PUE (Power Usage Effectiveness) measures how much energy goes to IT vs cooling and overhead. Lower is better. Many tier-III facilities use efficient cooling and renewable power. Ask providers about their sustainability metrics.
What is PUE
- PUE = Total facility power / IT power. A PUE of 1.5 means for every 1 kW used by servers, 0.5 kW goes to cooling, lighting, and other overhead.
- Lower is better: 1.2–1.5 is common for modern facilities; below 1.2 is excellent. Older DCs can be 2.0 or higher.
- Improvements: Efficient cooling (free cooling, hot/cold aisles, containment), better UPS and distribution, and right-sized capacity.
Renewable energy and cooling
- Renewables: Some providers run on 100% renewable or buy RECs (Renewable Energy Certificates). Ask for a sustainability report or carbon commitment.
- Cooling: Air conditioning is a big cost; efficient designs (e.g. evaporative, liquid cooling for high-density) reduce PUE and cost.
- Tier-III: Redundant power and cooling improve availability; design can also improve efficiency compared to single-path legacy sites.
What to ask providers
- PUE (average or design) and whether it is audited.
- Renewable % and how it is achieved (on-site, RECs, PPAs).
- Carbon goals and reporting (e.g. GHG protocol, Science Based Targets).
Summary
PUE measures efficiency (IT power vs total). Lower PUE and renewable energy reduce cost and environmental impact. Ask providers for PUE, renewables, and carbon reporting.
