Simulation of air quality and cost to ventilate swine farrowing facilities in winter

Abstract

We developed a simulation model to study the effect of ventilation airflow rate with and without filtered recirculation on airborne contaminant concentrations (dust, NH₃, CO, and CO₂) for swine farrowing facilities. Energy and mass balance equations were used to simulate the indoor air quality and operational cost for a variety of ventilation conditions over a 3-month winter period, using time-varied outdoor temperature. The sensitivity of input and output parameters on indoor air quality and operational cost were evaluated. Significant factors affecting model output included mean winter temperature, generation rate of contaminants, pit-air-exchange ratio, and recirculation ratio. As mean outdoor temperature was decreased from -2.5 °C to -12.5 °C, total operational costs were increased from $872 to $1304. Dust generation rate affected dust concentrations linearly. When dust generation rates changed -50% and +100% from baseline, indoor dust concentrations were changed -50% and +100%, respectively. The selection of a pit-air-exchange ratio was found critical to NH₃ concentration, but has little impact on other contaminants or cost. As the pit-air-exchange ratio was increased from 0.1 to 0.3, the NH₃ concentration was increased by a factor of 1.5. The recirculation ratio affected both IAQ factors and total operational cost. As the recirculation ratio decreased to 0, inhalable and respirable dust concentrations, humidity, NH₃ and CO₂ concentrations decreased and total operational cost ($2216) was 104% more than with pit-fan-only ventilation ($1088). When the recirculation ratio was 1, the total operational cost was increased by $573 (53%) compared to pit-fan-only. Simulation provides a useful tool for examining the costs and benefits to installing common ventilation technology to CAFO and, ultimately, making sound management decisions.

Keywords: Air quality; Ammonia; Dust; Simulation; Simulink; Swine farrowing facility.

Fig. 1

Schematic diagram of the modeled swine farrowing facility, identifying (a) airflow pathways and (b) dimensions. Time-dependent dust generation depicted in panel (c).

Fig. 2

CO, CO₂ concentrations and total operational costs for seasonal mean outdoor temperatures.

Fig. 3

Dust concentrations for filtration efficiency and fraction of dust generation.

Fig. 4

Depiction of sensitivity between inputs and outputs.