In the research on the influence of air supply form of air conditioning system on the movement trajectory of indoor virus particles, this paper selects four air supply forms, namely top supply side lower return, side top supply side lower return, side bottom supply top return and seat armrest side upper return. For four different air supply forms, under the same personnel boundary conditions and wall boundary conditions, only change the positions of different air supply outlets and return outlets to study the distribution law of indoor air flow velocity, temperature and particle concentration. Firstly, under different operating conditions, the indoor temperature distribution law is shown in Fig. 5.
As can be seen from Fig. 5, no matter which air supply mode, the indoor temperature can be effectively reduced. However, for the temperature distribution in the environment around the human body, the air supply effect of scheme D is better than that of scheme ABC. In the first three air supply forms, due to the effect of wind speed and temperature, the personnel activity area in the room is divided into two parts, namely the left and right areas in Fig. 5. If the virus spreads rapidly between the left and right people, it will also cause the risk of infection for each person sitting in one area.
Similarly, through the simulation of the air velocity in the closed room, the results shown in Fig. 6 are obtained. It can be seen from Fig. 6 that the indoor space will always be divided into two independent parts due to the symmetrical structure of the room, whether it is upper air supply or lower air supply. When indoor personnel exercise less, the probability of cross propagation of the above two parts of air is small. However, the seat air supply is different. Because the air outlet is set at the armrest of the seat and the air outlet direction of the air outlet is perpendicular to the desktop, different people in the room can be effectively isolated through clean air, that is, a single person in different areas can be isolated at the same time, so as to reduce the risk of cross infection of people in the closed room.
After analyzing and studying the air parameters inside the closed space, the concentration distribution law of exhaled particulate matter is now studied. Figure 7 shows the results of the relative concentration of human exhaled virus particles. It can be intuitively seen from the figure that no matter which ventilation form is adopted, even the classic displacement ventilation, as shown in the result C in Fig. 5, is difficult to achieve better effective elimination of virus particles. When the personnel are sitting indoors, the virus particles exhaled by the personnel show an upward trend. The virus cleaning area can be realized below the personnel's mouth. However, with the floating effect of virus particles, the concentration of virus particles in the upper space gradually increases. At this time, when indoor patients stand or walk in during medical work, they just go into the upper pollution area, which will cause different degrees of exposure risk.
At this time, if the ventilation form of seat armrest is adopted, it can also be seen in the figure that it cannot solve the problem of upper and lower stratification of indoor virus pollutants, but it can preliminarily solve the risk of cross infection between sitting people on the same side.
In order to better compare the concentration distribution law of indoor virus particles, we select the space at the height of indoor personnel standing and sitting as the research object, that is, the space at the height of 1.75m in the Y direction; And the height space at 0.75m when people sit still; The concentration of virus particles in the subspace is statistically analyzed, and the results are shown in Fig. 8.
It can be seen from Fig. 8 that the concentration distribution of virus particles at different heights in the room presented by the four air supply modes is different. Firstly, in the y-week direction, mode C, i.e. down to up displacement ventilation mode, can achieve the lowest particle concentration in the middle area, but this area is not the place where people stay for a long time, but the environment in which external personnel or medical personnel often come in. The newly added seat ventilation forms show different distribution rules from the other three ventilation forms. In the surrounding environment of the sedentary personnel, the concentration of virus particles is relatively low, so it can effectively avoid cross infection between patients.
It can be seen from Fig. 9 that in the x-axis direction, that is, in the space of the patient's mouth during sitting, the virus particles show the law of fluctuating distribution. Among them, the traditional top air supply and bottom return forms can realize the uniform distribution of indoor virus particles, which cannot effectively realize the isolation between patients, such as scheme B. For the seat ventilation form, due to the relatively clean fresh air blown from the armrest of the chair, but the air exhaled from the space and the patient's mouth is clean, it is easy to realize the cross infection between the air. However, the polluted air can be quickly discharged in time in the space, so that the concentration of virus particles in the space is kept at a low position as a whole.
The air-conditioning air supply form inside the closed space will have an impact on the motion trajectory and distribution characteristics of indoor virus particles. The above analysis is aimed at aerosol particles in a relatively closed space. If the virus particles can maintain a high dose and activity indoors, it will cause infection risk to indoor healthy people.
In the enclosed space, even if the indoor infected person exhales the virus, as long as a reasonable and effective ventilation and air conditioning system is set, the indoor virus particle concentration is usually not too high, unless the ventilation and air conditioning system is set unreasonably, the ventilation effect is poor, the space is narrow and there are many infected people. It is the indoor virus concentration that causes the risk of personnel infection in the enclosed space, rather than the gas directly exhaled by the infected person. Moreover, according to the simulation analysis, the transmission path of exhaled particles from the human body is small, so it is difficult to realize the infection phenomenon of personnel at a distance of 1m away.
In the enclosed space, different forms of ventilation and air conditioning systems are set. When the transverse strong air flow is generated in the room, the concentration distribution of virus particles will show a roll like distribution, and the personnel inside the roll will cause new infection.
The above analysis shows that indoor air distribution may be an important factor in the transmission of virus. Avoiding the direct lateral flow of air around people's breathing area will reduce the diffusion of droplets between people. The air flow generated by the air conditioning system will affect the dispersion of droplets in the air. Evaluating and guiding the air flow to avoid blowing air from one person to another may reduce the risk.