The precise determination of Greenhouse gas (GHG) emission is a paramount topic in nowadays research and society. In the case of naturally ventilated dairy barns, on-farm measurements are always accompanied with high uncertainties caused by dynamic weather conditions, animal activities, and the diversity of the barns’ dimensions and geometries. This poses an emerging challenge to mitigate emissions since mitigation measures can only be effective with in-depth knowledge about the gas emission process, ventilation performance, and the airflow patterns. We deployed computational fluid dynamics (CFD) models to investigate the relationship between incoming wind angle and the air exchange rate (AER) of a typical symmetrical dairy barn under three types of convection flow regime. In parallel, the flow pattern at three different heights were compared using the image analysis metric mean square error (MSE). We discovered that for natural convection the AER deviation is around 18% on average for different wind angles. For mixed and force convection, the AER deviation was below 30% for wind angles until 60°. Also, a critical wind angle round 63° was found, from which the wind angle strongly influenced the AER deviation as the forced convection became stronger. The analysis of the MSE values for the considered cases at the three heights showed similar variations in the airflow pattern. In conclusion, considering a wind corridor of up to +/- 60° relative to the crossflow can be considered reasonable for on-farm air exchange rate measurements.
Chen et al. (Thu,) studied this question.