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

Abstract 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- e 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.

[1]  D. Piscia,et al.  Shading screens for the improvement of the night-time climate of unheated greenhouses , 2013 .

[2]  J. Tanny,et al.  Wind driven ventilation of a mono-span greenhouse with a rose crop and continuous screened side vents and its effect on flow patterns and microclimate , 2008 .

[3]  Thierry Boulard,et al.  Effect of Vent Arrangement on Windward Ventilation of a Tunnel Greenhouse , 2004 .

[4]  Shaojin Wang,et al.  SE—Structures and Environment: Convective and Ventilation Transfers in Greenhouses, Part 2: Determination of the Distributed Greenhouse Climate , 2002 .

[5]  Stefano Benni,et al.  Efficacy of greenhouse natural ventilation: Environmental monitoring and CFD simulations of a study case , 2016 .

[6]  Pietro Picuno,et al.  Computational analysis of ventilation in greenhouses at zero- and low-wind speeds. , 1997 .

[7]  Rex Britter,et al.  Simulations of pollutant dispersion within idealised urban-type geometries with CFD and integral models , 2007 .

[8]  Thierry Boulard,et al.  Review: Effect of ventilator configuration on the distributed climate of greenhouses: A review of experimental and CFD studies , 2010 .

[9]  Meir Teitel,et al.  The effect of insect-proof screens in roof openings on greenhouse microclimate , 2001 .

[10]  Meir Teitel,et al.  Air exchange and ventilation efficiencies of a monospan greenhouse with one inflow and one outflow through longitudinal side openings , 2014 .

[11]  Tomas Norton.  CFD in the Agri-Food Industry: A maturing engineering design tool , 2013 .

[12]  Keshi He,et al.  Analysis of the Climate inside Multi-span Plastic Greenhouses under Different Shade Strategies and Wind Regimes , 2014 .

[13]  Timothy J. Barth,et al.  The design and application of upwind schemes on unstructured meshes , 1989 .

[14]  Thomas Bartzanas,et al.  Numerical simulation of thermal behavior of a ventilated arc greenhouse during a solar day , 2010 .

[15]  E. Rico-García.  Aerodynamic study of greenhouses using computational fluid dynamics , 2011 .

[16]  Thierry Boulard,et al.  Influence of an insect screen on greenhouse ventilation , 2002 .

[17]  Diego L. Valera,et al.  Measurement and simulation of climate inside Almerı́a-type greenhouses using computational fluid dynamics , 2004 .

[18]  Riccardo Buccolieri,et al.  Dispersion study in a street canyon with tree planting by means of wind tunnel and numerical investigations – Evaluation of CFD data with experimental data , 2008 .

[19]  Juan Ignacio Montero,et al.  A CFD greenhouse night-time condensation model , 2012 .