What is Power Usage Effectiveness (PUE)?
Power Usage Effectiveness (PUE) is a data centre's total facility energy divided by the energy used by its IT equipment.
Why it matters
PUE shows how much energy a data centre spends on overhead, such as cooling, lighting and power distribution, for each unit of energy that reaches the IT equipment. A PUE of 1.0 would mean no overhead at all, so lower is better. The metric comes from The Green Grid and is standardised as ISO/IEC 30134-2.
Cloud providers publish their own PUE figures on different bases. AWS publishes for most regions over a calendar year, Azure for three large geographic groupings over a fiscal year, and Google Cloud by campus over a trailing twelve months. Figures are most comparable within one provider.
An example
Servers in a facility draw a certain amount of electricity. With a PUE above 1.0, the building draws more than that in total, because cooling and power conversion use energy too. Two identical workloads in regions with different PUE values therefore carry different electricity totals, before grid carbon intensity is even applied.
How Greenpixie measures it
Greenpixie multiplies IT electricity by the published PUE for each cloud region to get total electricity usage, which then drives usage emissions:
- AWS regions take the value AWS publishes for them
- Azure regions take their geographic grouping's value
- a Google Cloud region takes its campus's trailing twelve month value, or the mean where it matches several campuses
Where nothing published covers a region, Greenpixie assigns a value from other published figures and records which location it came from, and why.
Sources
- Greenpixie Cloud methodology: 3. Definitions
- Greenpixie Grid and Regions methodology: 7. Assessment and Calculation
- Greenpixie Grid and Regions methodology: 11. Outputs and Interpretation
- Greenpixie Cloud methodology: 7. Assessment and Calculation
- The Green Grid: PUE, A Comprehensive Examination of the Metric