Indirect/Direct Evaporative cooling unit also known as Two-stage Air Washer Unit, uses both indirect and direct cooling techniques to cool the air.
In Two Stage Evaporative Cooling system, the first stage is Indirect Evaporative cooling. In Indirect Evaporative cooling stage(IEC) the water and hot air travel in different channels. Water and hot air do not come in direct contact with each other. This is why it is called Indirect Evaporative cooling. Because no moisture is added, the air reaches a lower dry bulb and wet bulb temperature than the outside air when leaving the heat exchanger.
The second stage, that is the adiabatic evaporative cooling, cellulose cooling pad is used which cools the air further through the wet evaporative media. As a result of this two-step cooling process, the air can be brought down to a much lower temperature and is therefore not capable of containing high amounts of humidity.