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power usage effectiveness (PUE)

By Alexander S. Gillis

What is power usage effectiveness (PUE)?

Power usage effectiveness (PUE) is a metric used to determine the energy efficiency of a data center. PUE is determined by dividing the total amount of power entering a data center by the power used to run the IT equipment within it. PUE is expressed as a ratio, with overall efficiency improving as the quotient decreases toward 1.0.

Data center infrastructure and the processing power within it require a lot of energy, and data centers that do not operate efficiently will use more energy. Monitoring a metric like PUE is useful for benchmarking data center efficiency. Organizations and data center managers can use this metric once to measure their data center efficiency and then again to measure the effect of any changes made to the data center. This helps reduce power consumption and energy costs.

PUE was created by members of the Green Grid, an industry group focused on data center energy efficiency. According to the "Uptime Institute Annual Global Data Center Survey 2021," PUE and power consumption are among the top tracked sustainability methods. A similar benchmarking standard  recognized by the Green Grid is Data Center Infrastructure Efficiency, or DCiE.

How is PUE calculated?

The calculation of power usage effectiveness is total facility power/IT equipment energy = PUE. Total facility power is the amount of power the facility uses, which includes all data center hardware, power delivery components, cooling systems and lighting systems. IT equipment energy refers to the amount of energy that is used to power the storage and networking equipment as well as control equipment such as monitors and workstations.

PUE can be calculated using the following steps:   

  1. Measure energy use at the facility's utility meter. If the data center is in a mixed-use facility or office building, take a measurement only at the meter that is powering the data center. If it is not on a separate utility meter, estimate the amount of power being consumed by the non-data center portion of the building and remove it from the equation. A better way of doing this, however, is by using data center infrastructure management (DCIM) software. Instead of taking a trip to the utility meter and making an estimation, sensors are installed that collect real-time energy usage data for measuring PUE.
  2. Measure the IT equipment load after power conversion, switching and conditioning are completed. The most useful measurement point is at the power distribution units, which supply power to the computers and networking equipment. This measurement should represent the total power delivered to the server racks in the data center.
  3. Do the math. Once the measurements are collected, calculating PUE is just dividing total facility power by equipment energy.

Benefits and limitations of PUE

Benefits of power usage effectiveness include the following:

Some example limitations involved with data center PUE, however, include the following:

How can you lower PUE?

Steps to take in order to lower a power usage effectiveness ratio closer to 1.0 include the following:

Learn about more ways to reduce data center power consumption, including reducing CPU demands and addressing more cooling-related costs in this article.

29 Apr 2022

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