**4. Results**

#### **4.1 Vent configurations during sneezing**

Of all respiratory activities, sneezing is the most explosive and releases a large number of droplets with a high velocity. Droplets are carried over large distances and are one of the primary ways of spreading infection for airborne diseases like COVID-19. The simulation of sneeze particles in air is used to analyze infection risk associated with different vent configurations. Other respiratory activities such as talking and breathing at rest are suitable to study with the CFD modeling presented in Section 3. For a restaurant scenario, talking will be considered in Subsection 4.3 talking as a secondary source that could spread a virus.

#### *Assessing Ventilation Strategies to Reduce the Spread of Pathogens in Restaurants DOI: http://dx.doi.org/10.5772/intechopen.109634*

In the first part of the study, the COVID-19 carrier is seated in the restaurant at table (refer to **Figure 1**). The person sneezes across the table at an angle 30° downwards. The sneeze consists of 18,000 particles of which 2000 particles are classified as aerosols (0.5 *μ*m–5 *μ*m) and 16,000 particles as droplets (5 *μ*m–150 *μ*m). The diameter distribution for the particles was the same as that reported by Xie et al. [7]. A 5-minute flow simulation was completed with the ventilation turned on (ACH = 6) but without introducing particles to allow airflow in the restaurant to reach a quasi-steady state. This was used as the initial condition for the simulation with the sneeze particles for another 5 minutes. The sneeze particles were introduced at 14 s of this simulation. The sneeze lasted for 0.5 s with 1800 particles introduced every time step (Δt = 0.05 s).

The sneeze particles carried by the airflow in the room were either exhausted through the return vents or deposit on various surfaces in the room. Some particles deposit on adjacent tables and can potentially infect the people eating food placed on these tables. Also, any particle that remains airborne can pose a risk of infection for the restaurant patrons and staff. In 5 minutes, most of the sneeze particles are either exhausted or deposited. This is demonstrated in **Figure 3** which shows the time history for percentage of airborne particles. By the end of 5 minutes less than 10% particles are left airborne. This shows that 5 minutes is sufficient time to study the deposition of particles in the room.

The dispersion of particles throughout the room for the three vent configurations is shown in the **Figure 4**. Most of the particle dispersion took place within the first 2 minutes hence, smaller time intervals are chosen within the first three rows compared to the last two to get a better understanding of activity in the room. The first row (**Figure 4a**) shows sneeze particles after 20 s. There is not much difference between the vent configurations at this time. Sneeze particles rise up in a plume above the COVID-19 carrier. At 30 s (**Figure 4b**), sneeze particles have started to disperse horizontally for the Ceiling (S parallel) and the Ceiling (S staggered) cases but still stay in a vertical column for the Ceiling/Wall (S parallel) case due to the return vent being right above the table in the Ceiling/Wall (S parallel) case. At 60 s (**Figure 4c**), in the Ceiling (S parallel) and the Ceiling (S staggered) cases, sneeze particles are

**Figure 3.**

*Time history of airborne particles for ceiling (S parallel), ceiling (S staggered) and ceiling/wall (S parallel) vent configurations.*

#### **Figure 4.**

*Comparison of sneeze particle dispersion for ceiling (S parallel) (first column), ceiling (S staggered)(middle column) and ceiling/wall (S parallel)(third column) for (a) t = 20 s, (b) t = 30 s, (c) t = 60 s, (d) t = 150 s, and (e) t = 300 s. Red color represents aerosols and yellow represents droplets.*

carried backwards by the airflow from the supply vent above the patron and in the Ceiling/Wall (S parallel) case they are carried forward by the sneeze velocity. The sneeze particles have traveled farthest for the Ceiling (S parallel) case and are still relatively close to the patron in the Ceiling/Wall (S parallel) case. By 150 s (**Figure 4d**), the sneeze particles have dispersed all over the room for all three vent configurations but the concentration of particles is still highest near the patron in the Ceiling/Wall (S parallel) case. By the end of 5 minutes (**Figure 4e**), very few particles remain airborne. The number of airborne particles is highest for the Ceiling/Wall (S parallel) case.

*Assessing Ventilation Strategies to Reduce the Spread of Pathogens in Restaurants DOI: http://dx.doi.org/10.5772/intechopen.109634*


#### **Table 1.**

*Percentage of exhausted aerosols and droplets.*

**Table 1** shows a comparison of the percentage of aerosols and droplets individually exhausted to the return vents. The initial sneeze was modeled with 11.1% aerosols and 88.9% droplets. The percentage of aerosols exhausted is significantly higher than the percentage of droplets exhausted for all cases. This may be due to the fact that aerosols are lighter and tend to rise up and get carried by the airflow through the return vents. Droplets being heavier are not easily affected by the airflow and settle. Since the sneeze consists of a majority of droplets, a large percentage of the total number of particles are deposited on the floor while the percentage of particles exhausted is low.

**Figure 5** shows the percentage of particles exhausted through each vent. For the Ceiling (S parallel) configuration, the particles exhausted through each vent are evenly distributed. But for the other two configurations, most of the particles are exhausted through only one vent. This vent happens to be the one closest to the COVID-19 carrier, indicating that for the Ceiling (S parallel) configuration, the particles disperse through the entire room.

#### **4.2 Increasing air changes per hour**

The recommended number of air changes per hour (ACH) for restaurants is 6–12 to maintain adequate supply of fresh air necessary for the health of the occupants [18]. The results presented in Subsection 4.1 were for simulations when 6 ACH was maintained for each ventilation strategy. To understand the effect of ACH on the spread of particles in the room, in this section, three values of ACH are studied. The setup for this study is similar to Subsection 4.1 with regards to the location of the COVID-19 carrier and the sneeze particles. The Ceiling (S staggered) vent configuration was chosen as the reference case. ACH values of 6, 9 and 12 were maintained by changing the inlet velocity. The use of high-efficiency particulate air (HEPA) filters would slightly alter the ACH but is not considered explicitly as the three cases cover a wide range of possible values. The inlet velocities for 6, 9 and 12 ACH are 2.77 m/s, 4.15 m/s and 5.54 m/s, respectively. The dispersion of particles at the end of 5 minutes was compared.

The dispersion of particles are presented in **Figure 6** for 9 and 12 ACH respectively. These are compared to 6 ACH shown in **Figure 4** (middle column). At 20 s, not much difference can be observed between 6 ACH (**Figure 4a**, middle column) and 9 ACH (6 (a), first column), but for 12 ACH (**Figure 6a**, second column), sneeze particles are dispersed backwards due to the higher inlet velocity. At 30 s, compared to 6 ACH (**Figure 4b**, middle column), the sneeze particles have dispersed more in the 9 ACH and 12 ACH cases (**Figure 6b**). This trend continues in the next 30 s as shown in **Figure 4c**, middle column; and **Figure 6c**. In the 12 ACH case, a majority of the sneeze particles have traveled behind the sneezing patron. By 150 s (**Figure 4d**, middle column; and **Figure 6d**), sneeze particles

**Figure 5.**

*Percentage of sneeze particles exhausted through each vent configuration: (a) ceiling (S parallel), (b) ceiling (S staggered), and (c) ceiling/wall (S parallel).*

have dispersed throughout the room. For the 9 ACH and 12 ACH cases, majority of the particles have been carried behind the patron due to higher inlet velocity from the supply vent above the patron. At 300 s, most of the particles have either been exhausted to the return vents or deposited on various surfaces. Very few particles are still airborne. The number of airborne particles are highest in the 6 ACH case and lowest in the 12 ACH case (**Figure 4e**, middle column; and **Figure 6e**).

**Figure 7** shows the trend of airborne and exhausted particles with increasing ACH. The percentage of exhausted particles is highest for 9 ACH (8.81%) but decreases to 3.27% for 12 ACH. The higher downward velocity for 12 ACH pushes the particles towards the floor which is why the percentage of exhausted particles is lower and a larger number of particles are deposited on the floor. As the percentage of exhausted particles first increases for 9 ACH and then decreases for 12 ACH, increasing ACH may not result in a higher success in removing virus from the room. On the other hand, percentage of airborne particles decreases with increasing ACH, posing lower infection risk for the occupants.

#### **4.3 Talking**

The previous scenarios investigated one COVID-19 carrier at a fixed location. However, in a restaurant there are multiple people who release respiratory particles regularly due to various activities like talking and breathing. In this section, two vent configurations are compared for a scenario involving multiple people talking. **Figure 8** shows the people who talk within the duration of the simulation marked in red. Simulations for the Ceiling (S parallel) and Ceiling (S staggered) cases are compared for multiple people talking for 5 minutes. The first instance of talking occurs at 5 s and all people finish talking by 2 minutes, with each person talking twice. During the rest of the simulation, the talking particles are dispersed throughout the room. The particles released during talking range from 0.1*μ*m to 10 *μ*m [6]. Each person released 40 particles during each second of talking. The people talking are chosen at random but at least one person is talking within an interval of 10 s.

The dispersion of talking particles in the room for the Ceiling (S parallel) and the Ceiling (S staggered) cases are shown in **Figure 9**. The people can be seen talking between 5 s and 120 s. At 15 s (**Figure 9a**), talking are particles released by the first two people seated at table-4. Since the first person talks in the forward direction,

#### **Figure 6.**

*Comparison of sneeze particle dispersion for 9 ACH (first column) and 12 ACH (second column) at (a) t = 20 s, (b) t = 30 s, (c) t = 60 s, (d) t = 150 s, and (e) t = 300 s. Red represents aerosols and yellow represents droplets.*

**Figure 7.** *Airborne and exhausted particles versus ACH.*

particles are carried forward by talking velocity in the Ceiling (S parallel) case but in the Ceiling (S staggered) case, forward motion of the particles is disrupted due to the air velocity from the supply vent above. By 45 s (**Figure 9b**), talking particles released by multiple people are dispersed throughout the room. A higher concentration of particles are near the person talking at table-1 (1d). Due to staggered vents, particles are more dispersed in the Ceiling (S staggered) case compared to the Ceiling (S parallel) case. By 75 s (**Figure 9c**), all 10 people have talked at least once and most twice. The talking particles are dispersed throughout room. There is not much difference between the two vent configurations. In the last two rows (**Figure 9d** and **e**), since there are not people talking anymore, the concentration of particles in the room decreases with time as they are exhausted or deposited.

In the sneeze scenario in Subsection 4.1, the exhausted particles were evenly distributed throughout the return vents for the Ceiling (S parallel) configuration and the same is the case for talking particles (**Figure 10**). For the Ceiling (S staggered)

#### **Figure 8.**

*Top view of locations for people talking. Supply and return vent on the ceiling are identified.*

#### **Figure 9.**

*Comparison of dispersion of talking particles for ceiling (S parallel) (first column) and ceiling (S staggered) (second column) for (a) t = 15 s, (b) t = 45 s, (c) t = 75 s, (d) t = 200 s, and (e) t = 300 s.*

**Figure 10.** *Percentage of talking particles exhausted through each vent: (a) ceiling (S parallel), and (b) ceiling (S staggered).*

case, while most sneeze particles were exhausted through only one vent, for talking, particles are more evenly distributed as the people releasing the particles are spread out across the room.
