Effect of the greenhouse design on the microclimate of greenhouses

What is it about?

Greenhouse design and cover material properties may strongly impact greenhouse energy. To study the effect of these parameters, three typical unheated agricultural buildings equipped with rows of canopy were considered, and two-dimensional simulations were conducted using the discrete ordinate model for simulating radiative transfers. Experiments were conducted to establish the boundary conditions and to validate the model. Two parametric studies were carried out: one for the nocturnal period when the energy performance of each type of greenhouse was investigated, and one for the diurnal period, when the sun path was simulated taking into account the type of the cover, its spectral optical and thermal properties. Results indicate that for the diurnal period, and for both plastic greenhouses equipped with fully opened side vents, the air located between the rows of canopy and ground surfaces remained very slow, not exceeding 0.2 m/s; for the Venlo glasshouse, the recirculation loop situated above the crop improved the air mixing and induced a good homogenization. Results also indicate that the cover material with the highest absorptivity, deteriorated the natural ventilation, increasing the air temperature by convection, enhancing local air temperature favoring the development of a secondary recirculation, and reduced the available photosynthetically active radiation. Concerning the nocturnal period, the ambient air temperature in the tunnel and in the vertical wall of the greenhouse was relatively homogenous and warmer than the temperature in the Venlo greenhouse. During the nocturnal period, the plastic greenhouse (in particular the one with the tunnel) performed better in regard to the homogenization of the climate and thermal energy storage.

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Why is it important?

for the diurnal period, for the Venlo glasshouse, the recirculation loop situated above the crop improved the air mixing and induced a good homogenization. The cover material with the highest absorptivity, deteriorated the natural ventilation, increasing the air temperature by convection, Concerning the nocturnal period, the ambient air temperature in the tunnel and in the vertical wall of the greenhouse was relatively homogenous and warmer than the temperature in the Venlo greenhouse. During the nocturnal period, the plastic greenhouse (in particular the one with the tunnel) performed better in regard to the homogenization of the climate and thermal energy storage.

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