## 4 Results and Discussion
### Performance Prediction of Case CCKEF System under Various Conditions
#### 4.2.3 Different Scenarios of Natural Transfer Air from Adjacent Rooms  
The replacement air of the case kitchen was natural to transfer air from the adjacent rooms, which is common in CKs. The natural replacement air parameters (NRAP) may be various in different seasons. Therefore, this section predicted the air velocity, temperature and pollutant distribution of the kitchen cooking area and the system purification efficiency based on measured replacement air temperature and velocity (Table 7), and the results are shown in Figure 13.  
Figure 13: The indoor air environment of cooking area and system purification efficiency under different natural replacement air temperatures (Q\({}_{\text{ex}}\) = 11,726 m\({}^{3}\)/h) **(a)** Air temperature; **(b)** Air velocity; (c) C6H6 concentration; **(d)** Purification efficiency.  
As seen in Figure 13a, the natural replacement air temperature had a greater effect on the kitchen indoor air temperature than the stove surface temperature. When the replacement air temperature was 22-26 \({}^{\circ}\)C (spring and autumn), the cooking area temperature was in the range of 22-30 \({}^{\circ}\)C, meeting the standard temperature requirements (18-32 \({}^{\circ}\)C). When the adjacent room temperature was 30 \({}^{\circ}\)C (summer), the temperature of the cooking area was within 29-38 \({}^{\circ}\)C, exceeding the high limit requirement in many places. When the make-up air temperature was 13-18 \({}^{\circ}\)C (winter), the temperature of the cooking area was in the range of 13-20 \({}^{\circ}\)C, and many places did not meet the low limit requirements. Therefore, commercial kitchens with only transfer air from adjacent rooms have a poor indoor thermal environment in summer and winter, and air-conditioned air needs to be installed to improve the thermal environment. As shown in Figure 13b, when the exhaust air volume was constant, the change in air velocity distribution of the cooking area under different seasonal scenarios was not obvious. The range of air velocity in the cooking area was 0.2-0.8 m/s, with an average of 0.5 m/s. The air velocity under the NRAP-4 scenario was a little higher, as the replacement air volume from door 2 was larger in the winter due to the higher temperature difference. It was deduced that the indoor air velocity was mainly influenced by the exhaust air volume. Figure 13c showed that pollutants spilled over and the concentration of C\({}_{6}\)H\({}_{6}\) in the cooking area exceeded the standard limit (1.49 \(\times\) 10\({}^{-9}\) kmol/m\({}^{3}\)) under NRAP-1 (spring) and NRAP-4 (winter) scenarios. Combined with Table 7, the transfer air velocity from adjacent rooms in these two scenarios was higher than in the other two scenarios. High transfer air velocity intensified the airflow disturbances, which was adverse for the hood capture performance, and then led to the overflow of cooking fumes. As seen in Figure 13d, the purification efficiency of the exhaust fume system was higher in summer than in other seasons, which may be due to the higher inlet temperature of the purifier in summer, which is conducive to trapping particles in the electrical purifier.