PUE (Power Usage Effectiveness) divides the data center’s total energy consumption (IT + cooling + losses) by the energy actually delivered to IT equipment. A PUE of 2.0 means one watt of cooling and losses rides along with every useful watt; recent sites target 1.2–1.4 (free cooling, aisle containment), while historical averages sit around 1.5–1.8.
Why it matters to you: when power is metered and re-billed, PUE multiplies your bill — 5 kVA of IT in a PUE 1.8 site consumes 9 billable kVA; at 1.3, only 6.5. Over a 3-year contract, the gap runs into thousands of euros.
Questions to ask: the measured annual PUE (not the design figure), how energy is re-billed, and renewable energy commitments — PUE has also become a CSR criterion in tenders.