A data center cooling system includes a plurality of server racks aligned within a row in a human-occupiable workspace of a data center, the server racks supporting a plurality of heat-generating computing devices; a warm air aisle positioned adjacent the server racks opposite the human-occupiable workspace and including a warm air inlet adjacent to a back side of the row of server racks and a warm air outlet in fluid communication with a warm air plenum; a plurality of cooling modules each including at least one fan and a cooling coil; and a controller to perform operations including controlling the plurality of fans in the plurality of cooling modules to operate at a specified fan speed, and controlling a plurality of valves fluidly coupled to the plurality of cooling coils in the plurality of cooling modules to modulate to a specified valve position.