185 research outputs found

    CFD Simulation of Heat and Mass Transfer for Climate Control in Greenhouses

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    Greenhouse plant production involves a number of processes such as transpiration, condensation, photosynthesis, and climate control. Such processes, in turn, set off mass and heat transfer phenomena that influence not only the quality and quantity of crop production but also its environmental cost. While these processes have considerably been analyzed in separate, they strongly interact with one another. For instance, increased radiation (mainly thermal infrared) increases temperature, reduces humidity, consequently increases transpiration, and affects CO2 exchange as well as other reaction rates. Computational fluid dynamics (CFD) is a numerical tool with a solid physical basis which allows, through the construction of a computational model, to simulate the fluid flow environment. Heating, ventilation, and condensation have been analyzed in the greenhouse environment with CFD techniques. The current challenge is the interaction of these processes and their impact on the production system. The present work summarizes some CFD investigations carried out in this topic, in order to analyze the processes of heat and mass transfer in a greenhouse for agronomic purposes

    Modeling method of an active-passive ventilation wall with latent heat storage for evaluating its thermal properties in the solar greenhouse

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    Active-passive phase change heat storage technologies have been obtained extensive application to decrease greenhouse’s demands for fossil energy during off-seasons. To develop the utilization ratio of solar energy in solar greenhouses during winter, the active-passive ventilation wall with latent heat storage (APVW-L) was introduced and could be integrated into greenhouse’s back-wall. However, system design and operation parameters are subjected to numerous factors, including its structure, material performance and outdoor meteorological parameters. To achieve optimization in the energy performance of this system, this study used finite element analysis and lumped parameter analysis to establish coupled energy balance equations of the APVW-L and the air inside vertical air passages, and the cubic spline interpolation was used to calculate the continuous relationship between phase change material’s equivalent specific heat capacity and temperature. This modeling method of the APVW-L was accurately validated against the measured data, and then used in the optimization design and operation strategy of the APVW-L in the greenhouses. This study demonstrated that the optimized APVW-L could store 5.36 MJ/(m2·day) of solar energy in Beijing. Compared to the identical conventional greenhouses, after midnight, the experimental greenhouse having APVW-L increased the back-wall’s interior surface temperature by 2.2∼3.4 °C, and the average indoor air temperature by 0.8∼1.4 °C. This study provides methods for the APVW-L's optimization design and its operation strategy, even for the rationalization of the near-zero energy consumption of the solar greenhouse during winter

    Microclimatic behavior of a screen house proposed for horticultural production in low-altitude tropical climate conditions

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    In developing countries, horticultural production in low-altitude tropical climate conditions is often limited by biotic and abiotic factors. In these countries, the implementation of highly technical greenhouses is not feasible due to economic, social and cultural issues related to farmers. Therefore, one of the alternatives that has taken a great boom is the use of screen house structures (SH), although information on the microclimatic behavior of these is still limited. The objective of this research was to use an experimentally validated 3D CFD numerical simulation model to study the thermal behavior and airflow patterns in an SH located in the Colombian Caribbean region during the daytime hours (6:00 to18:00 h). The results obtained showed that the air flow patterns inside the SH showed speed reductions of up to 68% with respect to the speed of the external wind. It was also found that the thermal behavior inside the SH was quite homogeneous, the average temperature values in the structures ranged between 23.9 and 39 °C and the difference with external environment temperature did not exceed 1.8 °C. It was concluded that the implementation of this type of structure could be an useful technological tool for the optimization of horticultural production in low-altitude tropical climate regions.In developing countries, horticultural production in low-altitude tropical climate conditions is often limited by biotic and abiotic factors. In these countries, the implementation of highly technical greenhouses is not feasible due to economic, social and cultural issues related to farmers. Therefore, one of the alternatives that has taken a great boom is the use of screen house structures (SH), although information on the microclimatic behavior of these is still limited. The objective of this research was to use an experimentally validated 3D CFD numerical simulation model to study the thermal behavior and airflow patterns in an SH located in the Colombian Caribbean region during the daytime hours (6:00 to18:00 h). The results obtained showed that the air flow patterns inside the SH showed speed reductions of up to 68% with respect to the speed of the external wind. It was also found that the thermal behavior inside the SH was quite homogeneous, the average temperature values in the structures ranged between 23.9 and 39 °C and the difference with external environment temperature did not exceed 1.8 °C. It was concluded that the implementation of this type of structure could be an useful technological tool for the optimization of horticultural production in low-altitude tropical climate regions

    Thermal performance of an active-passive ventilation wall with phase change material in solar greenhouses

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    © 2018 Elsevier Ltd Using phase change material (PCM) in the north wall of solar greenhouses has been recommended as an efficient solution for promoting their indoor thermal environment. In this type of walls, however, there is always a thermal-stable layer, which would greatly decrease their heat storage capacity. To solve this problem, an active-passive ventilation wall with PCM has been developed in this study, and a comparative study was carried out using both experimental and numerical methods to justify its advantages over conventional walls. Several important parameters have been monitored or calculated to reflect the contribution of the newly proposed method to the performance of the middle layer of the wall, the indoor thermal environment and the plants’ growth. The obtained results confirmed the great effectiveness of the proposed wall in promoting the temperature of its middle layer and irradiated surface. In the newly proposed wall, there was no thermal-stable layer observed, resulting in a minimum temperature rise of 1.34 °C. The proposed solution also enhanced the wall's heat storage capacity by 35.27–47.89% and the heat release capacity by 49.93–60.21%, resulting in an average increase of indoor air temperature, daily effective accumulative temperature and soil temperature by 1.58–4.16 °C, 33.33–55.06% and 0.53–1.09 °C, respectively. The plant height, stem diameter and fruit yield have been increased by 30%, 25% and 28%, respectively

    Contribution to the sustainability of agricultural production in greenhouses built on slope soils: a numerical study of the microclimatic behavior of a typical Colombian structure

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    This is the final version. Available from MDPI via the DOI in this record. The use of covered structures is an alternative increasingly used by farmers to increase crop yields per unit area compared to open field production. In Latin American countries such as Colombia, productive areas are located in with predominantly hillside soil conditions. In the last two decades, farmers have introduced cover structures adapted to these soil conditions, structures for which the behavior of factors that directly affect plant growth and development, such as microclimate, are still unknown. Therefore, in this research work, a CFD-3D model successfully validated with experimental data of temperature and air velocity was implemented. The numerical model was used to determine the behavior of air flow patterns and temperature distribution inside a Colombian passive greenhouse during daytime hours. The results showed that the slope of the terrain affects the behavior of the air flow patterns, generating thermal gradients inside the greenhouse with values between 1.26 and 16.93 ◦C for the hours evaluated. It was also found that the highest indoor temperature values at the same time were located in the highest region of the terrain. Based on the results of this study, future researches on how to optimize the microclimatic conditions of this type of sustainable productive system can be carried out

    Computational Fluid Dynamics (CFD) Analysis of Two Types of Greenhouse in Humid Climates in Optimizing Air Flow Distribution for Organic Food Production in Times of Pandemic

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    In a greenhouse we find multiple variables that have great impacts on crops, for this a CFD model is built to simulate microclimate distribution and obtain optimal climate control for the growth of the crop. Analyzes of solar heat gains, heat losses, and temperature and air distributions for each special moment provide a good guide for product selection. In the CFD simulation the greenhouse volume and wind speed will be obtained for an optimal temperature distribution. The time required for maintenance, the need for sensor calibration, natural deterioration, and unexpected failures will have to be taken into account. The analyzes show a comparison between various variations of the air flow velocity in 0.5 m / s, 1 m / s and 1.5 m / s in two different models of greenhouses, which we will obtain the optimal model for the development and elaboration of a greenhouse. Demonstrating the efficiency of CFD models for the design, simulation and application of greenhouses

    Study of the Effects of Vent Configuration on Mono-Span Greenhouse Ventilation Using Computational Fluid Dynamics

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    This is the final version. Available on open access from MDPI via the DOI in this recordThe rise in the human population, its density and scarcity of resources require cost effective solutions for sustainable energy and water resources. Smart and sustainable agriculture is one important factor for future green cities to tackle climate change as a cost-effective solution to save energy and water. However, greenhouses (GH) require consistent ventilation due to their internal temperatures, and this can be an energy-intensive operation. Therefore, it is necessary to analyse the potential factors involved. In this study, the effect of vent configuration of a mono-span greenhouse with roof and side vents at low wind speeds was investigated using computational fluid dynamics (CFD). The validated simulations were then performed on different models to analyse the effects of the vents’ locations on the ventilation requirements. The side vents were found to contribute most to the ventilation. The position of the side vent was found to affect the convection loop in the greenhouse and the air velocity at the plant level. The humidity was shown to be highest under the windward side vent. The roof vent was found to affect the temperature and air velocity in the roof of the greenhouse but had very little effect on the distributions at the plant level.British CouncilScience & Technology Development Fund (STDF) of Egyp

    Building Integrated Solar Thermal Systems. Design and Applications Handbook

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    Determinación del comportamiento térmico de un invernadero espacial colombiano mediante dinámica de fluidos computacional

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    En Colombia, la producción de flores se lleva a cabo en invernaderos de diferentes tipos y formas geométricas, pero con la una característica común de usar ventilación natural, para control de clima. En la actualidad, el conocimiento sobre el desempeño climático de estas estructuras es escaso. El objetivo del trabajo consistió en evaluar el comportamiento térmico de un invernadero espacial en condiciones de clima diurno y nocturno. La evaluación realizada, mediante modelado computacional, empleó la dinámica de fluidos computacional (CFD, en idioma inglés), aplicada a un invernadero dedicado a la producción de clavel (Dianthus caryophyllus), bajo las condiciones meteorológicas de la Sabana de Bogotá (Colombia). Este enfoque metodológico permitió obtener los patrones de distribución térmica en el interior del invernadero, encontrando que, para las condiciones meteorológicas evaluadas, el invernadero genera unas condiciones térmicas inadecuadas para el desarrollo del cultivo. La validación del modelo CFD, se realizó comparando los resultados de las simulaciones y las temperaturas registradas en el prototipo real del invernadero, obteniendo un grado de ajuste adecuado entre los valores simulados y medidos
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