Wind tunnel study on effect of wind directions on ventilation inside a naturally ventilated pig barn with an outdoor yard

Naturally ventilated pig barns equipped with outdoor exercise yards (NVPBOYs) have the potential to alleviate issues related to poor animal well-being and excessive gaseous emissions compared with conventional intensive pig farming. However, as a novel pig housing system, the information on the ventilation process of NVPBOYs with respect to variable outdoor wind directions remains unclear. Therefore, the objective of this study is to investigate the influence of wind direction on the indoor airflow pattern and ventilation rate of NVPBOYs. The investigations were performed using a 1:50 scale model of an NVPBOY in a large boundary layer wind tunnel. Air velocities inside the scaled model under four wind directions (0 $°$, 60 $°$, 120 $°$, and 180 $°$) were measured using a Laser Doppler Anemometer. The results indicate that: 1) Airflow patterns in the exercise yard are more sensitive to the changes in wind direction compared to those in the indoor room. 2) Oblique wind (60 $°$ and 120 $°$) results in lower ventilation rates, accounting for 50 %–65 % of the ventilation rate observed under perpendicular winds (0 $°$ and 180 $°$). 3)The yard directs the high-speed air stream to the upper part of the barn. The pitched roof and the gable wall of the indoor room lead the fresh air to the animal-occupied zone in the indoor room. The yard and the indoor room thus result in different local environments between them, supporting the intended purpose of the NVPBOYs to separate pigs’ excretion and sleeping areas. The results of this study contribute to a good understanding of the ventilation process of NVPBOYs to achieve a better design and control of their housing and ventilation systems.