The problem with the (use of) PUE in the Data Center industry

Montage-data-centers.jpg

I had mentioned in a previous post on reporting and use of PUE, including the terms iPUE, PUE3, dPUE etc ( https://www.linkedin.com/pulse/data-center-resource-efficiency-pue-isoiec-30134-james-soh-%E8%8B%8F%E6%97%AD%E6%B1%9F).

Like how Tier / Facility Class / Rated are being mentioned fuzzily in the industry, having not make clear whether it is designed according to which standard or certified or not, of which the confusion is not helping the potential clients and the whole industry. Just to clarify, I take no stand against any data center saying that its facility is designed in accordance to a particular standard given that any potential client should and will make detail review and audit of the facility before committing to a co-location deal.

The issue that I like to highlight in this post, is the use of designed PUE (dPUE) instead of PUE in the way it is used in a manner to market or even set policy. dPUE itself is subject to estimation (as per example case in ISO 30134-2) and imprecise. The actual PUE3 versus dPUE can have a huge gap given the IT load profile will normally not ramp up to near 100% for any new data center facility.

This encourages the owner of yet-to-be-built data center to claim a low dPUE. You know, it is an estimate, who is it to say the figure of 1.13 is wrong? You want to check my calculations? Talk to my design consultants who are the ones that work out that number (at the insistence of me to assume the best case situation to come up with a low dPUE).

The announced ban by Beijing for new data center with PUE of 1.5 or above really meant designed PUE. Given that it is a designed PUE, a lot can go into estimating a low dPUE. Who is going to shut-off the power after the data center facility is designed, equipment selected, built and operating at well below full capacity thus yielding a bad actual interim PUE? There are many ways to go about to make the dPUE figure works to your advantage. See reference 1.

You may ignore ancillary power usage or give a very low predicted power usage in the mechanical load or cite the most ideal power efficient chiller in the design but choose a not the most efficient chiller when you decide to purchase the actual equipment. Or you decide to base your dPUE on PUE1 or PUE2 way of calculating the dPUE which makes it look slightly better. They all add (or minus) up.

pue-at-design-load-chart-2

Credit: CGG Facilities. http://www.ccgfacilities.com/insight/detail.aspx?ID=18

From my experience of operating and auditing more than a dozen data centers, I have seen very crude designed PUE estimation and some better ones.

The thing is that the designed PUE always looks too good and it stems from:

  • Not including some of the data center infrastructure losses
  • Not including electricity losses in the cables (3%)
  • Tolerance of installed equipment performing to factory specifications
  • Estimation using PUE1 situation, i.e. at UPS output whereas PUE2 or PUE3 is the recommended way
  • Different environmental conditions over 12 months in a real data center will be sub-optimal

A friend of mine who works in the data center co-location service provider laments that their honesty has given them a lower category in a green data center award versus others in the same city that claim lower dPUE figures and got higher awards. It may not be completely due to the lower dPUE figures, but it play a part.

The clients are not fools and the data center colocation service provider that claims such low dPUE will find it tougher to negotiate co-location service contracts as the power bill recovery in some countries are tied to the actual PUE but related to the dPUE when closer to full utilization. This will eat into their profits.

Ultimately, it is the real PUE3 that measures over a period of 365 days at current client IT power load that matters, and a 100% leased out co-location data center which meant full endorsement by the clients. Nothing speaks better that ka-chin at the cash registers, no amount of bill board outside will take money out of wallets of potential clients. It is how the design, equipment selection, measurement and reporting, running a tight operations, continuous monitoring and enhancement, people that all combines into having a well-run and well respected data center facility with a happy clientele that grows the co-location business. Playing with dPUE gets some attention, but delivering the service consistently and having clients that take up more of your data center space is the indicator of healthy data center business.

It is my hope that awards in energy efficient data center shall be based on actual PUE, rather than designed PUE.

Reference:

  1. http://www.ccgfacilities.com/insight/detail.aspx?ID=18
  2. https://www.greenbiz.com/article/new-efficiency-standard-challenges-data-center-status-quo
  3. http://www.datacenterknowledge.com/archives/2009/07/13/pue-and-marketing-mischief/
  4. ISO/IEC 30134-2    Part 2, Power Usage Effectiveness (“PUE”) – http://www.iso.org/iso/home/store/catalogue_tc/catalogue_tc_browse.htm?commid=654019
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The problem with the (use of) PUE in the Data Center industry

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