Power Usage Effectiveness
Power Usage Effectiveness (PUE) is an energy efficiency indicator for data centres. It is the ratio between the total energy consumed by the facility and the energy consumed by the IT equipment it hosts.
A PUE close to 1 indicates that little energy is spent on anything other than computing.
Limits
It does not measure computing efficiency. Replacing servers with others that consume twice as much but are equally under-used improves the PUE. A facility whose servers run at 5 % load can show an excellent PUE while wasting most of the energy it draws.
It ignores manufacturing. The indicator covers the use phase only.
It can shift the problem to water. Evaporative cooling lowers electricity use by consuming water, which the PUE does not see.
PUE should therefore be read alongside carbon and water indicators, and above all alongside actual server utilisation.
