Abstract: An air cooler including a housing having an air inlet zone and an air outlet zone, a heat exchanger mounted in the housing and defining a first plurality of dry channels extending from the air inlet zone to the air outlet zone. Air is passed through the dry channels from the inlet zone to the outlet zone to be cooled and the cooled air constitutes a total airflow. The heat exchanger also defines a second plurality of moist channels each having an inlet and an outlet and alternating with the dry channels. The moist channels are intended for passing the air to be humidified from their inlets to their outlets and in cross-flow direction to the direction of the total airflow. The air to be humidified constitutes an auxiliary airflow which is formed from a part of the total airflow at the air outlet zone and is extracted from such a section of the air outlet zone, which is situated closer to the outlets of the moist channels than to their inlets.