Comparison of different mechanical ventilation systems for dairy cow barns: CFD simulations and field measurements

Abstract

Proper ventilation in dairy cow barns in terms of volume flow rate and air velocity is important to avoid heat stress, which leads to reduced milk production and respiratory disease. In this study, three different ventilation systems for dairy cow barns were compared in terms of the airflow inside the barn using Computational Fluid Dynamics (CFD) simulations. The 3D steady simulations were validated against velocity point measurements in a dairy cow barn, with the average difference being within 15%. The first system (barn A) had four inlet fans, 36 sidewall inlet fans, and eight exhaust fans. The second system (barn B) had no inlet fans and ten exhaust fans. The third system (barn C) had six inlet fans and eight exhaust fans. In all three barns, circulation fans were located above the cows resting areas. The results showed that the percentage of the barn's total volume flow rate through the resting area in barn C was 50% and 10% higher than barns A and B, respectively. High air velocities between 3 and 5 m/s was obtained in barn C, the same was only obtained in half of barn B near the exhaust end, while barn A showed the lowest performance. It was shown that it is necessary to have fans on the inlet and exhaust ends of the barn (barn C) to obtain relatively sufficient and uniform air velocity along the barn. Furthermore, the results showed that inlet end fans and sidewall inlet fans (barn A) worked against each other, leading to low air velocity and volume flow rate through the animal occupied zones; therefore, their combination is not recommended.