## 4 Conclusions  
This study proposed a multi-span greenhouse BES model utilizing the TRNSYS 18 program. We detailed the creation and validation of the BES model for multi-span greenhouses to simulate the thermal environment of the greenhouse under different design parameters. The model was used to evaluate the effect of the parameters on the annual energy demand of the greenhouse. The proposed BES model is capable of evaluating the multi-span greenhouse's design parameters with daily and seasonal dynamic control of thermal and shading screens, natural ventilation, as well as heating and  
Figure 19: Comparison of monthly solar radiation gain for selected greenhouse roof geometries. Figure 18: Comparison of monthly heating and cooling demand for selected greenhouse roof geometries. cooling set-points. The TRNSYS 18 program shows a high level of flexibility to carry out simulations under local weather conditions and can handle user-defined design and control of the greenhouse. The statistical analysis of the validated results encourages the adoption of the proposed model when the underlaying aim is to evaluate the multi-span greenhouse design parameters under local weather conditions and specific needs. The main findings of the study are as follows:  
* In winter, it is best use to three layers of thermal screens, as the analysis showed a 70% and 40% heat energy reduction compared with single and double layers of thermal screens. Moreover, the use of a shading screen in summer can reduce cooling energy demand by up to 25%. * The maximum heating loads of a multi-span greenhouse with conditions of without thermal screen, one screen, two screens, and three screens, were 0.65, 0.46, 0.41, and 0.344 MJ\(\cdot\)h\({}^{-1}\cdot\)m\({}^{-2}\), respectively. Moreover, the maximum cooling loads without and with shading screen were, 1.5, and 1.18 MJ\(\cdot\)h\({}^{-1}\cdot\)m\({}^{-2}\), respectively. * The Ph-77 thermal screen combined with Ph-super is more energy efficient and reduces heating energy demand during winter. * The PC-16 mm showed the smallest heating demands of 20%, 19%, 7%, and 4% during the heating months than the other materials and thicknesses studied. Furthermore, PE showed the smallest cooling demands of 2%, 7%, 5%, and 4%. This was lower than the others studied. * PC-16 mm is a more energy efficient double-glazed material than the other materials studied. * The E-W orientation has smallest annual energy requirement when compared with the other orientations considered. The result indicates that in January, the average daily solar gain of the E-W (0\({}^{\circ}\)) orientation was, 11%, 14%, 15%, 12%, and 7%; and it was higher than the 15\({}^{\circ}\), 30\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), 75\({}^{\circ}\), and 90\({}^{\circ}\) (N-S) orientations, respectively. Moreover, during June, the E-W (0\({}^{\circ}\)) orientation received 7%, 11%, 13%, 15%, and 15% less average solar gain than that of the 15\({}^{\circ}\), 30\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), 75\({}^{\circ}\), and 90\({}^{\circ}\) (N-S) orientations, respectively. * A 50% reduction in cooling demand was experienced during the whole summer season using natural ventilation combined with cooling. * Using north wall insulation during the day, a 5% reduction in heating energy demand was achieved during whole winter season. * The Verlo type greenhouse requires 25% less heat energy compared with the wide-span type and vice versa in the cooling season. The wide-span greenhouse requires 35% less cooling energy than the venlo type. Moreover, the solar energy gain of a wide-span greenhouse roof geometry is less than that of the venlo type greenhouse. Conceptualization, A.R., H.W.L., C.S.K. and H.T.K. ; Methodology, A.R., C.S.K., and H.W.L. ; Software, A.R., C.S.K. ; Validation, C.S.K. and H.T.K. ; Investigation, A.R., C.S.K. ; Resources, W.H.L. ; Writing--Original Draft Preparation, A.R. and C.S.K. ; Writing--Review and Editing, C.S.K., H.T.K. and H.W.L. ; Supervision, H.W.L.