Answer Happy

A B Figure 1 Two units (Unit A and Unit B) at different floors with single-sided windows
Assuming a multistory building contains two up-down units (i.e. these two units located adjacently at different floors) with single-sided windows in both units, as shown in Figure 1, the two units are identical (in terms of dimension and volume). (1) Please explain the tracer gas decay method used to measure the ventilation rate of Unit B. (2) If Unit B is settled with a tracer gas source in the middle of the unit, then after a certain time (when a steady-state airflow and mixing process and well-mixed conditions for both room units are reached), the concentration of the tracer gas in Unit A is 0.106 g/m³, the concentration of the tracer gas in Unit B is 1.35 g/m³. The ACH air change rate (per hour) of Unit A is 6.95 times/hr and the ACH air change rate (per hour) of Unit B is 6.37 times/hr. Calculate the re-entry ratio R of the tracer gas from Unit B to Unit A. Given: By assuming a steady-state airflow and mixing process and well-mixed conditions for two adjacent room units, the re-entry ratio R of the tracer gas is calculated by Rk = Mi-j' Volj(ACH)j Voli (ACH)i where Mi-j is the mass fraction and is defined as the pollutant (or the monitored tracer gas) concentration of air that originates from the source unit i and is present in another unit j, Vol; and Vol; are the room volumes of the source unit i and the receiver unit j respectively, and (ACH); and (ACH), are the air change rate per hour of the source unit i and the receiver unit j respectively. =