ISHS Acta Horticulturae 578: International Symposium on Design and Environmental Control of Tropical and Subtropical Greenhouses
SIMULATION OF AIR FLUX AND TEMPERATURE PATTERNS IN A LARGE SCALE GREENHOUSE EQUIPPED WITH INSECT PROOF NETS |
| Authors: | H. Fatnassi, T. Boulard, L. Bouirden |
| Keywords: | greenhouse, ventilation, insect-proof nets, CFD, climate- modelling, TYLC. |
| Abstract:
Air flow, temperature and humidity patterns were simulated in a large-scale Moroccan type tomato-greenhouse (6000 m2) equipped with insect proof nets (6x6 meshes/cm2). Both momentum and energy equations were considered and the airflow’s in the crop cover together with the insect proof nets were described my means of the porous medium approach proposed by Darcy and completed by Forchheimer. The numerical resolution was performed using a Computer Fluid Dynamic’s finite (CFD) volume code with the PISO algorithm: CFD 2000. Three dimensional simulations were performed in stationary regime and the turbulent transfers were described by a standard k-  turbulence model.
The CFD code was customised in order to simulate also, within each mesh of the crop cover, the sensible and latent heat exchanges between the air and the crop (assimilated to the solid matrix of the porous medium). Flow, temperature and humidity patterns show that the air flow penetrates in the greenhouse through the windward end, it follows then a spiral trajectory, through the crop cover where it is warmed and humidified before rising over the crop and escaping through one part of the roof vents.
These air flow loops are fed by outside air penetrating in the greenhouse through the other part of the roof vents.
A reverse flow is observed near the leeward end and near the soil on the leeward half of the greenhouse.
These simulations were later validated with respect to air exchange rate measurements and a good agreement was observed between measured and simulated ventilation rates.
It is also shown that Computational Fluid Dynamics models can be satisfactorily used to study the spatial heterogeneity of climate inside the greenhouses (temperature, air speed, water) and to suggests design improvements for combining good ventilation performances and efficient protection again insects vectors of virus.
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