Numerical study of wind-driven natural ventilation in a greenhouse with screens

This paper is devoted to the CFD study of wind-driven ventilation in a greenhouse, with particular focus to the effect of screens on the inner airflow distribution. Although the use of shading screens to cover agricultural crops has been constantly increased to reduce high radiation loads, their effect on airflow distribution within the greenhouse is still not fully understood. In this paper, CFD simulations of the ventilation in a greenhouse with and without screens are performed, by means of a finite volume CFD code (Ansys-Fluent 17.2), with a standard k-ε turbulence model, together with proper user defined functions (UDF) for the inlet velocity and turbulent profiles. The screens have been modeled as porous surfaces and the porosity and the permeability have been obtained experimentally and set into the model. The code has been validated by a comparison with velocity measurements performed in a greenhouse owned by the University of Bologna. Comparisons between the airflow velocity patterns obtained within the greenhouse with screens and without screens have been obtained for different external airflow velocities. The cases with screens show a more uniform distribution of velocity field inside the greenhouse than the cases without screens, especially near the crops. All the cases show that screens strongly affect the airflow velocity distribution inside the greenhouse and the distribution of volume flow rates through the vents. This work shows how the characteristics of the screens and their positioning near the vents are critical for the ventilation within a greenhouse.