Shading screens and ventilation efficiency in a naturally ventilated greenhouse by means of CFD modeling

The protected cultivation sector makes widely use of shading screens, considering the fact that they allow not only to reduce the heat load but also to control temperature and to reduce and level the internal light intensity of a greenhouse. A multiplicity of screen types is present on the market, with different colors, materials and textures. The specific choice of the screen depends on the application and needs of the growers, taking into account the solar-related characteristics of a screen. However, some shading screens can have also negative effects, in particular on the ventilation efficiency: low porosity textures can generate extra mass, heat and momentum transfer resistance. Their complicated and irregular texture can complicate the estimation of important parameters such as porosity and permeability, that are necessary to investigate and evaluate the effects they could have on the internal ventilation of a greenhouse. In this work, three screens type, available on the market, have been characterized by means of wind tunnel tests. The screen-related parameters, obtained from the experimental tests, have been used for investigating the effects on the natural ventilation of a glass greenhouse. A 3D CFD model of the greenhouse equipped with the screens has been performed (the model was validated in a previous work) and the simulations have been conducted for all the three screens under study. A comparative investigation on the internal fluid-dynamics has been conducted, in order to understand how the choice of a screen can affect the internal ventilation. The effects of the screens on the ventilation have been evaluated on the central area of the span. The screens proved to strongly affect the ventilation efficiency based on their different characteristics and properties of the screens.