Heat rejection apparatus

A heat rejection apparatus comprising:

• a heat exchanger;
• an adiabatic medium;
• a liquid distribution system configured to distribute liquid to the adiabatic medium to wet the adiabatic medium;
• an airflow generator operable to cause an airflow through the adiabatic medium and toward the heat exchanger;
• an air condition sensor configured to detect a variable indicative of adiabatic cooling of the airflow by the adiabatic medium;
• and
• a controller operably connected to the liquid distribution system, the airflow generator, and the air condition sensor, the controller configured to:
• determine a saturation efficiency of the adiabatic medium based at least in part on the variable associated with the adiabatic cooling of the airflow by the adiabatic medium;
• and
• operate the liquid distribution system to distribute liquid to the adiabatic medium based at least in part on the determined saturation efficiency to achieve a target saturation efficiency of the adiabatic medium.