Age of Air Measurement in Air-recirculating Systems Applying Dynamic Steady-state Concentration Theory

Abstract

In open air systems which is rooms with ventilation by fresh air, the evaluation of an indoor air environment based on age of air measurement, such as a stepdown method using tracer gas, is widely applied. However, in a ventilation room with air-recirculating systems such as multiple packaged air conditioning unit systems, the concentration continues to increase endlessly when there is no ventilation with fresh air. Thus, it is not possible to measure the air age using the conventional experimental method, as noted. Therefore, in previous studies, a tracer gas experiment was established by applying a dynamic steady-state concentration theory. The dynamic steady-state concentration is the concentration transition of each single source, assuming that the steady-state concentration is composed of the difference between the room source and the recirculating source. Previous studies have confirmed that the dynamic steady-state concentration agrees with the equivalent steady-state concentration in the ventilation room of an open air system. In addition, simulations by computational fluid dynamics (CFD) analysis and tracer gas experiments in the laboratory showed that the dynamic steady-state concentration of only the recirculating part of the source equals the age of air. With all these methods and studies, we attempted to extend to a real space with air-recirculating systems using the tracer gas experimental method based on dynamic steady concentration. First, we measured the air age in a real space with multiple packaged air-conditioning unit systems. We thereafter confirmed the distribution property of the multiple packaged air conditioning unit systems and verified the validity of the quantitative evaluation using CFD analysis. Our findings were as follows:

1.The age of the air measurement in a room with two or more recirculating parts was clarified by applying the dynamic steady-state concentration theory. 2.The tracer gas experiment of the dynamic steady-state concentration enabled the quantitative evaluation of the air distribution characteristics of the multiple-packaged air-conditioning unit system in real space.