Analysing ventilation efficiency in a test chamber using age-of-air concept and CFD technology

The age-of-air concept can be used to assess the ventilation efficiency of an agricultural facility. However, experimental research has been limited due to the indirect method of using unstable tracer-gas and limited instrument. To overcome limitations and increase applicability, CFD technique was employed from established methodology by user-defined functions. A three-dimensional chamber was designed to accurately implement and verify the age-of-air through simulation and tracer-gas experiment under unsteady-state conditions. In validating the computations of the local-mean-age and local-mean-residual-lifetime, the results showed similar quantitative and qualitative distributions with average errors of 9 and 13%, respectively. It could be concluded that the method of realising the age-of-air via CFD was reasonably well designed and capable of estimating ventilation efficiency of agricultural facilities under unsteady-state conditions. The results also showed that when air exchange rate (AER) increased in the target structure, the age-of-air values decreased, but when comparing air exchange efficiencies, the values had an opposite tendency. Through the methodology presented in this study, the feasibility of analysing ventilation efficiency using Age-of-air in agricultural facilities was confirmed and it will be upgraded for actual application considering characteristics of ventilation structure. Through the methodology presented in this study, the feasibility of analysing ventilation efficiency using age-of-air in agricultural facilities was confirmed and it will be upgraded for actual application considering characteristics of ventilation structure. ► Method for analysing and understanding ventilation efficiencies using CFD. ► Based on age-of-air concept in unsteady-state to address agricultural ventilation. ► 3D chamber designed as preliminary to working with the real agricultural structure. ► Methodology to realise age-of-air established via user-defined-function. ► Tracer gas experiment conducted for validation.