Natural Ventilation Performance of a Large Greenhouse Equipped with Insect Screens

Majdoubi, Hassan; Boulard, Thierry; Hanafi, A.; Bekkaoui, A.; Fatnassi, H.; Demrati, H.; Nya, M.; Bouirden, L.

doi:10.13031/2013.22653

Cited by 16 publications

(28 citation statements)

References 34 publications

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“…As simulation technology and computing power have improved, accuracy and realism in research based on CFD models, has increased as well, by defining more detailed models and by the use of textures that define the materials of the facilities. The use of insect-proof screens in commercial greenhouses is very important as a means of crop protection; even though they reduce natural ventilation, by this, there have been many research efforts to reduce its negative influence (Kittas et al, 2005;Harmanto et al, 2006;Majdoubi et al, 2007;Teitel et al, 2008a). These studies tested different designs in size of the box and tilt and determined the most affected areas within the greenhouse, where the use of porous media allowed its CFD simulation.…”

Section: Main Results Of Cfd Models In Greenhousesmentioning

confidence: 99%

“…Roy and Boulard (2005) simulated wind directions of 0 °, 45 ° and 90 ° with respect to the orientation of the greenhouse ridge to determine wind speed, temperature and humidity distributions inside the greenhouse, getting a good approximation for the humidity. In agreement with Demrati et al (2007), models allow estimation, with better accuracy, of water requirements for a banana crop under cover and improved water saving in regions where water is the main limiting factor for agriculture. Roy et al (2008) studied moisture on the surface of leaves at low light levels; crop transpiration and air flow were integrated into a single parameter model of leaf stomatal response to air flow and radiation.…”

Section: Incorporation Crop Effects and Crop Modelingmentioning

confidence: 95%

“…The heat and moisture transfer coefficients are deduced from the characteristics of the laminar boundary layer of the leaf, which are calculated with the velocity of flow in the crop. Khaoua et al (2006) found that under external conditions of 1 ms -1 air velocity and 30° of temperature, wind speed at crops' height varies according to the modalities of ventilation from the windward 0.1 and 0.5 ms -1 for the leeward side, while temperature differences ranged from 2.0 to 6.1 ° C. In a study with tomatoes, Majdoubi et al (2007) found that crop rows oriented perpendicular to air movement reduce the rate of airflow through the cultivation in a greenhouse by 50%. According to Baeza et al (2008), a greenhouse with natural ventilation efficiency must combine an enough number of air changes to remove excess of heat, with good circulation of air through the crop.…”

Section: Incorporation Crop Effects and Crop Modelingmentioning

confidence: 96%

“…In agreement with Harmanto et al (2006), using different screen's sizes over the vent opening has a significant effect, reducing 50% to 35% mesh 40, 78 and 52 and giving rise to a temperature gradient of 1 to 3 ° C with a mesh of 52 as optimal for a tropical greenhouse. Majdoubi et al (2007) found that insect-proof screens significantly reduced airflow, increasing thermal gradients inside the greenhouse by 46%. Using a wind tunnel with screens of different porosity (0.62, 0.52 and 0.4), Teitel et al (2008a) showed that a screen inclined by airflow reduces drag compared to a flow perpendicular to the screen, allowing an increase of 15-30% and 25% in the upper compared with a flat screen.…”

Section: Screens and Ventsmentioning

confidence: 97%

“…Roy and Boulard (2005) showed that the effects of wind direction on climate parameters inside the greenhouse are usually simulated by using different turbulence models available, to determine the energy balance between the flow of perspiration and the flow of radiation. Under ventilation parameters based on Bernoulli's theorem, Majdoubi et al (2007), showed that bad ventilation performance is not a result of the low value of the greenhouse wind−related ventilation efficiency coefficient, but rather, that the low rate of discharge due to pressure drop in air flow is generated both by the use of anti-insect screens with small openings as an obstruction due to the orientation of the rows of crops. Moreover, Rouboa and Monteiro (2007) note that the RNG turbulence model is best suited to simulate microclimates in arc-shaped greenhouses.…”

Section: Turbulence and Buoyancymentioning

confidence: 99%

See 4 more Smart Citations

Advances in Computational Fluid Dynamics Applied to the Greenhouse Environment

Flores-Velázquez¹,

Torre-Gea²,

Rico-García³

et al. 2012

Applied Computational Fluid Dynamics

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Section: Main Results Of Cfd Models In Greenhousesmentioning

confidence: 99%

Section: Incorporation Crop Effects and Crop Modelingmentioning

confidence: 95%

Section: Incorporation Crop Effects and Crop Modelingmentioning

confidence: 96%

Section: Screens and Ventsmentioning

confidence: 97%

Section: Turbulence and Buoyancymentioning

confidence: 99%

See 3 more Smart Citations

Advances in Computational Fluid Dynamics Applied to the Greenhouse Environment

Flores-Velázquez¹,

Torre-Gea²,

Rico-García³

et al. 2012

Applied Computational Fluid Dynamics

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Does insect netting affect the containment of airborne pollen from (GM-) plants in greenhouses?

et al. 2011

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Greenhouses are a well-accepted containment strategy to grow and study genetically modified plants (GM) before release into the environment. Various containment levels are requested by national regulations to minimize GM pollen escape. We tested the amount of pollen escaping from a standard greenhouse, which can be used for EU containment classes 1 and 2. More specifically, we investigated the hypothesis whether pollen escape could be minimized by insect-proof netting in front of the roof windows, since the turbulent airflow around the mesh wiring could avoid pollen from escaping. We studied the pollen flow out of greenhouses with and without insect netting of two non-transgenic crops, Ryegrass (Loliummultiflorum) and Corn (Zea Mays). Pollen flow was assessed with Rotorod® pollen samplers positioned inside and outside the greenhouse’ roof windows. A significant proportion of airborne pollen inside the greenhouse leaves through roof windows. Moreover, the lighter pollen of Lolium escaped more readily than the heavier pollen of Maize. In contrast to our expectations, we did not identify any reduction in pollen flow with insect netting in front of open windows, even under induced airflow conditions. We conclude that insect netting, often present by default in greenhouses, is not effective in preventing pollen escape from greenhouses of wind-pollinated plants for containment classes 1 or 2. Further research would be needed to investigate whether other alternative strategies, including biotic ones, are more effective.Electronic supplementary materialThe online version of this article (doi:10.1007/s10453-011-9237-8) contains supplementary material, which is available to authorized users.

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Airflow and microclimate patterns in a one-hectare Canary type greenhouse: An experimental and CFD assisted study

Majdoubi¹,

Boulard²,

Fatnassi³

et al. 2009

Agricultural and Forest Meteorology

131

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This study presents an analysis of air circulation and microclimate distribution during daytime in a 1-hectare Canary type tomato greenhouse in the coastal area of southern Morocco. The investigation of the climate inside the greenhouse is based on a numerical simulation using a finite volumes method to solve the mass, momentum and energy conservation equations. The main novelty of this simulation lies in the realism of the 3D modelling of this very large agricultural structure with (i) a coupling of convective and radiative exchanges at the surface of the plastic roof cover, (ii) simulation of the dynamic influence of the insect screens and tomato crop on airflow movement, using the concept of porous medium, (iii) simulation, in each grid cell of the crop canopy, of the sensible and latent heat exchanges between the greenhouse air and the tomato crop, and (iv) detailed simulation of climate parameters in a 1-hectare real-scale commercial greenhouse.The model simulations were first validated with respect to temperature and relative humidity fields measured inside the experimental greenhouse for fairly steady-state outside conditions marked by a prevailing sea breeze around the solar noon. A good agreement was observed between the measured and simulated values for inside air temperatures and specific humidity. It was next used for exploring the details of the inside air temperature and humidity fields and plant microclimates and transpiration fluxes throughout the greenhouse space. Simulation for a wind direction perpendicular to the side and roof openings shows that the insect screen significantly reduced inside air velocity and increased inside temperature and humidity, especially in the vicinity of the crop canopy. It revealed the details of the flow field within the greenhouse. At the windward end of the greenhouse, the flow field was marked by a strong windwise air current above the tomato canopy which was fed by the wind ward side vent, and a slow air stream flowing within the tomato canopy space. Then, from the first third of the greenhouse to the leeward end, the flow field was marked by the combination of wind and buoyancy forces, with warmer and more humid inside air which was evacuated through the upper roof vents, while colder and dryer air was penetrated through the upper roof vent openings. Based on these simulations, design studies of the greenhouse crop system were performed to improve inside air temperature and humidity conditions by simple modifications of orientation of the crop rows.

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Natural Ventilation Performance of a Large Greenhouse Equipped with Insect Screens

Cited by 16 publications

References 34 publications

Advances in Computational Fluid Dynamics Applied to the Greenhouse Environment

Advances in Computational Fluid Dynamics Applied to the Greenhouse Environment

Does insect netting affect the containment of airborne pollen from (GM-) plants in greenhouses?

Airflow and microclimate patterns in a one-hectare Canary type greenhouse: An experimental and CFD assisted study

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