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Negative Pressure Ventilation vs Evaporative Cooling

Negative pressure ventilation and evaporative cooling are often sold as alternatives, but they are different layers of the same system. Negative pressure is an air movement method: it controls where air enters and leaves. Evaporative cooling is an air treatment method: it cools the air that enters by passing it through a wet pad or a wet surface. A pad-and-fan system combines them: negative pressure fans create the pull, and the pad cools the incoming air. A factory with rooftop exhaust alone has negative pressure without evaporative cooling. A mobile evaporative cooler in an open space has evaporative cooling without a controlled negative pressure path. The right question is therefore not which one to choose, but which layer your space is missing: does it need more air exchange, cooler incoming air, or both?

The humidity cost belongs in the same decision. Evaporative cooling adds moisture to the air it delivers. In a hot, dry climate that is a benefit twice over: cooler air and more comfortable humidity. In a hot, humid climate the cooling effect is smaller and the added humidity can become a problem, especially for stored goods, for workers, and for animals already stressed by humidity. In that case the answer may be more air exchange without a pad, or a refrigerant system for a sealed space, rather than a larger evaporative cooler. State the humidity on site in your inquiry, not just the temperature.