Data Center Cooling and Mechanical Systems
Heat Removal Fundamentals
Cooling design starts with heat load: IT equipment, lighting, people, and envelope gains. Understand sensible vs. latent load, airflow (CFM or m³/s), temperature differential across the rack, and the relationship between airflow and cooling capacity. Know that modern IT equipment tolerates wider temperature and humidity ranges per ASHRAE guidance, enabling economizers.
Cooling Architectures
Master CRAC/CRAH units, chilled water vs. direct expansion, air-side and water-side economizers, and emerging liquid cooling (direct-to-chip, immersion) for high-density racks. Understand containment (hot or cold aisle), raised-floor plenum behavior, and the role of variable-speed fans and controls. Know PUE and how cooling choices affect it.
Concepts to Master
- Airflow management: blanking panels, grommets, sealed cable openings.
- Temperature and humidity control bands and condensation risk.
- Redundancy in cooling: N+1 chillers, pumps, and CRAH units.
- Economizer hours and climate dependence.
- Liquid cooling for racks exceeding air-cooling limits.
Common Traps
Questions often test whether you know that containment improves efficiency but requires careful fire suppression integration. Another trap: assuming colder is always better - overcooling wastes energy and can cause humidity issues. Watch for distractors that ignore airflow bypass and recirculation.
Worked Example / Rule of Thumb
If a rack dissipates 10 kW and the design air temperature rise is 10°C, required airflow is roughly proportional to load divided by temperature rise; higher ΔT means less airflow. Rule of thumb: seal every opening, blank every empty U, and design containment before adding cooling capacity - airflow fixes are cheaper than more chillers.