Why keep cold aisle doors closed?

• A. Blocks RFID signals.
• B. Provides physical security.
• C. Reduces cable length.
• D. Maintains pressure/airflow, improves cooling efficiency, and protects thermal budget.

Answer: (D)

Keeping cold aisle doors closed centers on controlling where the cooling air goes. When the cold aisle is sealed, cold supply air is kept in close proximity to the server intakes and is prevented from mixing with the hot exhaust air in the adjacent aisle. This creates a stable, high-pressure stream of cold air that moves efficiently through the equipment and toward the cooling return path.

That containment improves cooling efficiency because more of the air that the cooling system pushes actually reaches the server components instead of leaking into the hot aisle. With less mixing, the inlet temperatures remain lower, so servers can run cooler without the fans having to work harder, which also helps reduce energy use. It also protects the thermal budget by keeping the data center within its designed temperature and cooling capacity, avoiding hotspots and unnecessary cooling demand.

If the doors were left open, cold and hot air would mix, breaking the effective separation, raising inlet temperatures, increasing energy consumption, and risking thermal budget overruns.