Data centres are the technological cathedrals of the 21st century. They concentrate a considerable heat load (5 to 30 kW/m²) that must be removed 24/7, 365 days a year. HVAC accounts for 30 to 40% of a data centre's total consumption — it is the number one lever for energy optimisation.
The PUE indicator
PUE (Power Usage Effectiveness) is the ratio of the total energy consumed by the data centre to the energy consumed by the IT equipment. A PUE of 1.0 would be perfect (all energy goes to the servers). In practice: PUE > 2.0 = poor, PUE 1.4-1.6 = standard, PUE < 1.3 = excellent. The best data centres achieve 1.1.
Cooling techniques
- • Hot/cold aisle containment: physical separation of hot air (discharged by servers) and cold air (supplied by CRAC/CRAH units). A 10-20% improvement in PUE.
- • Direct free cooling: using outdoor air when the temperature allows (< 22°C). Effective 60-80% of the time in northern France.
- • Indirect free cooling: air-to-air or air-to-water heat exchangers cool the room without mixing outdoor air with room air.
- • Liquid cooling: water is delivered directly to the racks or to cold plates on the processors. The future of high-density cooling.
- • Immersion cooling: servers are immersed in a dielectric fluid. An emerging technology for HPC (High Performance Computing).
The commissioning engineer's role
- • Commissioning CRAH (Computer Room Air Handler) units: checking airflow rates, temperatures and pressures.
- • Balancing air distribution beneath the raised floor: each perforated tile must deliver the correct airflow.
- • Redundancy testing: simulating a chiller failure to check automatic changeover.
- • PUE measurement: installing and calibrating energy meters.
- • Checking ASHRAE conditions: temperature 18-27°C, humidity 8-60% RH (A1 recommendations).
The data centre market in France is booming (+15% per year). Commissioning engineers specialising in this sector are in high demand and charge premium rates (€700-1,000 per day).