Assessing Air Velocity Distribution in Three Sizes of Commercial Broiler Houses During Tunnel Ventilation
Convective cooling is a critical management strategy for maintaining an environment that promotes production efficiency, thermal comfort, and animal well-being in commercial broiler houses. Variations in house size, design, and equipment configuration contribute greatly to the air velocity distribution within the facility. This study assessed total airflow, air velocity distribution, and quantified the floor area in three facilities experiencing insufficient air velocity for maintenance of production efficiency, thermal comfort, and animal well-being. Test facility 1 was an 18.3 x 170.7 m solid side-wall broiler house, test facility 2 was a 15.24 x 144.8 m solid side-wall broiler house, and test facility 3 was a 12.19 x 121.9 m curtain side-wall broiler house. Total airflow of each facility, measured with a Fan Assessment and Numeration System, was 512,730, 389,495, and 329,270 m3 h-1 for test facilities 1, 2, and 3, respectively. Air velocity distribution patterns were characterized in each house with a Scalable Environment Assessment System (SEAS) and spatial statistics. The air velocity distributions within the test facilities were variable, with notable maxima immediately downstream of the tunnel inlets, which serve as a well-defined vena contracta, and local minima near the leading end of the evaporative pads and the exhaust fans. Equipment within the facilities had an impact on the air velocity distribution by creating reduced cross-sectional areas that resulted in localized increases in air velocity. The percentage of total bird-level floor area in each facility experiencing air velocities below 1.5 m s-1 was 14.3%, 20.7%, and 10.0% for test facilities 1, 2, and 3, respectively. The effective design velocity (Ved) was calculated from total airflow using the measured building cross-sectional area. The Ved measured 2.97, 2.45, and 2.34 m s-1 for test facilities 1, 2, and 3, respectively. Mean cross-sectional air velocity (Vcs) was calculated from SEAS data and normalized using each facility‘s Ved to account for differences in building size for comparison. Test facility 1, the largest of the three houses, generated substantially higher Vcs/Ved than test facilities 2 and 3. Test facilities 2 and 3 maintained a larger proportion of Vcs above Ved than test facility 1. Test facility 1 showed 26.5% of the total house length below Ved, while test facilities 2 and 3 had only 20.8% and 17.5%, respectively, of the total house length below Ved. The lower-velocity regions were due to the length of the evaporative cooling pad inlet and the use of tunnel doors, and the exhaust fan placement on the side-walls in test facility 1 created an additional pronounced low-velocity area. Placement of tunnel ventilation fans on the end-wall of the facility, rather than the side-wall, eliminated the low-velocity region at the exhaust end of the facility. Modifications to current practices for broiler production facility construction and evaporative cooling pad inlet installation would be required to minimize the low-velocity region at the inlet end of these facilities. Consideration of house width and physical arrangement of the air inlets, tunnel fans, and internal equipment are critical for improving the uniformity of air velocity in commercial broiler houses.