## 4 Results and Discussion
### Performance Prediction of Case CCKEF System under Various Conditions
#### 4.2.4 Different Exhaust Air Volumes  
The analysis results in Sections 4.2.1-4.2.3 show that when the system was operated at 11,726 m\({}^{3}\)/h (65% of the rated air volume), the purification efficiency met the standard requirements while the temperature in the cooking area was beyond the comfort range and pollutants spilled out on the left side against the wall. It was deduced that 11,726 m\({}^{3}\)/h was not the optimal operating air volume for the case CCKEF system. In this part, the effects of four sets of airflow conditions (50, 65, 80 and 100% rated airflow) on the indoor kitchen environment and the system purification efficiency were studied for three main simultaneous coefficient of stoves values (\(\varphi\) = 0.2, 0.6, 0.8). The results are shown in Figure 14.  
As seen in Figure 14, exhaust air volume had a significant effect on the temperature, air velocity, pollutant concentration and system purification efficiency. When the exhaust air volume was increased from 50% (9000 m\({}^{3}\)/h) to 100% (18,000 m\({}^{3}\)/h) of the rated air volume, the temperature in the cooking area decreased by about 4.5 \({}^{\circ}\)C, and the C\({}_{6}\)H\({}_{6}\) concentration decreased from 8 \(\times\) 10\({}^{-9}\) to 1.49 \(\times\) 10\({}^{-9}\) kmol/m\({}^{3}\). In the kitchen zone far from the cooking area, the temperature change was smaller, and the C\({}_{6}\)H\({}_{6}\) concentration decreased from 3 \(\times\) 10\({}^{-16}\) to 4 \(\times\) 10\({}^{-18}\) kmol/m\({}^{3}\) or less. The indoor air velocity increased significantly, with the increased rate of cooking area and kitchen zone far from the cooking area at 69.2% and 50%, respectively. The system purification efficiency decreased from about 93% to about 85%. Considering the indoor environment and system purification efficiency together, when the simultaneous coefficient of stoves was 0.2, and the exhaust air volume \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{1}{c}{**Case**} & \multicolumn{1}{c}{**NRAP–1**} & \multicolumn{1}{c}{**NRAP-2**} & \multicolumn{1}{c}{**NRAP-3**} & \multicolumn{1}{c}{**NRAP–4**} \\  & & **(Spring)** & **(Summer)** & **(Autumn)** & **(Winter)** \\ \hline \multirow{2}{*}{1} & T1 (\({}^{\circ}\)C) & 24.4 & 30.3 & 25.8 & 17.9 \\  & V1 (m/s) & 0.47 & 0.41 & 0.40 & 0.41 \\  & T2 (\({}^{\circ}\)C) & 22.3 & 29.3 & 24.3 & 12.9 \\  & V2 (m/s) & 0.46 & 0.40 & 0.39 & 0.51 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Temperature and velocity of natural transfer air from adjacent rooms in four seasons. was 80% of the rated air volume, the indoor temperature of the kitchen was comfortable, the pollutant concentration met the standard limit, and the purification efficiency was relatively high (90%). When the simultaneous coefficient of stoves was greater than 0.6, the exhaust air volume should be 100% of the rated air volume to keep the indoor temperature comfortable and guarantee the pollutant concentration, as well as the purification efficiency, meet the standard requirements. Therefore, in order to ensure the indoor and outdoor air environments meet the standards required under various working conditions, the case CCKEF system should operate at 100% of the rated air volume. The control of exhaust air volume under three scenarios (scenario a: CCKEF system is operated at constant measured airflow; scenario b: CCKEF system is operated at optimum airflow according to the simultaneous coefficient of stoves; scenario b: CCKEF system is operated at constant rated airflow) is shown in Figure 15.  
As shown in Figure 15, in actual operation, the case CCKEF system was operated at 65% of rated airflow constantly (scenario a). The energy consumption of scenario \"a\" was the lowest among the three scenarios, while the indoor environment was unsatisfactory from the above analysis. If the case CCKEF system was operated at the rated airflow constantly (scenario c), though the indoor and outdoor air environment can be guaranteed, the energy consumption was the highest.