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The PUE Metric

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PUE Metric EquationWhat is PUE?

PUE (power usage effectiveness) is a measure of how efficiently a data center uses energy and how much is being used by the equipment. It is the ratio of total facilities energy (UPS systems, switchgear, generators, equipment, etc.) to IT equipment energy (storage, network equipment, KVM switches, monitors, etc.).

Data center power and cooling are two of the biggest issues that organizations face in controlling costs. Determining your data centers PUE can help improve operational efficiency and allows you to see where you can improve on the design and processes.

What are the levels PUE can be measured at?

The Green Grid provides a three-level approach to measure PUE. The table below shows the different levels for measuring. Each level provides increased measurement frequency and a more accurate measurement of energy usage.

The real difference in levels comes in the measurement period and the measurement placement. The measurement period increases for each level. Basic is performed monthly or weekly, intermediate is performed daily/hourly and the advanced is performed continuous, usually in 15-minute intervals or less. In terms of the measurement placement, each level provides a more accurate energy usage because measurements are being taken closer to the devices that consume the energy. At basic, the measurement is taken at the UPS outlet, at intermediate it is taken at the PDU outlet, and at advanced the measurement is taken at the IT equipment input.

PUE Metric Measurement Levels

Reporting PUE Results

While measuring PUE is a great way to see how energy efficient your data center is, it can also be confusing when reporting the results and comparing them to other data centers. There are various ways to calculate PUE results so this can make reporting results a concern. If a data center wants to compare itself to another data center’s results, it can be an unfair assessment. Data centers have individual capabilities and characteristics that make each one unique. This is why the Green Grid developed different levels and standards to follow when reporting PUE that can be adapted appropriately for each individual data center.

With proper reporting of the metrics, and by following guidelines the Green Grid put forth, data centers can get a real insight into long-term energy efficiency and how their center will handle future changes in IT power loads.

Calculate your PUE

References

“PUE: A Comprehensive Examination of the Metric.” The Green Grid. 2012. Accessed 25 March 2015. http://www.thegreengrid.org/~/media/WhitePapers/WP49-PUE%20A%20Comprehensive%20Examination%20of%20the%20Metric_v6.pdf?lang=en