## 3 Results and Discussion
After successfully creating and validating the multi-span greenhouse BES model, simulations were carried out for all the multi-span greenhouse design parameters presented in Table 6 (simulation  
Figure 7: Computed versus measured internal air temperature of the greenhouse for validation in (**a**) summer, and (**b**) winter. section). Further analyses were conducted with the same greenhouse description and operating conditions presented in Table 5. (validation section). Only heating and cooling set points were changed to 18 \({}^{\circ}\)C and 30 \({}^{\circ}\)C for winter and summer, respectively. Firstly, we evaluated the effect of using a number of screens in the greenhouse during heating and shading screens during cooling, and made a comparison. Figure 8 shows the monthly heating and cooling energy demand when thermal and shading screens were used. The months for heating and cooling were selected based on South Korean weather and crop needs. In the periods November to March we used heating, while cooling was used for June to September. The results showed significant heat energy savings during the winter period by using screens and compared with the no screen greenhouse case. Moreover, when using three screens inside the greenhouse, the heat energy demand was 70% and 40% lower than when the single and double layered screens were used. Normally, in greenhouses, one or two thermal screens are used. [PERSON] et al. (2018, 2019), in two studies and our previous study ([PERSON] et al. (2019)) on the U-value of greenhouse cladding with thermal screens, reported that the use of thermal screens can reduce heating energy demand by 50-60%. [PERSON] et al. (2019) also reported a reduction in heating energy demand using thermal screens in comparison with cases without thermal screens. Their results are for the particular screens used in the current study, and can be different for other screen materials, as heat loss characteristics depend on the screen's properties. Furthermore, during summer months the shading screen showed 25% less cooling energy demand for the greenhouse. Therefore, during winter, thermal screens reduce heat loss to the ambient environment. Conversely, during summer, shading screens reduce the amount of solar radiation entering the greenhouse. This causes energy savings to be made and using screens in the greenhouse causes a volume decrease and hence a reduced energy demand. [PERSON] et al. (2019), who conducted a review on greenhouse shading for greenhouse energy savings improvement, and [PERSON] et al. (2019) who predicted the potential of different shading methods for greenhouses, also reported the same trend. In addition, Figure 9 shows the proposed model's capability in evaluating the thermal and shading screens effect on the greenhouse's energy demand under dynamic outside weather conditions and dynamic control of the screens (as in the real greenhouse). Further analyses were conducted to estimate the maximum heating and cooling demands for the reference multi-span greenhouse with and without screens, and the results are presented in Table 7. The maximum heating demand occurred at 8:00 a.m. on 9 January 2019 when the outside temperature was \(-\)10.7 \({}^{\circ}\)C and the solar radiation was 0 kJ-h\({}^{-1}\cdot\)m\({}^{-2}\). The maximum cooling demand occurred at  
Figure 8: Comparison of heating and cooling loads of the greenhouse using thermal and shading screens. 3:00 PM on 7 July 2019 when the outside temperature was 35.7\({}^{\circ}\)C and solar radiation was 3570 kJ-h-1-m-2. An estimation of the maximum heating and cooling demand of the greenhouse with fully controlled systems helps to design an energy providing facility for the greenhouse. [PERSON] et al. [34; 35] conducted two studies to estimate the maximum heating and cooling demand of a multi-span greenhouse to design a facility to fulfil its energy demand. They assessed the performance of the facility in fulfilling energy requirement in peak times. Different kinds of thermal screens are available in markets all over the world.