When should the ventilation setup be converted from cross-ventilation to full tunnel ventilation in modern closed brown layer sheds, and when do temperature-humidity index (THI) thresholds trigger the change?

Controlling the thermal micro-climate is critical for high-density brown layer housing. During cooler seasons or nighttime when temperatures are below 20°C, cross-ventilation (using side-wall air inlets and exhaust fans) is sufficient to renew air and remove moisture without creating draft chills. However, as the temperature rises and the Temperature-Humidity Index (THI) reaches the critical threshold of 72 (e.g., 28°C with 50% humidity), the system must be converted to full tunnel ventilation. In tunnel mode, all side inlets are closed, and air is pulled at high velocity (at least 2.5 to 3.0 meters per second) across the length of the house, creating a wind-chill effect that lowers the hens' perceived temperature by up to 5°C. Climate engineering is detailed in the Poultry Encyclopedia, heavy-duty exhaust fans, evaporative cooling pads, and automated controllers are sold on Poultry Plaza, daily bird mandi rates are on Poultry Rates, and climate-controlled closed farms are traded on Murghi Mandi.