## 3 Analyses of Environmental Parameters of Different Modular Wall Greenhouses
### Temperature Analysis inside the Greenhouses during the Test Period
#### 3.6.2 Energy Efficiency Ratio  
In this paper, the energy efficiency ratio K of the active heat storage cycle system was defined as the ratio of the total heat transfer in the storage and discharge phases to the power consumption of the axial fan operation in 1 d (9:00-9:00 the next day). The larger the energy efficiency ratio was, the better the energy saving effect was [7]. The energy efficiency ratio of the two kind greenhouses was specifically calculated according to the following equation [34]:  
\[K=\left|\frac{Q_{act}}{P\cdot t/1000}\right| \tag{6}\]  
where \(Q_{act}\) is the heat transfer in the storage and discharge phases of the active heat storage cycle system in the greenhouse (same as \(Q_{act}\) in Equation (2)), (MJ); \(P\) is the rated power of the axial fan, (kW), which is 0.025 kW for the two greenhouses with the same fan  
Figure 8: Change of the heat flux density of the greenhouse back wall. (a) Typical sunny day. (b) Typical cloudy day.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Module Type**} & \multicolumn{2}{c}{**Inlet Air**} & \multicolumn{2}{c}{**Outlet Air**} \\ \cline{2-5}  & **Temperature/\({}^{\circ}\)C** & **Relative Humidity/\%** & **Temperature/\({}^{\circ}\)C** & **Relative Humidity/\%** \\ \hline SG & 15.42 \(\pm\) 0.07 *** & 100.00 \(\pm\) 0.00 *** & 18.93 \(\pm\) 0.12 *** & 74.97 \(\pm\) 0.27 *** \\ PG & 13.65 \(\pm\) 0.36 & 87.51 \(\pm\) 0.69 & 17.96 \(\pm\) 0.17 & 68.90 \(\pm\) 0.66 \\ \hline \hline \end{tabular} Note: Different \({}^{*}\) in the same column mean a significant difference between treatments (\(p\) < 0.05, where \(p\) < 0.001 is ***).  
\end{table}
Table 5: SPSS significance test of the average air temperature and humidity of the air inlet and outlet on a typical cloudy day.  
specification; \(t\) is the operation time of the storage and discharge phases of the active heat storage cycle system, (s).  
The energy efficiency ratios of the two greenhouses for SG and PG were calculated as 92.12 and 79.55, respectively, in the heat storage phase on a typical sunny day and 16.78 and 15.21, respectively, in the heat release phase on a sunny day. In addition, 30.11 and 28.15 were the heat release phases on a typical cloudy day for SG and PG, respectively. This suggested that both SG and PG had a good energy saving effect in the three stages, among which the energy efficiency ratio in the typical sunny heat storage stage was higher than the other two stages. All the results indicated that the energy saving effect was better in this stage, which was due to the short duration and high heat transfer in the heat storage stage, so as to provide the heat release in the greenhouse at night. The lowest heat release stage was caused by the low heat release on sunny days and the long heat release duration. which increased the running time of the fan. The energy saving effect was lower than the other two stages, and then the energy efficiency ratio of SG was greater than PG in all three stages. This suggested that the energy saving effect of SG was slightly better than that of PG.