## 3 Results and Discussion
Our screen analyses can help researchers and growers to choose the right screens according to their specific needs. For this reason, the heating energy demand of the different thermal screen materials available on the South Korean market were evaluated and compared. Their properties are described in Table 3. Figure 10 shows that Ph-77 combined with Ph-Super gives lowest least energy demand 139 MJ-m-2 compared with the others including Ph-77+Luxous, Ph-77+Polyester, Tempa+Ph-Super, Tempa+Ph-Luxous, Tempa+Polyester, which give demands of 142, 163, 145, 147, 171 MJ-m-2, respectively. This is due to the fact that Ph-77 and Ph-super's emissivity values are lower than those of the others. Our previous study [PERSON] et al. [28] and that of [PERSON] et al. [30; 36], on the sensitivity analyses of the effect of material properties on energy demand, confirmed these results. Greenhouse covering material is also an important factor, as there are many covering materials available on the market. It has a direct effect on the solar gain and the energy requirement of the greenhouse, and choosing the most appropriate one according to crop needs can help in minimizing energy costs [15]. Figure 11 shows the monthly heating and cooling demand of the most commonly used greenhouse covers including, PE, PVC, HG, PC, PMMA. All the conditions were same as in the \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Maximum Heating Load**} \\ \hline \hline  & **Load (MJ\(\cdot\)h-1-m-2)** & **Outside Temperature (\({}^{\circ}\)C)** & \multicolumn{2}{c}{**Outside Solar**} \\  & & & **Radiation (kJ\(\cdot\)h-1-m-2)** \\ \hline Without screen & 0.65 & \(-\)10.7 & 0 \\
1 screen & 0.46 & \(-\)10.7 & 0 \\
2 screens & 0.41 & \(-\)10.7 & 0 \\
3 screens & 0.34 & \(-\)10.7 & 0 \\ \hline \hline  & \multicolumn{3}{c}{**Maximum Cooling Load**} \\ \hline Without shading screen & 1.50 & 35.7 & 3570 \\ with shading screen & 1.18 & 35.7 & 3570 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Details of studied parameters. Figure 9: Screen control with outside solar radiation. previous analysis and only side walls were replaced with different covering materials. A comparison was made of the estimated energy demand for all of them. The PC-16 mm material gave the smallest heating demand of, 20%, 19%, 7%, 4% during the heating months (Jan, Feb, Mar, Nov, Dec) than the other materials.. Furthermore, PE gave the smallest cooling demand of 2%, 7%, 5%, 4%, lower than the others during summer months (June, July, August, September). Further analyses were carried out for the investigation of the effect of side wall multi-glazing on heating and cooling energy demand for the multi-span greenhouse. The triple-, double-glazing materials PC, and PMMA with different thicknesses available on the South Korean market were evaluated. Figure 12 depicts the results for triple-layered PC-16, and double-layered PC (10, 8, 6, 4 mm), and PMMA (16, 10 mm) thickness. Each sheet of material was 0.8 mm thick, and hence the total  
Figure 11: Monthly heating and cooling energy demand for the multi-span greenhouse using different greenhouse side wall covers. PE: Polyethylene, PVC: Polyvinyl chloride, HG: Horticulture Glass, PC: Poly carbonate, PMMA: Polymethylmethacrylate. Figure 10: Heating demand of greenhouse using different thermal screens. thickness depends on the air gap between two sheets. The results in Figure 12a showed that the smallest heating demand is for the PC-16 mm material, and that the heating demand increased significantly for lower thicknesses. This is due to the fact that a thicker material serves better in preventing heat loss. Moreover, PC-16 mm gave 4% less heating demand than PMMA-16 mm. In Figure 12b, the cooling demand trend is the inverse of the heating demand and the lower thickness of PC-4 mm showed the smallest cooling demand. This is due to the fact that a higher thickness will resist heat loss to the ambient weather, thereby causing the internal temperature of the greenhouse to increase more than with the thinner material.