Shading Screens Characterization by Means of Wind Tunnel Experiments and CFD Modeling

The use of shading screens in the protected cultivation sector is widespread, due to the fact they allow both to reduce the heat load and thus to control temperature, and to have lower and uniform levels of light intensity inside greenhouses. An extended selection of shading screens is available on the market, with different colors, material, and textures. The choice of the best screen depends on the specific application and needs of the grower. Despite the positive action of the screens, some screens can also negatively affect ventilation and indoor climate, since their porosity can generate extra mass, heat and momentum transfer resistance. Most studies have evaluated the screen-related parameters, such as permeability and porosity, and the screen effect on ventilation referring to screens with simple and regular textures, which is not the case of the new screen types. The reliability of the literature models for these parameters’ estimation of new type of screens is not certain. In this work, these parameters have been evaluated for three new screen types, available on the market, under different approaches. An experimental approach based on image analysis together with wind tunnel tests has been set up to yield the permeability and inertial coefficient. On the other hand, another methodology is based on the detailed modeling of the shading screen and on the CFD simulation to obtain the relation between air velocity through a screen and the relative pressure drop, avoiding any experiment. A representative section of the screen has been chosen for CFD simulations and the numerical results have been validated by comparison with Particle Image Velocimetry (PIV) data. This has allowed both to improve the model and to evaluate its effectiveness in simulating this specific fluid dynamics domain. By these novel approaches, the basis for extending the knowledge about the characterization of the screens used in agriculture have been laid