## 3 Results and Discussion
### Simulation Cases for Greenhouse Model
#### 3.2.2 CO\({}_{2}\) Distribution toward on Sunny and Rainy Day Inside the Greenhouse  
Simulations under treatment of 1000 ppm of CO\({}_{2}\) concentration, that had been done in the previous study [34; 35] were conducted on a rainy day condition with PAR of 95 W m\({}^{-2}\)[36] and sunny day condition with PAR of 355 W m\({}^{-2}\) (based on NEDO solar radiation database).  
There was a minor change in the CO\({}_{2}\) concentration between sunny and rainy days, according to the CO\({}_{2}\) distribution (Figure 13). The effects of solar radiation on CO\({}_{2}\) distribution were slightly significant. The case of rainy day showed a slightly more even of CO\({}_{2}\) distribution inside the greenhouse than the case of sunny day. For the entire greenhouse, the quantitative evaluation of these results using CV shown in Table 6 is 18.1% for the sunny-day case and 15.6% for the rainy-day case. However, when it comes to the variability of CO\({}_{2}\) concentration inside the plant, sunny day (8.1%) and rainy day (8.7%) had essentially no effect on even the fluctuation of CO\({}_{2}\) concentration in the plant canopy.  
Figure 14 shows the net photosynthesis estimations of the greenhouse model under treatment of 1000 ppm of CO\({}_{2}\) enrichment on a sunny and rainy day. The simulation results of a rainy and sunny days revealed the mean values of net photosynthesis (PCFD) of 3.82 and 9.69 umol m\({}^{-3}\) s\({}^{-1}\), respectively. The value of the net photosynthesis results seemed reasonable according to the study of [PERSON] and [PERSON] [29] and [PERSON] et al. [37].  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Greenhouse**} & \multicolumn{2}{c}{**Plants**} \\ \cline{2-5}
**Parameter** & \multicolumn{4}{c}{**Weather**} \\ \cline{2-5}  & **Sunny** & **Rainy** & **Sunny** & **Rainy** \\ \hline
**SD (ppm)** & 81 & 71 & 38 & 41 \\
**Mean (ppm)** & 446 & 457 & 467 & 476 \\
**CV (\%)** & 18.1 & 15.6 & 8.1 & 8.7 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Coefficient of variations of CO\({}_{2}\) concentration in the case of sunny and rainy day.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Greenhouse**} & \multicolumn{2}{c}{**Plants**} \\ \cline{2-5}
**Parameter** & \multicolumn{4}{c}{**Side Vent**} \\ \cline{2-5}  & **Open** & **Closed** & **Open** & **Closed** \\ \hline
**SD (ppm) 1** & 80 & 71 & 41 & 41 \\
**Mean (ppm)** & 438 & 457 & 464 & 476 \\
**CV (\%) 2** & 18.2 & 15.6 & 8.8 & 8.7 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Coefficient of variations of CO\({}_{2}\) concentration in the case of side vents open and closed.  
Figure 14: Net photosynthetic (PCFD) inside the greenhouse: 1000 ppm of CO\({}_{2}\) enrichment cases on sunny and rainy day.  
Figure 13: The CO\({}_{2}\) distribution inside of the greenhouse in case the sunny and rainy day (image taken at cross-section 6 m from south wall).  
The PAR possibly compensated the CO\({}_{2}\) absorption through the photosynthesis process to be low at low light (rainy day) and was higher at high light (sunny day). Nevertheless, the different canopy layers such as the top layer (64%), middle layer (28%), and bottom layer (8%) were not assigned to the net photosynthesis as mentioned in the study by [PERSON] et al. [38] because in this simulation the dense of leaves were assumed to be homogenous for the whole plant. Thus, the net photosynthesis results were almost constant for the entire plant. However, according to the simulation results, this model may be appropriate to estimate the net photosynthesis average.  
The variability of CO\({}_{2}\) concentration inside the plant between a rainy and a sunny day determined practically no significant difference. Furthermore, these models revealed no significant connection PAR and even the variation in CO\({}_{2}\) content at the plants.