A data center comprising: a frame structure including a floor , walls , a roof , and a plurality of rows of equipment racks positioned within the frame structure , the rows of equipment racks being arranged parallel to one another and defining alternating hot aisles and cold aisles ; a common roof plenum disposed between the roof and a plurality of ceiling panels to contain and exhaust hot air via a common hot aisle plenum (external duct) from the data center; a common hot aisle plenum (external duct 84) in fluid communication with the common roof plenum that functions to receive exhausted hot air; at least one cooling unit in fluid communication with the common hot aisle plenum (external duct) , that functions to receive and configured to treat hot air delivered from the common hot aisle plenum (external duct) ; a common cold aisle plenum (external duct 88) in fluid communication with the at least one cooling unit that functions to receive cold air delivered from the at least one cooling unit ; another common cold aisle plenum (internal duct 90) in fluid communication with the common cold aisle plenum (external duct 88) that functions to provide cold air to the data center; wherein each hot aisle is contained within the frame structure ; wherein each cold aisle includes a plurality of the plurality of ceiling panels to contain air in the cold aisle , each ceiling panel being configured to extend between equipment racks of adjacent rows of equipment racks to define the cold aisle and configured to extend between equipment racks of a row of equipment racks and an aisle end wall to define the cold aisle , and wherein each row of equipment racks has a back adjacent the other common cold aisle plenum (internal duct 90), wherein the other common cold aisle plenum (internal duct 90) is configured to provide cool air to the cold aisles . a frame structure including a floor , walls , a roof , and a plurality of rows of equipment racks positioned within the frame structure , the rows of equipment racks being arranged parallel to one another and defining alternating hot aisles and cold aisles ; a common roof plenum disposed between the roof and a plurality of ceiling panels to contain and exhaust hot air via a common hot aisle plenum (external duct) from the data center; a common hot aisle plenum (external duct 84) in fluid communication with the common roof plenum that functions to receive exhausted hot air; at least one cooling unit in fluid communication with the common hot aisle plenum (external duct) , that functions to receive and configured to treat hot air delivered from the common hot aisle plenum (external duct) ; a common cold aisle plenum (external duct 88) in fluid communication with the at least one cooling unit that functions to receive cold air delivered from the at least one cooling unit ; another common cold aisle plenum (internal duct 90) in fluid communication with the common cold aisle plenum (external duct 88) that functions to provide cold air to the data center; wherein each hot aisle is contained within the frame structure ; wherein each cold aisle includes a plurality of the plurality of ceiling panels to contain air in the cold aisle , each ceiling panel being configured to extend between equipment racks of adjacent rows of equipment racks to define the cold aisle and configured to extend between equipment racks of a row of equipment racks and an aisle end wall to define the cold aisle , and wherein each row of equipment racks has a back adjacent the other common cold aisle plenum (internal duct 90), wherein the other common cold aisle plenum (internal duct 90) is configured to provide cool air to the cold aisles . <EOS>