Over the following pages we will be providing an introduction and definition to Power Usage Effectiveness (PUE) and its applications within data centre management. We will go on to address the strengths and weaknesses of this metric as a measure of data centre energy efficiency, to see if its reputation is justified. To conclude we will look at what we can learn from PUE and how assessment can help your business manage its long-term PUE by planning for change.

Topics included in this series include:

  1. What is Power Usage Effectiveness (PUE)?
  2. Understanding PUE measurement
  3. Long Term PUE
  4. The Character of PUE
  5. The Character of PUE Part 2
  6. Technological Maturity
  7. PUE and Location
  8. Summary

What is Power Usage Effectiveness (PUE)?

Power Usage Effectiveness is the predominant metric for establishing data centre energy efficiency. In recent years, PUE’s popularity has skyrocketed and it is now the most commonly used metric for identifying and measuring energy efficiency.

This rise looks set to continue with The Green Grid naming PUE as the industry's preferred energy efficiency metric worldwide. This decision is ratified by the US Department of Energy, the European Union through its Code of Conduct on Data Centres, the British Government through its adoption of the EU Code of Conduct and Japan's Ministry of Economy, Trade and Industry's Green Initiative, among others. It formalises PUE as a global guiding principle which the various nations and industry bodies hope will drive a universal understanding of data centre energy efficiency.

This all makes PUE sound very grand and confusing, however, the reality is quite different. Surprisingly for the measurement of such a complex infrastructure, PUE is quite a simple metric that establishes the relationship between the power supplied to a data centre and the power it consumes. It expresses this relationship as a numeric value which can then be used as a basis for understanding how efficiently the data centre consumes energy.

Mathematically PUE can be expressed as :

  PUE = Total Facility Power (TFP)
IT Equipment Power (ITEP)

ITEP and TFP components explained

IT Equipment Power is measured in kilowatts and includes all IT equipment used in the delivery of IT services and applications such as, servers, storage, switches, workstations, printers and any other service delivery equipment. This measurement is typically taken as the power delivered from the UPS infrastructure.

Total Facility Power is also measured in kilowatts. This includes the power consumed by all of the equipment included under the definition IT Equipment Power and all of the power used in the power delivery, cooling, air conditioning, and UPS. Lighting and other ancillary power is also included. This measurement is taken from the energy meter that controls the delivery of power to the entire data centre facility.

Use the PUE Calculator to work your own PUE calculation.

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