Numerical Analysis of Heat and Mass Transfer in a Naturally Ventilated Greenhouse with Plants

Abstract

AbstractNatural ventilation is an efficient method that can maintain the microclimate in greenhouses at the required level for growing plants. This technique can also reduce the energy consumption required for mechanical ventilation. The aim of this study is to investigate heat and mass transfer inside a wind-driven naturally ventilated gable-roof greenhouse with plants in hot and dry climatic conditions using numerical modelling. The three-dimensional geometry of the greenhouse was created with Solid Edge ST10 software. The outdoor temperature and relative humidity were 27 ℃ and 10%, respectively. The air velocity at the greenhouse roof was 13.2 m s−1 and an atmospheric boundary layer profile was adopted for the inlet wind velocity. The greenhouse included one row of crops at the level of the openings. The crops were modelled as porous media. The porosity of the crops was 0.37. The simulations were performed using ANSYS Fluent 18.1 commercial tool. The Navier–Stokes governing equations were discretised by a finite volume method, and flow fields were estimated using the steady Reynolds averaged Navier–Stokes model in combination with the standard k–ε turbulence model. Variations of air temperature, relative humidity and turbulent dissipation rate (ε) of the air were analysed. The results of the study showed that air temperature inside the greenhouse increased by 1.2 ℃ as it approached the plants. On the other hand, an increase of 74% relative humidity of the air has was observed at the vegetation level due to the transpiration of the plants. The study also showed that the turbulent dissipation rate increased by 85% due to the amount of heat released by the plants that increased the turbulence of air. Future work should explore the effect of varying vegetation parameters on ventilation performance.KeywordsGreenhouseNatural ventilationCFD simulationTemperatureRelative humidityVegetation