What is PUE?
Power usage effectivenessReviewed
Power usage effectiveness (PUE) is the standard measure of data center energy efficiency: the total energy a facility uses divided by the energy used by its IT equipment. A PUE of 1.0 would mean every kilowatt-hour reaches the servers, storage and network; a PUE of 1.5 means half as much again is spent on cooling, power conversion and lighting.
- FormulaTotal facility energy ÷ IT energy
- Introduced byThe Green Grid, 2007
- StandardISO/IEC 30134-2
- Ideal value1.0
01
What PUE does
PUE shows how much overhead a facility adds to its computing load. It is used to compare a site with itself over time, to set design targets for new halls, and increasingly in regulation and customer reporting.
Because it is a ratio, PUE moves with the weather, the season and the IT load: a half-empty hall usually has a worse PUE than a full one, because cooling and losses do not shrink in proportion.
Key functions
- Tracks cooling and power-chain overhead
- Compares a site against itself over time
- Sets design targets for new capacity
- Supports efficiency reporting
- Pairs with WUE for water and CUE for carbon
- Shows the effect of cooling changes
02
Why PUE matters
For a large facility, the gap between a PUE of 1.6 and 1.2 is a large share of the power bill and of the grid capacity the site needs. With power now the main limit on data center growth, overhead is capacity that cannot go to compute.
Reporting is also tightening. The EU’s Energy Efficiency Directive requires larger data centers to report energy performance including PUE, and customers increasingly ask for it in contracts.
03
How PUE works
PUE is calculated over a period, ideally a full year, as total facility energy divided by IT equipment energy. Total facility energy is measured at the utility meter. IT energy can be measured at different points: the UPS output, the PDU output or the IT equipment input; measuring closer to the equipment gives a more accurate and usually higher figure.
ISO/IEC 30134-2 defines these measurement categories so figures can be compared fairly. A PUE quoted without its period and measurement point is hard to interpret, and a single instantaneous reading can look much better than the annual figure.
01
Utility meter
Total facility energy
02
Cooling and losses
Overhead
03
UPS, PDU or rack
IT energy
04
PUE
Total ÷ IT over a period
04
How PUE feeds Voltra
Voltra models a data hall’s electrical chain from the utility service through UPS and PDU to each rack and reads server power over Redfish, so total facility power and IT power come from the same model and the same time base. Reports are built from those readings.
05
Frequently asked questions
It depends on climate, design and load. Uptime Institute’s annual surveys have put the industry average at around 1.5 to 1.6 for several years, while new large facilities are often designed for 1.2 to 1.3 or lower.
Divide the total energy the facility used over a period by the energy its IT equipment used over the same period. For example, 15 GWh total and 10 GWh IT gives a PUE of 1.5.
Data center infrastructure efficiency, the inverse of PUE expressed as a percentage. A PUE of 1.5 is a DCiE of about 67%.
Not on its own. PUE ignores how efficiently the IT equipment does its work, and a site can lower PUE by using more water for cooling. Metrics such as WUE (water) and CUE (carbon) fill in some of the picture.
