Ventilation rate measurements at a mechanically-ventilated pig finishing quad barn

With concentrated animal feeding operations (CAFOs) becoming larger and more intensive, air pollutant emissions from these facilities are of increasing concern for regulators and the public, and on-farm measurements of emissions are needed. A critical step in determining air pollutant emissions from the barns at these facilities is the accurate assessment and continuous monitoring of the barn ventilation rates. One of the most recent efforts to accurately determine barn ventilation rate was to continuously monitor fan operation, differential static pressure, fan speed, and air density related environmental variables, coupled with in-situ fan performance assessments at a range of static pressures, as applied in the 24-month National Air Emissions Monitoring Study (NAEMS). Uncertainty analyses associated with these calculations aided in characterising and qualifying the measurements. This paper describes methods used in the NAEMS to determine ventilation rates of four rooms (rooms 5-8) in a mechanically-ventilated pig finishing quad barn. The overall 2-yr average daily dry-standard ventilation rates (mean ± SD) were 13.5 ± 11.3, 13.8 ± 11.6, 14.5 ± 12.9, and 13.6 ± 12.9 m3 [dry-standard] s−1 for rooms 5-8, respectively. Thorough uncertainty analyses demonstrated that the estimated uncertainty of the ventilation rate (dry-standard) under typical site conditions decreased from 9.4% to 4.1% between the minimum (3.7 m3 [ds] s−1) and maximum (45.2 m3 [ds] s−1) capacities of the ventilation system. These results confirmed that larger numbers of operating fans lead to lower relative uncertainties for barn ventilation rates and that the uncertainty of ventilation rate measurements can be reduced by improved and more frequent in-situ fan calibrations.