Canary greenhouse CFD nocturnal climate simulation

The aim of this paper is to predict in details the distributed nocturnal climate inside a one hectare Moroccan canary type tomato-greenhouse equipped with continuous roof and sidewalls ventilation openings with fine insect screens, by means of 3D CFD (Computational Fluid Dynamics) simulations by using a commercial Software package CFD2000 based on the finite volumes method to solve the mass, momentum and energy conservation equations. The turbulent transfers were described by a k-ε model. Likewise, the dynamic influences of insect screens and tomato crop on airflow movement were modeled by means of the concept of porous medium with the Boussinesq assumption. Atmospheric radiations contribution was included in the model by customising the plastic roof cover temperature deducted from its energy balance. Also, the CFD code was customized in order to simulate in each element of the crop cover the sensible and latent heat exchanges between the greenhouse air and tomato crop. Simulations were carried out with a wind prevailing direction perpendicular to the roof openings (west-east direction). Simulations were later validated with respect to temperature and specific humidity field measurements inside the experimental greenhouse. Also, the model was verified respect to global sensible and latent heat transfers. Results show that, generally, greenhouse nocturnal climate distribution is homogeneous along the studies greenhouse area. The insect proof significantly reduced inside airflow wind speed. But there is no significant effect on the inside air temperature and specific humidity respect to outside

Computational study of thermal performance of an unheated canarian-type greenhouse: influence of the opening configurations on airflow and climate patterns at the crop level

International audienceThe increasing cost of electricity often drives the famers of the countries of the southern shore of the Mediterranean, to adopt the natural ventilation in order to provide greenhouse aeration. The roof and sidewall vents are opened to allow the excess heat to escape and cooler outside air to enter during daytime. During night time, these openings are used mainly to regulate the excess humidity in greenhouse which causes damage on plants due to the development of Botrytis cinerea. This paper presents a computational fluid dynamic (CFD) comparative study of the effect of these roof and sidewall ventilation openings on airflow circulation and diurnal and nocturnal greenhouse climate distribution to assess their effect. The investigation was conducted in a one hectare canarian-type greenhouse, the most widely used in Morocco, with a mature tomato crop. The simulations were performed with the CFD model based on solving partial differential equations, which represent conservation laws for the mass, momentum, and energy, using CFD finite volume method (FVM). This CFD model takes into account the virtual crop as a porous medium using the Darcy-Forchheimer model restricted to its inertial terms. Simulation results show that opening configurations strongly affects the airflow circulation under the studied greenhouse, which can generate a heterogeneous climate at the canopy level, especially during daytime. Results have illustrated also that there is a reverse flow from the leeward end to windward end part of the greenhouse at the crop level. Closing the north-south sidewall ventilation openings contributes significantly to the inside air velocity increase which can decrease the diurnal air temperature at the crop level. Conversely, during night-time, climate distribution at the crop level is homogeneous on the whole greenhouse

CFD Modeling of the Microclimate in a Greenhouse Using a Rock Bed Thermal Storage Heating System

The rock bed heating system is a more cost-effective concept for storing thermal energy use in greenhouses at night during the cold winter season. This system is considered an environmentally friendly solution compared to conventional heating systems that rely on fossil fuels. Despite the abundance of research on thermal energy-based heating systems, only limited work on climate modeling in greenhouses using rock bed heat storage systems has been reported. To fill this research gap, this study aims to simulate the microclimate in a greenhouse equipped with a rock bed heating system using computational fluid dynamics (CFD) models. User-defined functions have been implemented to account for the interactions between the plants and the air within the greenhouse. Crop rows and rock bed blocks have been considered as porous media with their dynamic and thermal proprieties. The model’s accuracy was approved by comparing simulated and experimental climate parameter data from the greenhouse. The model’s ability to predict temperature, humidity, and air velocity fields in the greenhouse as well as in the rock bed system during both phases of energy storage and restitution was demonstrated. The thermal, dynamic, and hygric fields were accurately replicated with this numerical model. The growing zone had a vertical temperature gradient between the ground and the greenhouse roof, as well as high humidity. The distribution of temperature fields along the rock bed blocks showed a significant temperature gradient between the air inlet and outlet in the blocks during the two phases of heat storage and restitution. As a result, the model could be useful for sensitivity studies to improve the performance of this thermal storage heating system