Abstract: A system for cooling computer equipment in a data center. The system includes a raised floor defining a pressurized under-floor plenum; a computer room air conditioning unit disposed on the raised floor and having a hot air inlet and a cold air outlet, wherein the cold air outlet is in fluid communication with pressurized under-floor plenum; and a server cabinet housing server equipment and including a pressurized vertical plenum in fluid communication with under-floor plenum via an inlet duct. The server cabinet is configured to receive a cold air stream from the under-floor plenum via the inlet duct into the vertical plenum and draw the cold air across the server equipment to provide cooling without the use of external fans. The system may also include an inflatable airfoil damper assembly disposed within the inlet duct and configured to provide failsafe variable airflow to the vertical plenum within the server cabinet.