PUE standards for Power Usage Effectiveness and measures the energy efficiency of a server room or datacentre.
PUE = Total Facility Energy / IT Equipment Energy
The reciprocal measure of PUE is Data Center infrastructure Efficiency (DCiE)
DCIE = IT Equipment Power / Total Facility Power x 100%
PUE and DCiE were developed by the Green Grid (https://www.thegreengrid.org/) and are widely accepted energy efficiency measures that can also be used for bench marking.
It is important to note that PUE does not factor in sustainability and how the electricity used to power the facility is generated e.g. nuclear or renewable power sources. In addition, PUE does not consider energy reuse. Some larger datacentres may reuse heat created during the cooling process which in turns reduces the total energy consumption of the facility.