Which cooling method is most affected by high ambient humidity?

• A. Shading
• B. Fogging
• C. Evaporative pad-and-fan cooling
• D. Forced-air ventilation

Answer: (C)

This method relies on evaporative cooling—the air is cooled as water evaporates from the wet pads into the moving air. The rate of that evaporation depends on the vapor pressure difference between the water and the surrounding air. When ambient humidity is high, the air is already near saturation, so little moisture can evaporate, and the cooling effect drops sharply. That makes evaporative pad-and-fan systems the most sensitive to high humidity.

Shading simply blocks some solar radiation, so humidity doesn’t directly limit its ability to reduce heat input. Forced-air ventilation reduces heat by exchanging air, and while humidity can affect comfort, the cooling mechanism isn’t driven by evaporation and is less impacted. Fogging adds moisture and cools via evaporation too, but its performance is more constrained by ambient humidity than the large-area evaporation in pad-and-fan systems.