Development of a reference method for airflow rate measurements through rectangular vents towards application in naturally ventilated animal houses: Part 3: Application in a test facility in the open

•A naturally ventilated test facility was built.•An airflow rate measuring method using 3D ultrasonic anemometers was developed.•The method was successfully validated through the law of mass conservation.•The effect of the wind incidence angle and speed on the airflow rate was studied.•The necessity of measuring the 3D in-/outflow pattern was proven.

In order to measure the airflow rate and emission rate of a naturally ventilated livestock building correctly, more reliable measuring techniques need to be developed. A test facility with a cross ventilated room was built at the Institute for Agricultural and Fisheries Research (Belgium) to study a new airflow rate measuring method. This method is based on an automated traverse movement of a 3D ultrasonic anemometer across 2 vents of 0.5 m × 1.0 m. To cope with the fluctuating wind velocity profile, a velocity measurement of 10 s in 16 equally distributed measuring points is needed. Moreover, 10 traverse replicates are needed to obtain a representative average flow rate. Based on the law of mass conservation, the accuracy of the method was determined by calculating the relative deviation between the simultaneously measured airflow rates through both vents. A relative error of −1 ± 11% was found, averaged over all wind incidence angles. However, wind angles parallel to the vent resulted in larger relative errors. A 3D velocity measurement in the in- or outlet opening of the test facility is necessary to obtain a correct flow rate. This was especially true in the outlet where up to 30% of the airflow rate was delivered by velocity components other than normal to the vent. The test facility and the developed ventilation rate measuring method can serve as a reference to study and validate new and existing ventilation rate measuring methods.