## 3 Results and Discussion
For the tunnel-type prototype, the N-oriented surfaces (e.g., \(s_{1}\) in Figure 3a and \(s_{4}\) in Figure 3b) received indirect solar radiation and should have a lower degradation rate compared to the other surfaces if the effect of solar intensity is only considered. However, the small size of the prototypes and the translucent nature of the film cover made all the cover surfaces receive solar radiation either directly or indirectly (after transmission through other surfaces). Consequently, deterioration of the film cover transmittance is attributed to the combined effect of solar radiation, dusty wind (i.e., common in the desert of Saudi Arabia; it happens several times a year), and film dirtiness (all the meteorological factors together). This effect, in general, drastically decreases the cover transmittance and increases the reflectance. The existing differences in the values of \(T_{s}\) among the different surfaces of the cover are also due to the direction of the dusty wind that is common at the site of the experiment. For the N-S-oriented duo-pitched roof cover (Figure 4a), the maximum difference in \(T_{s}\) values was 15.5% (between the N and E surfaces) and 12.2% (between the N and W surfaces) when the prototype was oriented E-W (Figure 4b). For the vertical surfaces of the duo-pitched roof cover, oriented either in the N-S or E-W directions, the maximum difference in \(T_{s}\) values was 10.5%. This difference is mainly attributed to the combined effect of the dusty wind direction and the other meteorological parameters (such as dust accumulation, solar irradiance intensity, etc.). In the case of calm and clear weather (solar irradiance effect was only considered), the degradation rate of \(T_{s}\) for the N surfaces is expected to be lower than that of the other surfaces because the N surfaces usually receive indirect solar radiation with low solar intensity. However, this trend is not clear in Figure 3a,b and Figure 4 a,b because the greenhouse prototypes were small in size and exposed to desert climatic conditions, and degradation of the cover optical properties was due to the combined effect of the mereological parameters, not only solar radiation intensity. both orientations (N-S and E-W). In Figure 6a,b, a maximum difference of 6-7% in the value of \(R_{\rm s}\) can be found among the surfaces of the duo-pitched roof cover when it was oriented in the N-S and E-W directions. During one-year exposure in the desert of the arid climate (the site of the experiment), the combined weather parameters (solar radiation, dust, wind speed, etc.) showed nearly the same effect on the reflectance (\(R_{\rm s}\)) increases in the different surfaces of each film cover. Reflectance is a surface phenomenon, and all the cover surfaces were exposed to the same weather conditions; therefore, the shape and orientation of the cover surfaces did not affect the reflectance value (\(R_{\rm s}\)). In order to explore the effect of the greenhouse shape and its orientation on the degradation characteristics of the transmittance of the film cover, the whole cover transmittance  
Figure 5: Variation of the sample reflectances (\(R_{\rm s}\)) affected by the exposure time for the tunnel prototype cover oriented in the N–S (**a**) and E–W (**b**) directions under arid climatic conditions. Figure 6: Variation of the sample reflectances (\(R_{\rm s}\)) affected by the exposure time for the duo-pitched roof prototype cover oriented in the N–S (**a**) and E–W (**b**) directions under arid climatic conditions. (\(T\)) was calculated as the average value of \(T_{\rm s}\) for the cover samples of each prototype (see Section 2.2). The degradation characteristics of \(T\) for both the tunnel and duo-pitched roof covers, oriented in the N-S and E-W directions, are depicted in Figure 7. Some variation was found in the values of \(T_{\rm s}\) among the different surfaces of the cover of each prototype.