Cooling a data center

A method for controlling a plurality of cooling modules each comprising at least one fan and a cooling coil positioned to circulate a cooling airflow from a human-occupiable workspace, through a plurality of server racks, and to a warm air aisle positioned adjacent the server racks opposite the human-occupiable workspace and comprising 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, the method comprising:

• sensing a differential pressure calculated across the warm air aisle;
• controlling, with a single controller electrically and communicably coupled to each of the plurality of cooling modules in a serial arrangement, the plurality of fans in the plurality of cooling modules based on the differential pressure to operate at a specified fan speed;
• sensing a plurality of temperatures in the plurality of cooling modules;
• 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 based at least in part on the plurality of temperatures;
• and
• providing power to the single controller from one of the plurality of cooling modules through a direct current (DC) control power bus independently of a loss of power to the other cooling modules of the plurality of cooling modules.