Techniques for cooling a data center include circulating an airflow, to a warm air plenum of a first module, from rows of racks that support a heat-generating electronic devices; warming the airflow circulated through the racks; circulating the warmed airflow through a warm air inlet of the warm air plenum that is adjacent an open side of the racks and to a warmed air outlet adjacent a data center volume above the racks; circulating the airflow, with a fan positioned in a second module positioned in the data center volume above the racks, through at least one cooling module to cool the warmed airflow, and into a human-occupiable workspace of the data center adjacent the racks; and diverting the warmed airflow with an airflow partition mounted in the data center volume above the racks and adjusted to interrupt the warmed airflow between the warmed air plenum and the human-occupiable workspace.