A Two Stage Evaporative Cooler is also called as an indirect cooling system which uses the latest evaporative cooling system technology. This system is more energy efficient than air conditioning systems.
Two-stage evaporative refers to the stages of cooling that happens in the process. In the first stage the air passes through a heat exchanger where the air is cooled, during this initial phase the air does not pick up any moisture. In the second stage, the same air passes through a dampened pad where the additional cooling takes place and the air picks up some additional humidity.
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. That's why it is called Indirect Evaporative cooling. Dual-stage combined is also called the Indirect Direct Evaporative Cooling system. It additionally uses a heat exchanger called DAMA.
In Two-stage Evaporative cooling, no free moisture is added to the incoming air and because of this fact it is sometimes called dry evaporative cooling. Two-stage Evaporative coolers are also known as Indirect Direct Evaporative Cooler.
Two-stage evaporative cooling system use a pre-cooler, more efficient pads, and more efficient motors, and do not add a lot of moisture to the room as compared to single-stage evaporative coolers. As they are expensive as compared to the single stage coolers they are used in areas where the day temperature exceeds 100°F.