Indirect evaporative cooling works on the same principle as direct evaporative cooling lowering air temperature by causing water to evaporate. The main difference with an indirect system is that a heat exchanger is used to cool the air supplied to the living space. The evaporative cooling cycle occurs in the heat exchanger.
Here's a sequential explanation of what happens in an indirect evaporative cooling system:
Indirect evaporative cooling provides cool air to interior spaces without as much humidity as direct evaporative cooling. This, cooling method is more suitable for areas where additional humidity isn't desirable for interior air. Because indirect evaporative cooling requires two fans rather than one, it consumes more electricity than direct evaporative cooling.