## 3 Results
### Exchange Airflow Rate through the Protecting Door's Clearance Opening  
Figure 15 presents variation in the airflow rates at the protecting door's clearance opening on two representative floors. The elevator car moved from the 1 st floor to the 15 th floor and then was parked on the 15 th floor for 8 s, which corresponds to Case 1. After that, the elevator car moved downward from the 15 th floor to the 1 st floor and was parked on the 1 st floor for another 8 s, which corresponds to Case 2. The position of the elevator car was also plotted on the upper boundary of each subfigure. A positive airflow rate represents the flow from the shaft to the lobbies, while a negative airflow rate for the flow from the lobbies to the shaft. Figure 14: Pollutant distribution at different times when the elevator car moved downward from the 15 th floor to the 1 st floor in Case 2: (**a**) at \(t=33.3\) s, i.e., 0.1 s after the car started to move downward from the 15 th floor; (**b**) at \(t=42.3\) s when the car just reached the 10 th floor; (**c**) at \(t=51.2\) s when the car just reached the 5 th floor; (**d**) at \(t=58.4\) s when the car just reached the 1 st floor. As shown in Figure 15a, when the elevator car moved from the first floor from \(t=0\) to \(t=1.0\) s, the clearance opening on the second floor was above the elevator car, which resulted in positive flow from the shaft to the lobby. Once the car passed the protecting door's opening, the airflow rate was reduced sharply from a positive flow rate to a negative one. The airflow rate swung with time due to the intermittent passing of the door's opening on each floor, which generated pressure fluctuations in the shaft. The airflow rate was suddenly increased to a positive value due to the created water hammer in the shaft at \(t=25.2\) s when the car was parked on the 15 th floor. After that, the airflow decreased gradually to a slightly negative value. At \(t=33.2\) s, the elevator car started to move downward, and the created positive pressure in the shaft pressed the air from the shaft to the lobbies. The airflow rate was relatively stable until \(t=56.6\) s, though some fluctuations in the airflow rates existed. When the car passed the protecting door's clearance opening on the second floor, the airflow rate decreased from a positive value to a negative one. Once the elevator car was parked on the first floor at \(t=58.4\) s, the water hammer was created again. The water hammer generated a sudden positive pressure in the shaft region above the elevator car, which pressed the air from the shaft into the lobby of the second floor. Then the airflow rate decreased to a negative value. After that, the airflow rate gradually increased and approached zero. Figure 15b presents the variation in the airflow rate at the protecting door's clearance opening on the seventh floor. The airflow rates with fluctuations corresponded to a stage with the motion of the elevator car. A positive airflow rate occurred when the elevator car was below the seventh floor, and the car moved upward, or when the elevator was above the seventh floor, but the car moved downward, and vice versa for the negative airflow rates. The sudden changes in the airflow rates were due to the elevator car passing the protecting door's opening on the seventh floor or because of the generated water hammers. The impact of the water hammer on the airflow rates was quite minimal eight seconds later since the parking of the elevator car. The above implied that the motion of the elevator car pressed the air from the shaft to the lobbies or sucked the air from the lobbies to the shaft, subjected to the created pressure in the shaft. The airflow rates swung with time due to the fluctuating pressure in the shaft when the elevator car intermittently passed the clearance opening on the protecting door on each floor.