Abstract: Cooling fluid pressure within a plenum of a cooling system is controlled by activating the cooling system, sensing a plurality of cooling fluid pressures at a plurality of respective locations within the plenum, determining whether pressure differences between the plurality of sensed cooling fluid pressures are within a predetermined pressure differential, and modulating a variable volume device in response to the pressure differences being outside the predetermined pressure differential. The cooling system is configured to cool racks in a data center and includes a cooling device in fluid communication with the plenum. The plenum is in fluid communication with a vent configured to supply cooling fluid to the racks. The variable volume device is configured to control a flow resistance of cooling fluid within the plenum and is positioned between the plenum and the vent.