EPA to use PUE in Data Center Energy Star

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"PUE will be the basis for the initial ENERGY STAR rating for data centers, though the rating will be expressed on a 1-100 scale as is done for all other building types - where each point on the scale represents 1 percentile," said Mike Zatz, Chief of the Market Sectors Group for ENERGY STAR. "PUE was chosen as an initial basis because at this time there is no industry consensus on a metric that would incorporate some measure of the work done by the facility." The rating will be based on the average PUE ratio for the facility, calculated from 12 months of actual measured data.

The EPA plans to implement Energy Star for Data Centers using the PUE-based standard, and then introduce a more comprehensive rating down the road. "If the industry is able to reach some type of consensus, our plan is to modify the rating in the future to be based on a comparison of energy used per unit of useful work or work output," said Zatz. A similar two-phase approach is being used for the Energy Star for Enterprise Servers ratings, which will take effect in the next few weeks.

The EPA's ultimate goal is to refine the rating to reflect metrics that compare the output or work from the data center with its energy use. The Green Grid recently began considering proposals for methods to measure the "useful work" of a data center.

The PUE metric (PDF) compares a facility’s total power usage to the amount of power used by the IT equipment, revealing how much is lost in distribution and conversion. An average PUE of 2.0 indicates that the IT equipment uses about 50 percent of the power to the building.

Energy Star was introduced by EPA in 1992 as a voluntary program to reduce greenhouse gas emissions through energy efficiency. The Energy Star label can be found on more than 50 different kinds of products, new homes and commercial and industrial buildings.

Developing a facility-level rating would allow companies to track the energy efficiency of multiple data centers, and offer a basis for comparing the efficiency of different data centers.

In 2007 the EPA began looking for more than 125 organizations with data centers of at least 1,000 square feet to voluntarily provide energy usage data that will help develop the Energy Star Data Center Infrastructure Rating. Participants must collect 12 consecutive months of energy use data for its IT equipment and building (whole building if a stand-alone facility, or data center portion only if within a larger building).

The program was initially scheduled to start last June 1, but was delayed when just 50 data centers agreed to take part. After additional appeals for participation, 215 data centers agreed to submit data and the program launched a month late. Last month the EPA said just 110 data centers have shared their energy data.