Air velocity measurements using ultrasonic anemometers in the animal zone of a naturally ventilated dairy barn

Air velocity measurements were collected from one horizontal plane across the entire animal occupied zone (AOZ) floor area of a dairy barn. Data recorded from the undisturbed approaching airflow (25° deviation from normal to the sidewall of the building) and an approach flow disturbed by obstacles (surrounding buildings) in front of the barn (at an incident angle of 20° from normal to the building facade) were analysed. The 96.2 m long, 34.2 m wide and 10.7 m high (ridge) building had open sidewalls, wind protecting nets and large openings in both gable walls. The barn, with a loose housing system with freestalls, accommodated 364 dairy cows. The outside temperatures were between 10 and 20 °C, and the outside wind speeds were between 0.7 and 3.9 m s−1. The air speed in the AOZ varied from 0.2 to 1.4 m s−1. Differences between single areas inside the barn were large and led to different climatic conditions for different animal groups. The undisturbed approaching airflow (at an incident angle of 25° from normal) resulted in a heterogeneous airflow pattern inside the barn with no defined outlet. This airflow pattern was probably influenced by the surrounding buildings on the leeward. In contrast, the disturbed approaching airflow (with obstacles at the windward side) resulted in a homogeneous flow pattern with a lower airflow. A linear model showed that only the interaction between the outside wind speed and the outside wind direction significantly influenced the inside air velocity. Long term measurements at or above the AOZ are needed to complement existing data.