Air exchange rate measurements in naturally ventilated dairy buildings using the tracer gas decay method with 85Kr, compared to CO2 mass balance and discharge coefficient methods

Abstract

Emission fluxes from naturally ventilated cattle buildings are usually calculated as the product of gas concentrations and the air exchange rate (AER). One key issue is the measurement of the AER throughout such buildings. The aim of this study was to investigate three different methods for AER estimation in naturally ventilated dairy buildings: (1) the concentration decay of the tracer gas Krypton 85 using two different evaluation procedures, (1a) sum 85 Kr, in which the impulses from all the single 85 Kr sensors are combined into one cumulative curve and (1b) ave 85 Kr, which averages the AERs obtained from single 85 Kr sensors; (2) the carbon dioxide mass balance model (CO 2 M); and (3) the discharge coefficient method (DCM). These three methods were compared with each other using both our own measurements and results from the literature. The comparison was statistically evaluated using analysis of variance (ANOVA). The effects of the external conditions of wind velocity and temperature and the effect of nearby buildings on the differences between the methods were predicted. The concentration decay of 85 Kr and the DCM generally produced higher AER values than the CO 2 M (mean ± standard error (SE), 22.8 ± 7.2 h −1 ). These differences were determined to be 8.5 ± 3.1 h −1 ( P = 0.007) for the sum 85 Kr method and 12.9 ± 3.1 h −1 ( P 85 Kr can also be used to estimate higher AER ranges when the difference between the CO 2 concentrations inside and outside the building is below 200 ppmv. The sum 85 Kr method is the recommended procedure for tracer decay analysis for AER estimation.