Density changes the problem
A hall designed around a few kilowatts per rack behaves very differently at twenty or more. Containment, whether hot aisle or cold aisle, stops being an efficiency refinement and becomes a functional requirement. Bypass and recirculation that were tolerable at low density become failure modes at high density.
Airflow is the constraint, not cooling capacity
Plant capacity is rarely the limit. Delivering the air to the rack face and returning it without mixing usually is. Underfloor obstruction, poorly placed grilles and unsealed cabinet apertures waste capacity that is already paid for.
Verification has to model failure, not just normal operation
A hall that performs well with all units running says nothing about performance when one fails or during a transfer to standby power. Meaningful testing includes unit failure scenarios, transfer transients and the thermal ride-through the design assumes.
Instrumentation earns its cost
Rack inlet temperature monitoring at representative positions turns cooling from an assumption into a managed parameter, and provides the evidence needed before increasing density in an existing hall.
