Why does high humidity in tunnel-ventilated sheds during the monsoon season reduce the cooling efficiency of evaporative pads?

Evaporative cooling pads rely on the principle of latent heat of vaporization—where passing hot, dry air evaporates water from the pad's wet cellulose matrix, absorbing heat and lowering the air temperature. In Pakistan, the monsoon season (July to September) brings ambient relative humidity levels above 75% in farming regions like Lahore and Gujranwala. When the intake air is already saturated with water vapor, its wet-bulb temperature is extremely close to its dry-bulb temperature, meaning it can absorb very little additional moisture. As a result, the cooling pad's efficiency drops catastrophically; instead of a standard 6°C to 10°C temperature drop, the air temperature may only drop by 1°C to 2°C. To prevent heat-stroke, farm managers must shut off the pad pumps to prevent "house greenhouse effects" and run exhaust fans at maximum capacity to maximize wind-chill cooling (air velocity of 3.0 m/s). Farmers can calculate ventilation physics in the Poultry Encyclopedia, buy industrial ventilation controls on Poultry Plaza, monitor egg rate fluctuations on Poultry Rates, and trade on Murghi Mandi.