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11Currently there exists no generally accepted reference technique to measure the ventilation rate 12 through naturally ventilated (NV) vents. This has an impact on the reliability of airflow rate control 13 techniques and emission rate measurements in NV animal houses. As an attempt to address this issue a 14 NV test facility was built to develop new airflow rate measurement techniques for both side wall and 15 ridge vents. Three set-ups were used that differed in vent configuration, i.e. one cross ventilated set-up 16 and two ridge ventilated set-ups with different vent sizes. 17The airflow through the side vents was measured with a technique based on an automatic traverse 18 movement of a 3D ultrasonic anemometer. In the ridge, 7 static 2D ultrasonic anemometers were 19 installed. The methods were validated by applying the air mass conservation principle, i.e. the inflow 20 rates must equal the outflow rates. 21The calculated in-and outflow rates agreed within (5 ± 8)%, (8 ± 5)% and (-9 ± 7)% for the three 22 different set-ups respectively, over a large range of wind incidence angles. It was found that the side 23 vent configuration was of large importance for the distribution of the airflow rates through the vents. 24The ridge proved to be a constant outlet, whilst side vents could change from outlet to inlet depending 25 on the wind incidence angle. The range of wind incidence angles in which this transition occurred 26 could be clearly visualised.

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