# Comprehensive Optimization of Air Quality in Kitchen Based on Auxiliary Evaluation Indicators
## 4 Optimization Analysis of Kitchen Air Quality
### Simulation Results of Different Working Conditions
As shown in the figure, the air supply angle in condition 4 effectively reduced the CO\({}_{2}\) concentration in the breathing area during cooking to a maximum of 638 ppm, approximately a 24% reduction (about 220 ppm) from the maximum concentration under the original condition, reaching the clean air standard. In conditions 3 and 5, the CO\({}_{2}\) concentration trends in the breathing area were similar, both remained below 700 ppm, with a maximum concentration approximately 21% lower than that in the original condition. The average concentration trends throughout the room were consistent, primarily influenced by the exhaust from the range hood. The air supply angle in condition 5 effectively enhanced the CO\({}_{2}\) removal efficiency in the room, with a maximum concentration of 730 ppm, which is about 140 ppm, approximately 16% lower than the maximum concentration under the original condition. Figure 11: CO\({}_{2}\) concentration contours at cross-section x = 0.21 m and time 150 s under different conditions. Figure 12: Fitted scatter plot of CO\({}_{2}\) variation over time for different conditions. (**a**) Average concentration at breathing area of occupant; (**b**) Indoor average concentration. Figure 13 shows the spatial distribution of COFP at the time of 150 s under different conditions. The results indicate that COFP ascended to the upper part of the room with the thermal plume generated during cooking and formed a distribution pattern similar to an \"air lake\". Vertically, the COFP spatial distribution shows higher concentrations near the top and lower concentrations further down. At 150 s, the top air supply influenced the diffusion behavior of COFP. In condition 2, due to the smaller air supply angle, COFP primarily accumulated near the occupants' faces, adversely affecting air quality in the breathing area. In conditions 2 to 5, the angles of the air supply were less than 45 degrees relative to the vertical direction, causing some COFP to descend below occupants' waists. In condition 6, with a supply angle of 150 degrees, although the vertical transport of airflow was not pronounced, it still drove the transport of COFP \"attached\" to the air flow moved clockwise, reduced the COFP concentration near the occupants and improved overall air quality. COFP concentration is one of the key indicators for assessing air quality during cooking. Figure 14 presents a time-domain scatter plot of the average COFP concentration in the breathing area and the average concentration throughout the room under different conditions. As shown in the figure, the average COFP concentration in the breathing area is mostly below 50 \(\mu\)g/m\({}^{3}\), which is considered within a healthy range. However, due to the complex behaviors of COFP, such as coagulation, transportation, and deposition, the data in the breathing area exhibited significant fluctuations. The trend in the average concentration throughout the room remained relatively consistent, with no significant changes, indicating that the top air supply method had a limited effect on the removal of COFP. Figure 13: COFP concentration contours at x = 0.21 m cross-section at 150 s for different conditions. In the present study we employed numerical simulations to calculate time averages of different IAQ under different conditions. The overall assessment index Q was then determined using Equation (6). As shown in Table 9, the Q value throughout the kitchen initially increased and then decreased as the angle of the top air supply increased. In condition 4, when the air supply direction is 90\({}^{\circ}\), the IAQ throughout the kitchen was 1.401, which was the optimal configuration, representing a 26.9% reduction in Q value compared to the original condition. If the top air supply angle was either too large or too small, the Q value would exceed 1.5, indicating that the improvement in IAQ is not significant. When compared to the original condition, the Q value decreased only by 7.7% to 14.6%.