Modeling airborne virus concentrations in filtered swine barns with negative-pressure ventilating systems

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically significant pathogen in the swine industry that can spread through the air. Many swine gestation and farrowing barns with negative-pressure ventilating systems are filtering inlet air to manage airborne PRRSV transmission using MERV 8 pre-filters with either MERV 14 or MERV 16 filters. Recent research reported air infiltration rates for a new 3,000 sow gestation/farrowing swine barn at several static pressure levels. The barn infiltration data and supplier provided filter data were used to model virus particle concentrations inside a well-mixed barn. Other model inputs included the target ventilating rate, fan performance, filter area, filter performance (i.e. pressure drop characteristics and collection efficiency of three particle size ranges), and infiltration rates. For the conditions used, model results indicated that higher barn virus concentrations were obtained with lower mechanical ventilating rates and higher infiltration rates. Improved fan performance reduced the number of fans needed but had little impact on barn virus concentrations. Increasing filter area reduced the pressure drop that the fans had to overcome at higher ventilating rates and correspondingly reduced unfiltered infiltration rates and barn virus concentrations. Model results indicated that when the filter pressure drop/flow rate relation for filters produced higher barn static pressures the infiltration rates and barn virus concentrations increased too. More work is needed to assess the model results and the importance of the factors adjusted for other barn and equipment conditions.