one that aims to make the standard both more accurate and more widely adopted.

PUE has quickly become the de facto global standard for measuring data center energy efficiency, in part because the calculation was so simple: Divide total power used by your data center by the power going to hardware (rather than to lighting, cooling, or other non-computing operations), and you have a snapshot of how efficient your facility is.

green grid white paper

But the simplicity of measuring PUE has also worked against it, with experts levying criticisms of manipulation for greenwashing purposes as well as the difficulty of comparing data centers accurately.

In response to these concerns, The Green Grid worked with a number of groups, including the EPA's Energy Star program, ASHRAE, the Silicon Valley Leadership Group and others, to refine and expand the standard.

The result is a four-level PUE that allows companies to choose the measurement approach that most meets their needs, and allows customers to more accurately gauge just how efficient a data center is.

In a white paper published last week, the Green Grid laid out the four categories, and what they measure. The chart below sums up the findings, and download the full paper from to learn more.


green guard figure 1


The new categories gradually increase in accuracy, from Category 0 data centers that simply measure peak load for 12 months at the UPS system's output to Category 3 data centers, which measure a 12-month total kilowatt-hour reading at the point of connection of IT hardware. Category 3 is the most accurate, the Green Grid says, because it "remov[es] all impact of losses associated with electrical distribution components and non-IT related devices, e.g., rack mounted fans, etc."

In developing the new categories, The Green Grid and its partners also incorporated forward-looking green IT practices into the PUE calculation. For instance, in addition to weighting different types of energy for power and cooling, the standard also includes notes on calculating PUE for data centers powered by renewable energy and for data centers that reuse waste heat either within the facility or outside the compute center.

The white paper, "Recommendations for Measuring and Reporting Overall Data Center Efficiency," is available for download from; for more information about The Green Grid's work, visit

Data Center photo CC-licensed by SunGardAvailabilitySvcs.