A comparative study among H2O-balance, heat balance, CO2-balance and radioactive tracer gas technique for airflow rates measurement in naturally ventilated dairy barns

Abstract

The major problem of natural ventilation is the lack of accurate measurement methods for air exchange rates (AER) which is crucial for emissions quantification. This paper aims at comparing four methods and to recommend thereof one method for further developments. Thirty six experiments were performed to study the AERs in a naturally ventilated dairy barn through four summer seasons and three winter seasons. AERs were determined using moisture (H2O) balance, heat balance (HB), CO2-balance and radioactive tracer gas technique (TGT). The statistical analyses were correlation analysis, regression model, ANOVA and t-test. Continuous measurements of CO2 concentrations, temperature and relative humidity inside and outside the barn were performed. H2O-balance showed reliable results through winter and slightly acceptable results through summer. HB showed slightly acceptable results through summer and unsatisfactory results through winter. CO2-balance showed unexpected high differences to the other methods in some cases. TGT showed reliable results compared to all methods and is independent on physiological parameters. Therefore, TGT should be further developed. The airflow rates (AFRs), subject to TGT, were 0.12 m3 s-1 m-2, 1.15 m3 s-1 cow-1, 0.88 m3 s-1 LU-1 (LU is livestock unit of 500 kg), 395 m3 s-1 and 470 kg air s-1 through summer, and 0.08 m3 s-1 m-2, 0.83 m3 s-1 cow-1, 0.64 m3 s-1 LU-1, 275 m3 s-1 and 328 kg air s-1 through winter. AERs were 37, 81, 63 and 62 h-1 through summer, and 40, 143, 61 and 39 h-1 through winter subject to H2O-balance, HB, CO2-balance and TGT, respectively.