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

In order to measure the airflow rate and emission rate of a naturally ventilated livestock building cor- rectly, 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 0.5m? 1.0 m. To copewith the fluctuatingwind velocity profile, a velocity measurement of 10 s in 16 equally distributed measuring points is needed. Moreover, 10 traverse repli- cates 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 veloc- ity 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 com- ponents 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.