A cooling system comprising: a ceiling plenum formed between a first ceiling and a second ceiling (103,105) of a building; a containment assembly disposed above at least one hot aisle formed by a plurality of rows of a plurality of server racks and extending through an aperture in the first ceiling, the containment assembly being configured to direct fluid from the hot aisle into the ceiling plenum; a fluid velocity sensor configured to measure velocity of fluid flowing in the hot aisle or the containment assembly; a temperature sensor configured to measure the temperature of the fluid flowing in the hot aisle or the containment assembly; at least one fan and heat exchanger assembly (1102,1104,1106); and a controller configured to adjust a speed of at least one fan of the at least one fan and heat exchanger assembly (1102,1104,1106) based on the measured temperature and velocity, wherein at least one fan of the at least one fan and heat exchanger assembly (1102,1104,1106) causes fluid to flow from the ceiling plenum, through at least one heat exchanger of the at least one fan and heat exchanger assembly (1102,1104,1106), and to the plurality of server racks; characterized in that the at least one fan and heat exchanger assembly (1102,1104,1106) includes a first row of a plurality of fan and heat exchanger assemblies and a second row of a plurality of fan and heat exchanger assemblies adjacent to the first row of the plurality of fan and heat exchanger assemblies; wherein the at least one heat exchanger assembly (1102,1104,1106) is disposed inside an outdoor cooling assembly outside of the building and adjacent to a wall of the building, wherein a fan and heat exchanger enclosure (1302, 1402) is housing the at least one heat exchanger assembly (1102,1104,1106); wherein the at least one fan causes fluid to flow through an aperture in the wall to the plurality of server racks. a ceiling plenum formed between a first ceiling and a second ceiling (103,105) of a building; a containment assembly disposed above at least one hot aisle formed by a plurality of rows of a plurality of server racks and extending through an aperture in the first ceiling, the containment assembly being configured to direct fluid from the hot aisle into the ceiling plenum; a fluid velocity sensor configured to measure velocity of fluid flowing in the hot aisle or the containment assembly; a temperature sensor configured to measure the temperature of the fluid flowing in the hot aisle or the containment assembly; at least one fan and heat exchanger assembly (1102,1104,1106); and a controller configured to adjust a speed of at least one fan of the at least one fan and heat exchanger assembly (1102,1104,1106) based on the measured temperature and velocity, wherein at least one fan of the at least one fan and heat exchanger assembly (1102,1104,1106) causes fluid to flow from the ceiling plenum, through at least one heat exchanger of the at least one fan and heat exchanger assembly (1102,1104,1106), and to the plurality of server racks; characterized in that the at least one fan and heat exchanger assembly (1102,1104,1106) includes a first row of a plurality of fan and heat exchanger assemblies and a second row of a plurality of fan and heat exchanger assemblies adjacent to the first row of the plurality of fan and heat exchanger assemblies; wherein the at least one heat exchanger assembly (1102,1104,1106) is disposed inside an outdoor cooling assembly outside of the building and adjacent to a wall of the building, wherein a fan and heat exchanger enclosure (1302, 1402) is housing the at least one heat exchanger assembly (1102,1104,1106); wherein the at least one fan causes fluid to flow through an aperture in the wall to the plurality of server racks.