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

Abstract

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.

Advances in Computational Fluid Dynamics Applied to the Greenhouse Environment

“…Rico-García et al (2008) showed that ventilation in greenhouses due to the temperature effect produces high air exchange rates; however, those air patterns occur near the openings, causing almost no air exchange in the central zone of the greenhouse due to a stagnant effect that reduces the wind effect throughout the greenhouse. In agreement with the results of Majdoubi et al (2009), convection and radiation are the dominant forms of heat transfer. The measurements show that the difference between the air temperature inside and outside the greenhouse is strongly linked to solar radiation and secondly to wind speed.…”

“…Wind speed had a linear influence on air exchange rates, while the wind direction did not affect them. Majdoubi et al (2009) observed a strong wind air current above a tomato canopy that was fed by a windward side vent and a slow air stream flowing within the tomato canopy space. The first third of the greenhouse, until the end of the leeward side, was characterized by a combination of wind and buoyancy forces, with warmer and more humid inside air that was removed through upper roof vents.…”

“…Vera et al (2010a) observed that differences in temperature and ventilation rates strongly influence the movement of air, pushing it through openings where space is colder, while creating rising air currents when it is hot. Majdoubi et al (2009) showed that the buoyancy forces induced by air temperature and increased humidity result in loops of air between the crop and the roof windows, which in turn tend to accelerate the pace of removal of heat and water vapor, enhancing indoor climate. Fidaros et al (2010) studied turbulence in Greek greenhouses and found that external temperature variation is very important because internal temperature is determined by convection induced by the input current.…”

“…The climatic behavior of the rows of the tomato crop is taken into account using external user defined functions (Baxevanou et al, 2007). According to Majdoubi et al (2009), reorienting crop rows in simple ways improved climatic conditions. Endalew et al (2009) performed CFD modeling of a plant with leaves and branches of the canopy, using turbulent energy equations in porous sub-domains created around the branches.…”

Present and future of the numerical methods in buildings and infrastructures areas of biosystems engineering

“…CFDs can help designers in this task. A lot of papers have been recently published on this issue, many of them based on international research projects with collaboration of the countries with larger surfaces devoted to greenhouses such as Spain, Italy, Greece, the Netherlands, Israel or USA (Majdoubi et al, 2009;MolinaAiz et al, 2010).…”