Developing the 85Kr tracer gas technique for air exchange rate measurements in naturally ventilated animal buildings

Experiments were performed to study air exchange rates (AER) occurring in naturally ventilated dairy buildings during summer seasons 2006 to 2010. A tracer gas technique (TG) for AER measurements was developed. The AERs were determined by decay of radioactive tracer Krypton-85, and CO2-balance used as the reference method (RM). During each experiment, continuous measurements of gaseous concentrations (NH3, CO2, CH4 and N2O) inside and outside the building and 85Kr tracer gas experiments were performed. The combined factors investigated were release over feeding table (a1) or over the manure alley (a2), average α-values (b1) or the sum of impulses (b2), selected radiation counts (c1) or all radiation counts (c2). The results were compared using Pearson correlation analysis, developing a linear regression model, and testing the differences between the factor combinations and the RM using an ANOVA model. There were differences between impulses (Pr > |t| = 0.0013), where the sum of impulses showed better results than the average α-values. Although there was no difference (Pr > |t| = 0.344) between the readings of the radiation counts, it was considered that by using all the readings of the radiation counters it was more representative and easier to calculate the AER. The best factor combinations, having the highest coefficient of determination values R2, and the most reliable parameter estimates, were: a1b2c2 (R2 = 0.94; 1.63 ± 0.14); and a1b1c1 (R2 = 0.97; 2.03 ± 0.11). The gaseous emissions, subject to the RM, were 3.9, 19, 1656, and 0.96 g h−1 AU−1 (AU is animal unit of 500 kg) for NH3, CH4, CO2 and N2O respectively.