A data center cooling system includes a server rack frame assembly that includes a plurality of bays defined along a lengthwise dimension of the frame assembly, each bay including a volume defined at least in part by a specified height that is orthogonal to the lengthwise dimension and a specified width that is parallel to the lengthwise dimension and sized to at least partially enclose at least one server rack configured to support a plurality of data center computing devices; and at least one cooling unit sized for a bay of the plurality of bays of the server rack frame assembly and configured to circulate a heated airflow from an open back side of the at least one server rack, cool the heated air, and circulate a cooling airflow through an open front side of the at least one server rack.