Simplified Methods for Determining Ventilation Rates in Naturally Ventilated Dairy Barns

摘要

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 11m 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 (Cv) ranging from 0.33 to 0.87. However, after accounting for the effectof wind direction, the mean windward Cv was 0.74+0.29, the mean parallel Cv was 0.54±0.20, and the mean leeward Cv was 0.40±0.20. These Cv-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 COi-baiance method. The latter approach is thus more cost-effective compared to perimeter sampling that requires significantly more gas analyzers.