Effect of sampling density and location on airflow rate measurements in a naturally ventilated pig barn with an outdoor exercise yard: A boundary layer wind tunnel study

An accurate ventilation rate estimation is the basis for developing ventilation strategies, optimising indoor air quality and determining pollutant emissions from livestock buildings. To accurately quantify the airflow rate of a novel naturally ventilated pig barn with an outdoor exercise yard, the influence of sampling density and location on the airflow rate measurement was studied. The experiment was conducted in a large atmospheric boundary layer wind tunnel by measuring the airflow velocity at the openings (the yard opening and the window of the indoor room) of a scaled pig barn model. Under four wind directions (0 $°$, 60 $°$, 120 $°$, and 180 $°$), the study evaluated four sampling densities distributed separately along the vertical or the lateral directions of the opening, different mesh-like sampling strategies, and airflow rate measurement with or without considering the edge effects of the opening. The results showed that: 1) Sampling densities distributed vertically and laterally along the yard opening, as well as those distributed vertically along the window, were significantly affected by wind directions (p < 0.05). 2) The mesh-like sampling strategy can ensure accurate measurement results with a difference ratio of less than 5 %. 3) Suitable sampling densities without considering the wall effect caused by the vertical edge of the opening can still support reliable airflow rate measurement. The results of this study contribute to developing the direct method of airflow rate measurements in naturally ventilated livestock buildings.