Why PUE Level 3 Monitoring is Within Reach

Posted by Neche Veyssal on March 24, 2021

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An improved (lower) PUE may be misleading since it can result from inefficiencies in the power consumed by IT equipment, which merely increases the denominator. A lower PUE is generally better than a higher one, but it is possible to implement measures that reduce data-center-energy consumption, yet actually increase your PUE. For example, if you were to replace older, less efficient servers with more efficient ones, eliminate ghost servers, turn off servers that were idle during the night, or employ server virtualization, the net result would be power reduction, but your PUE would actually increase.

Reducing Energy Consumption: More Than Just Improving Your PUE Metric

The Green Grid defines three levels of PUE: Basic or Level 1, Intermediate or Level 2, and Advanced or Level 3. Many industry analysts recommend measuring IT-power consumption at the Intermediate or Level 2, (i.e., at the PDU level). While it is true that PDU-level-power consumption will provide the denominator needed to calculate PUE, this information alone is likely insufficient to drive the best efficiency improvement decisions. 

Here are the three PUE tracking levels according to The Green Grid:

• Level One (Basic): IT-equipment power is measured at the UPS, and total-facility power is based on measurements at the input-power source. Measurement frequency is weekly to monthly.
• Level Two (Intermediate): IT-equipment power is measured at the PDU, and total-facility power is based on measurements at the input-power source less any shared HVAC load. Measurement frequency is daily.
• Level Three (Advanced): IT-equipment power is measured at the server, and total-facility power is data-center-input powerless shared HVAC plus building, lighting, and security-power loads. Measurement frequency is continuous.

The detailed IT load data from Level 3 provides the granularity of information to reduce energy consumption, not just improve the PUE metric. Clearly, PUE (and its inverse, DCiE) becomes a more useful beacon once you have built efficiency into the IT-equipment performance; to do that you will want the granular power-usage data for the Advanced, Level 3 PUE metric. Then you can attack the numerator and squeeze inefficiencies out of the infrastructure.

The Xerus Technology Platform

With Legrand intelligent-rack power distribution units (PDUs), from Server Technology and Legrand, continuous server-level power monitoring is built-in via the Xerus technology platform.

Contact us here at Raritan or Server Technology to learn more about our intelligent PDUs and how they can support your PUE and power-monitoring needs. 

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