Natural Ventilation Of Greenhouse Research Articles

Evaluation of wind-driven natural ventilation of single-span greenhouses built on reclaimed coastal land

Recently, the government of South Korea announced the construction plan for a large-scale greenhouse complex on reclaimed coastal lands. Wind characteristics of the coastal regions are quite different from those of inland. Natural ventilation of greenhouses is strongly dependent on the exterior wind characteristics; therefore, the effects of topographical and meteorological characteristics of the coastal regions on ventilation rate should be carefully evaluated to ensure stable and uniform production of the crops. In this study, wind-driven natural ventilation rates of single-span greenhouses were evaluated using a computational fluid dynamics (CFD) technique examining greenhouse type and typical wind conditions found in reclaimed lands. The accuracy of the designed CFD model was validated by comparing the result of the CFD simulation with the results of particle image velocimetry (PIV) measurements that were conducted in a wind tunnel. Furthermore, grid independence test and turbulence model test were conducted for validation of the designed CFD model. From these validated CFD model, the overall ventilation rates were estimated using two methods, mass flow rate (MFR) and tracer gas decay (TGD) methods according to greenhouse type, wind speed, wind direction, and configuration of the ventilator. Furthermore, local ventilation rates of the greenhouse were estimated using the TGD method. The CFD computed ventilation rates of greenhouses were evaluated by comparing them with the ventilation rates required for controlling the temperature in greenhouses. Finally, charts, which can be used to predict the natural ventilation rate of the single-span greenhouse built on reclaimed land, were developed.

Determinación de los patrones de flujo de aire en un invernadero multitúnel mediante anemometría sónica

En este trabajo se ha desarrollado una metodología para estudiar la ventilación natural en invernaderos mediterráneos mediante anemometría sónica. Los ensayos se han realizado en un invernadero multitúnel de tres módulos situado en el Campo de Prácticas de la Universidad de Almería. Esta metodología nos ha permitido obtener los patrones de ventilación natural del invernadero experimental para los vientos más comunes de la región. También nos ha permitido describir la interacción entre el efecto eólico y térmico, así como detectar deficiencias en la ventilación natural del invernadero debidas al efecto barrera de otro invernadero adyacente (provocando una reducción media en la velocidad del aire en el exterior de la ventana de barlovento de hasta el 98% para u, 63% para uy y, más importante, 88% para ux, la componente de la velocidad del aire que es perpendicular a la superficie de ventilación lateral). Los conocimientos adquiridos en este trabajo nos permitirán mejorar los algoritmos de control del sistema de ventilación. En este trabajo se realizan una serie de propuestas que podrían mejorar sustancialmente la ventilación natural del invernadero. Por ejemplo, se proponen algunas posibles modificaciones de la configuración de las ventanas laterales, buscando una mayor captación del aire exterior: se podría optar por ventanas dotadas de alerones exteriores que dirijan al aire hacia el interior o ventanas en las que la malla no se coloque directamente sobre la superficie lateral del invernadero, diseñando una antesala donde el aire pueda entrar sin la oposición de la malla. Otra propuesta sería prolongar la apertura de las ventanas laterales hasta el suelo, para favorecer así la entrada de aire a nivel del cultivo.

Natural ventilation of greenhouses: experiments and model

A theoretical and experimental study was conducted to investigate the transient response of the greenhouse air temperature and humidity, to the opening of roof windows. A theoretical model, based on non-dimensional mass and energy conservation equations was developed and similarity solutions were obtained. The model was calibrated against the results of experiments conducted in a full-scale greenhouse and the model parameters were identified. The study shows that opening the roof windows results in a decrease with time of the air temperature and humidity ratio and an approach to a steady-state. The effect of various physical parameters such as height of window opening, wind speed and solar radiation on the ventilation process, was studied by the model. The results show that the effect of the ventilation (i.e. the reduction in the temperature and humidity ratio within the greenhouse) increases with the height of the window opening and the wind speed, and decreases with the solar radiation.

A Study on Natural Ventilation of Greenhouse in Taiwan (II)

A Study on Natural Ventilation of Greenhouse in Taiwan (II)

A Study on Natural Ventilation of Greenhouse in Taiwan (I)

A Study on Natural Ventilation of Greenhouse in Taiwan (I)