WINTER MEASUREMENTS OF AIR EXCHANGE RATES USING TRACER GAS TECHNIQUE AND QUANTIFICATION OF GASEOUS EMISSIONS FROM A NATURALLY VENTILATED DAIRY BARN

Measuring the ventilation rates and then quantifying the gaseous emissions from naturally ventilated barns is a particularly difficult task and associated with large uncertainties; where no accurate, reliable, and online method is available for ventilation rate measurements. Therefore, the objective of this study was to develop further the tracer gas technique (TG) for ventilation rate measurements through winter seasons. Fifteen field experiments were carried out to study the ventilation rates in a naturally ventilated dairy barn located in North Germany through three consecutive winter seasons. During each field experiment, continuous measurements of gaseous concentrations (NH3, CO2, CH4, and N2O) inside and outside the barn and tracer gas experiments were carried out. Meanwhile, the microclimatic and climatic conditions were measured and recorded. The air exchange rates (AERs) and then the ventilation rates were estimated by the TG and the CO2-balance which was set as reference method, in this study, for the purpose of statistical analysis. Three factors with two levels each were tested and they are: Kr-85 point release source versus Kr-85 line release source, average a-values versus sum impulses, selected radiation counters versus all radiation counters; resulting in eight factor combinations. The results were compared with each other by developing a linear regression model and carrying out Pearson correlation analysis. The differences between the reference method and the eight factor combinations were tested using the ANOVA model. The results showed that the best factor combinations were: (1) line release source considering the impulses recorded by selected radiation counters and implementing the sum method of all impulses where high R-square value of 0.82 and reliable parameter estimate of 1.00 +/- 0.19 were found for this combination, and (2) point release source considering the impulses recorded by all radiation counters and implementing the sum method of all impulses where high R-square value of 0.91 and reliable parameter estimate of 1.19 +/- 0.15 were found for this combination. The average gaseous emissions through the different winter seasons, subject to the reference method, were 2.9, 14.5, 1785, and 1.6 g h(-1) AU(-1) for NH3, CH4, CO2, and N2O, respectively.