Power Usage Effectiveness (PUE) and How it Helps Businesses Increase Data Center Energy Efficiency

Data centers consume a vast amount of energy. According to the Natural Resource Defense Council, "data centers are one of the largest and fastest growing consumers of electricity in the United States. In 2013, U.S. data centers consumed an estimated 91 billion kilowatt-hours of electricity -- enough electricity to power all the households in New York City twice over -- and are on-track to reach 140 billion kilowatt-hours by 2020." Yikes.

While businesses like Google, Apple, Facebook and Amazon provide shining examples of ultra-efficient data centers, most corporate data centers have plenty of room for improvement, are generally much less efficient and taken together are responsible for the vast majority of data center energy consumption. One way for businesses to understand their data center's efficiency and identify areas for improvement, is to benchmark themselves against other, similar organizations utilizing the Power Usage Effectiveness standard.

Definition of Power Usage Effectiveness (PUE) 

PUE is an acronym for Power Usage Effectiveness and is becoming the accepted metric for describing the energy efficiency of data centers. In short PUE is measured like this:

PUE = Total Facility Energy / IT Equipment Energy where Total Facility Energy = Cooling + Power + Lighting + IT.

It is important to note that the Total Facility Energy calculation is related to energy dedicated to the data center's Physical Infrastructure not to the entire overall facility.

The lower your PUE score the better and a perfect score is 1.0 - meaning that your facility is 100% energy efficient. In essense, you want to use as much of your data center's energy on powering your IT equipment as you possibly can.

Components to Consider when Measuring your PUE

It is pretty easy to calculate your Total Facility Energy if your facility has a dedicated energy supply and meter running to your data center. If not, you need to do some calculations by looking at the various components you have in your data center that are drawing energy;
  • Power Distribution Equipment like UPS modules, Power Distribution Units (PDU's), generators, batteries, switchgear and lighting.
  • Cooling equipment like chillers, CRAC (Computer Room Air Conditioning) units, air handlers, pumps, fans and cooling towers.
  • IT equipment would include items like desktop and laptop computers, servers, storage devices, network equipment and supervisory equipment like KVM switches and monitors.
For more details you can check out The Green Grid an open industry consortion with the goal of improving the resource efficiency of data centers and business computing ecosystems.

What is a Good Power Usage Effectiveness Rating?

According to a recent survey by the Uptime Institute of more than 500 data centers, the average Power Usage Effectiveness rating for data centers is 1.8. That number is lower than in recent years from other sources and is probably indicative of an increased focus in the industry on energy management.
Google has recently announced that the average PUE in their data centers is 1.12 and in their best data center it is at an astounding 1.06 . Their message to the industry is that every business can get their PUE down into the 1's through a combination of best practices and equipment upgrades.
It should be noted that there are a number of professionals in the industry that don't believe PUE is an ideal metric for judging energy efficiency - or at least it's not the end-all-be-all. For example, according to Rich Miller at Data Center Knowledge, Microsoft recently removed all of the fans from their servers and are now letting their advanced air handlers manage that circulation task, but:
“If you look at the PUE, the server power went down because I removed the fans,” said Bhandarkar (Chief Architect for Microsoft Global Foundation Services, which designs and builds Microsoft’s data centers). “And the infrastructure power went up. So if I calculate my PUE, it got worse. But if I look at the overall energy efficiency, of how much work I’m getting done for the total power consumed, I end up ahead.”
Still, calculating and understanding your PUE provides you with a valuable, industry-accepted baseline for measuring the energy efficiency of your data center facility. After all, you can't control and improve what you can't measure. To learn more about how to calculate your PUE and improve the energy efficiency of your data centers, contact Carousel's Physical Infrastructure experts today. And stay tuned to Carousel Connect for future information about ways to improve your PUE and best practices you can take advantage of.

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