An adiabatic process is a process in which the energy content (enthalpy) of the air/moisture mixture does not change.
Direct cooling means that the supply air comes into direct contact with water or a wet surface.
Evaporation of water
Water has a latent heat of vaporization of 2501 kJ/kg at 0 °C. As such, for example, adiabatic evaporation of water at a rate of 1 L/h decreases the sensible enthalpy of the air by 695 W (air cools down) and increases the latent enthalpy by the same amount (air becomes more humid).
Indirect cooling means that the supply air does not come into contact with water or a wet surface.
Indirect/direct cooling is a combination of indirect cooling and direct cooling.
Indirect/direct evaporative cooling
Indirect/direct evaporative cooling is a combination of either indirect evaporative cooling with direct evaporative cooling or indirect (non-evaporative) cooling with direct evaporative cooling.
Wet bulb efficiency
The ratio of the actual achieved temperature difference between the inlet and outlet air to the temperature difference that would have been achieved when the inlet air is cooled to the wet bulb temperature. Also named "wet bulb effectiveness".