Power Usage Effectiveness � The Sequel - Page 3

Julius Neudorfer

U.S. EPA Energy Star for Data Center Program 

In an email exchange with Robert J. Meyers, of the U.S. EPA Energy Star for Data Center's program stated:

Since February 2010, EPA and DOE have co-chaired a committee that includes industry representation from the 7x24 Exchange, ASHRAE, the Green Grid, the Silicon Valley Leadership Group, the USGBC, and the Uptime Institute. 
Together, these groups issued a set of Guiding Principles for energy efficiency metrics in data centers, in February 2010.  In July of 2010, the Task Force issued a Version 1 PUE document, with expanded guidance of how to compute PUE in accordance with these guiding principles, in a standalone data center building.  In May 2011, the Task Force released a Version 2 PUE document, which expands on Version 1 to offer guidance for certain mixed use settings.

In a telephone interview with Alexandra Sullivan, technical development manager, Energy Star for Commercial Buildings, of the EPA's Energy Star program, noted:

The collective recommendations from this diverse task force seek to provide continuity in the way PUE is measured and reported. Consistency in PUE measurements will help improve energy efficiency by making it easier to track, report, and compare PUE values.

Moreover, in a related discussion, Sullivan stated that the Energy Star for Data Centers program now has 10 data centers that have successfully met the criterion and have received the Energy Star award. The Energy Star program also requires submission of PUE as annualized energy, not a power snapshot.


In a telephone interview with Michael K. Patterson, senior power and thermal architect, Intel Architecture Group, who represented ASHRAE on the task force, reflected that

ASHRAE's participation, as well as the 9.9 Technical Committee, helped to shape the cooling component energy measurements and values of the PUE 2 document, especially in the area of externally supplied chilled or condenser water, such as those found in data centers located in mixed use buildings. 

Moreover, Patterson felt that

The TC 9.9 Guidelines helped the data center industry understand how broader environmental conditions can significantly improve energy efficiency. It therefore allows the data center operators to better correlate the relationship between IT equipment reliability and a wider environmental envelope. This would allow data centers to operate their cooling systems more efficiently.

Uptime Institute

Even the Uptime Institute, which until recently had been fairly insular, has joined the task force. According to Matt Stansberry, director of content and publications, Uptime Institute:

Uptime Institute Executive Director Pitt Turner participated in the task force and provided feedback, but not a leadership role. Uptime Institute is currently focused on working with The Green Grid on its Data Center Maturity Model. Mark Acton, Network Director in EMEA has been working with Harqs Singh of The Green Grid to provide an industry test-bed for the organization's new Data Center Maturity Model (DCMM). The DCMM is a new framework for data center owners and operators to self-assess the environmental friendliness (maturity) of their data centers. Uptime Institute organized volunteers from the Network to help test this new industry benchmark. The volunteers will plot where their data centers fall on the Maturity Model and work with Uptime Institute and Green Grid to point out areas for improvement. Anonymous feedback from volunteers is planned to be published as a joint Uptime-Green Grid industry document.

Stansberry also shared the results of the institute's survey, which was released May 12th. Here are some interesting insights as to the current conditions and practices:

  • PUE has high adoption rates, but can lead to inaccurate reporting, (and) misrepresentation. Further adoption of carbon and water usage reporting metrics (WUE, CUE) will be important to the data center industry.
  • 55 percent of data centers are still at or below 70 [degrees] F.
  • Only twelve percent managing temperature as efficiently as possible (by measuring and controlling temperature at the air intake to the IT Equipment).
  • 40 percent still using return air temperature (at the CRAC/CRAH).

These Uptime survey results seem to help explain the reality of the situation and why a substantial portion (if not a majority) of data centers operate at or near a PUE of 2.0, which was revealed in the 2009 preliminary results of the EPA Energy Star survey gathered in the earlier stages of the program. 

The Bottom Line

The PUE metric may not be perfect and it is still evolving. Not all organizations subscribe to it, and some simply misuse it. Nonetheless, it has caused a much greater awareness of energy usage and efficiency in the data center industry. The advent PUE 2 as defined and now agreed to by the industry, as well as government entities, will hopefully increase broad-scale acceptance and use. Perhaps it will also reduce seemingly exaggerated efficiency claims by some and produce a more accurate and realistic picture of the data center environment.

So go ahead. Grab your favorite popcorn and get ready for a dose of reality on the road to going green while you download and read PUE Version 2.

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