US Patent 9091496 Controlling data center cooling

A data center cooling system includes a data center having electronic equipment that is supported in multiple racks; a cooling fluid source; multiple cooling units in the data center, where each cooling unit is configured to cool air warmed by a sub-set of the electronic equipment in the data center; multiple control valves, including a control valve associated with a particular cooling unit of the cooling units; and a controller arranged to modulate the control valve associated with a particular cooling unit, to open or close the control valve to substantially maintain an approach temperature set point of the particular cooling unit.