ASABE Technical Library - Abstract

Abstract. This research investigated two simple direct methods and one simple indirect method for measuring air exchange rate (AER) in naturally ventilated (NV) dairy barns. The first direct method was based on measurement of wind speed at a local weather tower (WT) installed 11 m high. The second direct method involved measurements of airflow speed at only one location in the barn, while the third method (indirect) comprised indoor-outdoor CO₂ concentration measurements. The correlations of determination between actual airflow velocities at respective barn openings and the corresponding wind velocities at the WT were statistically strong (R² = 0.46 to 0.91), with ventilation coefficients () ranging from 0.33 to 0.87. However, after accounting for the effect of wind direction, the mean windward was 0.74±0.29, the mean parallel was 0.54±0.20, and the mean leeward was 0.40±0.20. These -values were used to calculate average airflow rate for each sidewall for different wind directions. The estimated barn AER by the simple method correlated well with reference barn AER (r = 0.78). Barn AER was also determined accurately with one-velocity measurement near the center of the barn using correction factors ranging between 2.3 and 2.6. Results also indicated no significant differences between perimeter sampling regime and indoor-outdoor sampling regime when determining barn AER using the CO₂-balance method. The latter approach is thus more cost-effective compared to perimeter sampling that requires significantly more gas analyzers.