Move Over PUE - Part II

Julius Neudorfer

So maybe EUE is PUE after all, but different. On Nov. 12, the EPA released the finalized direction for its new Energy Star for Data Centers program. This is the followup to the Sept. 29 presentation, which I first summarized last month.

As the EPA's Energy Star for Data Centers program progresses toward finalization, it has decided to base the EUE metric (Energy Usage Efficiency) on The Green Grid's PUE (Power Usage Efficiency) metric, but with a twist. Instead of measuring power in KW, it will be using 'energy' as measured in BTUs or more specifically, millions of  BTUs, used over a 12- (or 11-) month period. BTU, not KW -- confused?  What, your data center metering (assuming that you are doing metering) only measures volts, amps, KVA and KW? You aren't burning gas, oil or coal as the primary source of electricity?

On the face of it, the basic EUE formula could not be any simpler: Total IT energy/total source energy. What could be simpler? Don't you just love it? Just when you were beginning to get the hang of measuring and calculating your PUE.

Just a little insight: According to the EPA, an average metric ton of coal has 22.68 million BTUs, which is then burned in a power plant to produce electricity. Don't worry about all the details, the EPA will figure out how much 'source energy' the power plant is using to generate the electricity for you. Oh, and by the way, it also will calculate for the power lost in the transmission lines.

Perhaps this will spur the development of fuel cell technology, as well as, solar, wind, hydro and perhaps nuclear-powered data centers. But for now, data center operators not only need to think in terms of 'tons' of cooling they need, they also need to think about how many tons of coal are being burned in a power plant they don't control. 

In fact, the study revealed that many data centers in the original sample were not able to accurately measure IT energy at the rack or PDU level, so the EPA settled for the UPS output as the IT energy. In effect, it's ignoring all the distribution efficiency (or inefficiencies) that could be part of data center's possible improvement or design.

At the Sept; 29 presentation, the final reference model was going to be based on the data collected from the original 108 sample data centers (both dedicated and those located in mixed-use building). At the Nov. 12 presentation, it had reduced it down to only the 61 dedicated data centers that will now be used as the 'standard' reference model for several years to come. Moreover, it also found that they could not find any significant energy-efficiency difference related to climate or the use of economizers for cooling, so it will not use this in any of the calculations or ratings.

The fairest part of their new standard is that it does base the EUE rating on total energy used on an annualized basis. Unlike PUE, which could allow just picking a snapshot for the power measurement (like 3 a.m. in the middle of January in Minnesota at -5�F, just running on outside air with the chillers off), PUE uses 'power'-'energy' is power over time, in effect the difference between KW and KWH.

So while the intention of all parties concerned may have been to define a 'data collection strategy' and define a metric for energy efficiency in the data center, they may have just introduced a complication to a simple problem.  If they simply used 'IT KWH' / 'Total KWH' as measured over a 12-month period, everyone in the data center world could understand, measure and relate to it. Instead, the EPA has decided to base the metric on 'source energy' in BTUs at the power plant, something that data center personnel do not readily understand nor, more importantly, control.


So far this EUE program is voluntary, but like many government programs, it begs the question -- if there are not enough 'volunteers," will the EPA ask Congress to consider mandating a data center CAF� automotive-style mileage standard for data centers? And of course if that happens, perhaps it could also ask the DOT to look into creating some 'crash' standards for computers as well. 

So don't look now, but if the EPA's program sets the new standard, then the 'data center of the future' may be one that is based on on-site co-generation and uses the utility grid only as the backup source.

So keep watching this blog for updates and the EPA Web site for more details as it finalizes Energy Star for Data Center program, which is scheduled to go into effect in April 2010.

My efficiency advice for the moment: Keep your hot aisles hot and your cold aisles cool (or at least below 80�F).



Add Comment      Leave a comment on this blog post
Jan 6, 2010 1:01 AM Anonymous Anonymous  says:
We should expect some confusion over UPS output, too. I have seen people use UPS input in their PUE calculations. Reply
Sep 19, 2011 4:09 PM recuperer son ex recuperer son ex  says:
Keep up the fantastic work, I read few articles on this website and I believe that your web blog is rattling interesting and holds sets of fantastic information. Reply

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