Development of a direct measuring method for determining airflow rates in naturally ventilated dairy barns with ventilation screens

Emission measurements to supply accurate, representative emission numbers to legislators and other stakeholders remain a challenge to this day in naturally ventilated dairy barns. This study aims to demonstrate a method for measuring airflow rates in naturally ventilated dairy barns with operational ventilation screens with the aim of determining emissions in a fully operational dairy barn. This method employs vertical sensor profiles of ultrasonic anemometers (UAs) for measuring incoming and outgoing airflow rates using a trapezoidal integration approach for (partly) open ventilation screens, while for closed screens, a partial areas approach in the ridge opening is used. Air velocity patterns were investigated at different ventilation screen heights, which resulted in different adjustments in flow channel height between incoming and outgoing airflow. This approach resulted in a direct method applicable in a wider range of measurement conditions, and in a balance between incoming and outgoing airflow rates closer to equivalence compared to the current state-of-the-art employing partial areas with centrally positioned UAs. This resulted in average relative differences of −5 % and 11 % between incoming and outgoing airflow rates, compared to between 26 and 36 % for the state-of the art. However, non-unidirectionality in the sidewall openings due to near-parallel wind incidence angles resulted in a significant loss of data (37.8 %), which potentially increases the uncertainty emission numbers derived with this method.