Indirect Evaporative Cooling

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:

1. Hot outside air is blown through a heat exchanger that is supplied with water. One design for this type of heat exchanger features a series of metal tubes that are kept wet on their outside surfaces. As hot air passes over these tubes, the water evaporates and the tubes are cooled. After passing over the tubes, the cool, moist air is exhausted to the outside.
2. As cooling happens on the heat exchanger's exterior surfaces, hot exterior air is drawn through the tube interiors. This air is cooled, but without gaining any extra humidity, before it is blown through ductwork to the building interior.

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.