Evaluation of the effects of contaminant injection location and injection method on the determination of overall relative room ventilation efficiency

Abstract

The purpose of this research is to evaluate an emerging concept called ventilation effectiveness at several points in a real room. Ventilation effectiveness was calculated using the pulse and step-up injection methods which were performed in four different locations in a room. Using the pulse method of injection, the calculated average ventilation effectiveness changed as the injection point location was changed. However, statistically different ventilation effectiveness factors were only found between the typical and stagnant injection locations. Two major problems were found while calculating ventilation effectiveness for the step-up injection method. The first problem was the estimation of steady state concentration. The second problem was that the equation for ventilation effectiveness has a singularity when it is evaluated over a finite measurement time. The first problem was solved using control chart techniques for running averages. The second problem was analyzed further using an exponential function characterizing a perfectly mixed room. The analysis revealed that the ventilation effectiveness equation is not defined for all values of the ratio of the true steady state concentration to the assumed steady state concentration, Ctme SS/C assumed Ss, and finite integration times. Fitting an equation to the concentration data and extrapolating to infinity is one method to avoid the discontinuity, but the quality of fit of the function to the data depends on the amount of scatter in the data. In conclusion the pulse injection method is better than the step-up injection method because ventilation effectiveness is defined for all integration times and has less uncertainty.