What is PUE and why do data centre operators quote it?
Power usage effectiveness is total electricity used by a data centre divided by the electricity that reaches the computers. The closer to 1.0, the less is spent on cooling and losses.
A data centre buys electricity for two things: running servers, and everything else. Everything else is mostly cooling, plus power conversion losses and lighting. PUE is the ratio between the total and the part that reaches the IT equipment.
A PUE of 2.0 means that for every watt of computing, another watt is spent keeping the building running. A PUE of 1.2 means the overhead is only 20%. The large cloud companies report figures near 1.1 for their newest sites. The industry average in Uptime Institute surveys has stayed between about 1.5 and 1.6 for years.
The figure has become a commercial matter because AI hardware runs hotter and denser than older servers. Operators are moving from air to liquid cooling, and some governments now set a maximum PUE as a condition for a building permit or a grid connection.
- Formula
- Total facility energy divided by IT equipment energy
- Industry average
- About 1.5 to 1.6 (Uptime Institute surveys)
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