ERE (Energy Reuse Effectiveness)

Energy Reuse Effectiveness (ERE) is a data center sustainability metric, developed by The Green Grid, that measures how much of a facility's total energy is reused elsewhere — for district heating, greenhouses, or adjacent buildings — rather than measuring pure efficiency the way PUE does. It is calculated as (total facility energy minus reused energy) divided by IT equipment energy: an ERE of 0 means all incoming energy is productively reused outside the data center's boundary, while ERE equals PUE when no reuse occurs. The metric complements PUE and CUE by explicitly capturing waste-heat-reuse schemes, which have become more common as Nordic and Northern European operators pipe server heat into municipal district-heating networks, partly driven by EU Energy Efficiency Directive reporting pressure.