Development of a reference method for airflow rate measurements through rectangular vents towards application in naturally ventilated animal houses: Part 1: Manual 2D approach

• An airflow measuring method using 2D ultrasonic anemometers was developed.
• The accuracy of this method was investigated for different airflow rates.
• The influence of turbulence intensity and edge effects on this method was examined.
• Steps towards the use of such a method in naturally ventilated openings were made.

Currently, there exists no reliable method that can produce a detailed image of the velocity profile in a naturally ventilated (NV) opening of a livestock building. The challenge in measuring the velocity profile and in extension the airflow rate, lies in the stochastic variability of the velocity profile in a vent of a NV building. Therefore, the objective of this study was the development of a method that can accurately measure a wide variety of velocity profiles. This is a primary step in the development of a robust reference measurement method for airflow rates and emissions from NV stables. As there is no reference for naturally induced airflows available, the accuracy of the method was estimated by comparison to a reference technique for mechanical ventilation (VDI 2041). A deviation from this reference of max. 10% was deemed acceptable. A measurement method for the airflow rate through the rectangular outlet section of a duct of 0.50 m × 1.00 m was developed with the use of 2D ultrasonic anemometers. For 8 different airflow rates ranging from 1040 m3/h to 6215 m3/h the method’s deviation from the reference remained under the 10% limit with a maximum of +6.3%. Experiments indicated that the method was able to handle flow disturbances, induced close (0.50 m) upstream the measuring plane, with a limited increase in deviation. The results from this research are a stepping stone towards the measurement of more complex velocity profiles and the implementation of such a method in NV systems.