Site, environmental, and airflow characteristics for mono-slope beef cattle facilities in the northern great plains

In conjunction with an emission monitoring study, long-term airflow and environmental data were collected from select pens in each of four regional producer owned and operated mono-slope beef cattle facilities in the Northern Great Plains. The barns were oriented east-west, with approximate depths of 30 m in the north-south dimension, 82 to 333 m widths in the east-west dimension, and south and north wall eave heights of 8 and 5 m, respectively. The north wall curtain openings were adjusted by the producers seasonally or daily, and classified as open (>1.5 m, mean SD = 2.1 m 0.1 m) or closed (<1.5 m, mean SD = 0.6 m 0.2 m). The temperature, relative humidity, and air velocity through the north and south wall openings were monitored at a fixed height near the center of the openings. On-site weather towers provided corresponding ambient temperature, relative humidity, and air velocity and direction data. The airflow was calculated as the product of the air velocity and opening area. The hourly mean airflows for the north and south wall openings were modeled as functions of perpendicular (to the barn opening) ambient air velocity (10 m height) and curtain opening. Theoretical airflows using the wind pressure coefficient method were also calculated. Based on comparisons between monitoring locations within an opening, north and south wall opening airflows, and measured versus theoretical values, greater confidence was given to airflow measurements for southerly airflow and open conditions. Airflow measurements for northerly flow and closed conditions were low compared to theoretical values. The uncertainties associated with the monitoring method are discussed, and the north wall opening airflow was deemed a reasonable measurement of airflow through the barn (i.e., for emission calculation purposes) for open and closed conditions. With a 5 m s-1 south wind, there were approximately 10 to 70 air changes per hour (ACH) for closed conditions in the four barns, and 160 ACH with open curtains. The average relationships between airflow through the pen volume and ambient wind velocity were 7 and 33 ACH (m s-1)-1 for closed and open conditions, respectively. These data assist producers in management decisions, and are required for aerial pollutant estimation for this type of beef cattle facility in the Northern Great Plains.