No abstract

Global food production and availability in hot climate zones are limited by biotic and abiotic factors that affect agricultural production. One of the alternatives for intensifying agriculture and improving food security in these regions is the use of naturally ventilated greenhouses, an alternative that still requires information that allows technical criteria to be established for decision-making. Therefore, the objective of this work was to study the spatial distribution of temperature and relative humidity inside a greenhouse built in the Colombian Caribbean. The methodological approach included the implementation of an experimentally validated 3D numerical simulation model. The main results obtained allowed to determine that the airflows generated inside the greenhouse had average velocities below 0.5 m/s and were mainly driven by the thermal effect of natural ventilation. It was also found that the gradients generated between the interior of the structure and the exterior environment presented values lower than 2.0°C for temperature and −6.3% for relative humidity. These values can be considered low in comparison with other structures evaluated in other regions of the world where the gradients can reach values higher than 10°C and 13% for temperature and relative humidity, respectively.

RESUMENEn Colombia, la producción de rosa (Rosa sp.) se desarrolla en un alto porcentaje en invernaderos ventilados en forma natural. El objetivo de este trabajo consistió en desarrollar una caracterización del microclima generado en el interior de un invernadero a través de la modelación numérica de los flujos de aire mediante un software CFD (Computational Fluids Dynamics) de volúmenes finitos. El modelo CFD-3D utilizado fue validado mediante recopilación de datos experimentales, y se compararon datos experimentales y simulados, los que mostraron un grado de ajuste adecuado y una misma tendencia para las variables de temperatura y humedad relativa. Los resultados obtenidos muestran que para condiciones de clima diurno el microclima generado se encuentra en rangos óptimos para la producción de rosa. Para condiciones de clima nocturno, se observó una presencia constante del fenómeno de inversión térmica del aire interior del invernadero, lo cual genera condiciones subóptimas para el crecimiento y desarrollo de las plantas.Palabras clave: invernadero, simulación CFD, temperatura, humedad relativa, periodo diurno, periodo nocturno. ABSTRACTIn Colombia, roses (Rosa sp.) are mostly cultivated in naturally ventilated greenhouses. The objective of this work was to develop a characterization of the microclimate generated inside a greenhouse through the numerical modelling of air flows by using the CFD (Computational Fluids Dynamics) software of finite volumes. The CFD-3D model used was validated through experimental data collection and the results obtained from the comparison of experimental and simulated data, which showed a suitable degree of adjustment and the same tendency for the variables of temperature and relative humidity. The results obtained show that, for daytime conditions, the microclimate generated is in optimal ranges for the production of rose. For night-time climate conditions, presence of thermal inversion phenomenon in the indoor air of the greenhouse was observed, which generates suboptimal conditions for the growth and development of plants.

In tropical regions the production of ornamentals is developed exclusively in naturally ventilated plastic greenhouses, which sometimes leads to inappropriate microclimates with high temperatures and humidity that limit the productive development of plants. The aim of this work was to study air flows, temperature distribution and relative humidity inside an alternative greenhouse designed to produce rose (Rosa spp.). Three configurations of ventilation, side ventilation (SV), roof ventilation (RC) and combined roof and side ventilation (RSV) were analyzed. The methodological development was based on the use of a previously validated CFD-2D numerical simulation model, which showed an adequate fit between the measured and simulated data, obtaining MAE and RMSE values for temperature and relative humidity of 0.44 and 0.47 °C, 3.99% and 4.04% respectively. The results obtained for the predominant climatic conditions of the study region showed that the highest ventilation rates were obtained for RSV, with values of 0.044 and 0.182 m 3 m -2 s -1 , this ventilation efficiency propitiated the generation of a homogeneous microclimate, with temperature and relative humidity values adequate to produce rose (Rosa spp). ResumoEstudo da ventilação natural em uma estufa gótica multi-túnel projetada para produzir rosa (Rosa spp.) no trópico alto-andino. Nas regiões tropicais, a produção de plantas ornamentais é desenvolvida exclusivamente em estufas plásticas ventiladas de forma natural, o que significa que em algumas ocasiões microclimas inadequados são gerados com altas temperaturas e umidade que limitam o desenvolvimento produtivo das plantas. O objetivo deste trabalho foi estudar os fluxos de ar, a distribuição de temperatura e umidade relativa do ar dentro de uma estufa alternativa projetada para a produção de rosa (Rosa spp.). Três configurações de ventilação, ventilação lateral (SV), ventilação de telhado (RC) e telhado combinado e ventilação lateral (RSV) foram analisadas. O desenvolvimento metodológico baseou-se na utilização de um modelo de simulação numérica CFD-2D previamente validado, que mostrou um ajuste adequado entre os dados medidos e simulados, obtenção de valores de MAE e RMSE para temperatura e umidade relativa de 0,44 e 0,47 ° C, 3,99 e 4,04% respectivamente. Os resultados obtidos para as condições climáticas predominantes da região de estudo mostraram que as maiores taxas de ventilação foram obtidas para o RSV, com valores de 0,044 e 0,182 m 3 m -2 s -1 , essa eficiência de ventilação propiciou a geração de um microclima homogêneo, com valores de temperatura e umidade relativa adequados para a produção de rosa (Rosa spp.). Palavras-chave: Microclima, taxa de ventilação, simulação de CFD, temperatura, umidade relativa, volumes finitos.

The growing expansion of protected horticulture in many regions is occurring around densely populated areas where land for agriculture is scarce, expensive or is used for other purposes. Inexpensive plastic passively ventilated greenhouses are the common choice for protected cultivation in these developing regions. The objective of this work was to analyse the effect of surrounding constructions and natural obstacles on the thermal performance of two naturally ventilated greenhouses. A saw tooth type greenhouse (TCG), typical for Colombian production, and an optimised greenhouse (OG) alternative with greater ventilation areas were analysed using computational fluid dynamics (CFD) with and without the surrounding objects of a real environment. The results showed that air exchange rate of a greenhouse with restricted ventilation areas are greatly reduced when neighbouring objects are high enough. This ventilation restriction is intensified under low wind speed conditions. The temperature gradients of the OG greenhouse were lower than those of the TCG scenarios due to the increased ventilation rates. The rooftop ventilation index for the OG greenhouse was increased by 65% with respect to the TCG greenhouse index, resulting in a direct effect on the ventilation rates. An improved air exchange with the outside can be reached by increasing the greenhouse ventilation areas, especially the roof vents, to overcome the airflow restrictions imposed by the surrounding environment. This simulation exercise was validated with field temperature data collected for a real OG prototype built in the Bogota plateau, with results showing a similar pattern for the internal temperature gradient as exhibited by the CFD model.