A cooling system includes one or more air channeling sub-systems that provide cooling air to electronic equipment, at least one heat removal sub-system that removes heat from the cooling air in at least one of the air channeling sub-systems, at least one temperature sensor measures a wet bulb temperature of outside air, and at least one controller. At least one of the air channeling sub-systems includes an outside air damper operable allow outside air into the air channeling sub-system. The at least one controller at least partially opens the outside air damper if a wet bulb temperature measured at the at least one temperature sensor drops to or below a predetermined temperature.