Quantifying ventilation effectiveness for air quality control

The term ventilation effectiveness has been widely used to evaluate ventilation systems for air quality control. The application of the term is often either qualitative, rather than quantitative, or difficult for field application. This paper presents the results of quantification of ventilation effectiveness for specific ventilation systems by using a ventilation effectiveness factor (VEF) and a ventilation effectiveness map (VEM). The VEF and VEM are defined mathematically so they can be used to quantify the ventilation effectiveness of a ventilation system. The application of the VEF and VEM was illustrated using a full-scale room case study, which involves comparison of two different ventilation systems: one had a slot air outlet at the opposite wall to the air inlet (Case A), and the other had a air outlet at the same wall as the air inlet (Case B). It is commonly assumed that the locations of air outlets or exhaust fans have little effect on the ventilation effectiveness for livestock buildings. The case studies show that the outlet location had a substantial effect on the ventilation effectiveness for the room airspace as a whole and for specific locations in the room. The differences in ventilation effectiveness for these two systems were quantified in terms of VEF. Ventilation in Case B is three times as effective at dust removal as in Case A. Ventilation effectiveness factors at specific locations within the airspace were also plotted on a VEM. One of advantages of VEF is that a ventilation system can be its own control for comparison of ventilation effectiveness, instead of requiring a control and a treatment. This feature is particularly useful in system evaluation or troubleshooting because it is often very difficult and expensive to have an identical system to compare.