Design of Ventilation Systems for Calf Hutches to Mitigate Cold and Heat Stress Using Computational Fluid Dynamics (CFD) Simulations

Environmental conditions in outdoor calf hutches directly affect calf growth, health, and early-life development. Most existing research addresses heat stress mitigation in lactating cows, while heat and cold stress in pre-weaned calf hutches, together with the role of bedding total water content, have received limited attention. In this study, we developed and validated computational fluid dynamics (CFD) models to quantify the effects of photovoltaic (PV)-powered fan ventilation on airflow, hutch temperature, bedding total water content, and cold and heat-stress indices. CFD simulations showed that under cold weather conditions (5.9 ± 0.72 °C), fan operation doubled bedding-layer air velocity and reduced total water content from 30 to 19.6%, from 60 to 43.2%, and from 90 to 74.3%. Under the same conditions, fan operation increased Comprehensive Climate Index (CCI) values at the entrance of the hutches from 5.36 to 5.48 °C at 30% total water content and from 5.16 to 5.32 °C at 60% (p < 0.0001), while no significant change was observed at 90%. During warm conditions (16.07 ± 0.09 °C), fan operation reduced mean temperatures by 1.2–1.4 °C, increased air velocity by up to 78%, reduced total water content to 22.6%, and lowered CCI by 6.8–9.5% (p < 0.001). Under hot conditions (30.37 ± 0.43 °C), fan use reduced average hutch temperature from 33.8 to 30.7 °C, while combining fans and a reflective cover achieved a 3.6 °C reduction (p < 0.0001). CCI decreased from 37.5 to 35.1 °C, and the temperature-humidity index (THI) decreased by up to 7.3 units. PV-powered ventilation improved airflow distribution and reduced heat stress risk in calf hutches. In cold weather, PV fans lowered bedding moisture and hutch humidity, two contributors to cold stress risk, without creating drafts, although keeping the bedding material dry remained essential.