Influence of Insect Screens with Different Mesh Sizes on Ventilation Rate and Microclimate of Greenhouses in the Humid Tropics

  Harmanto, H. J Tantau, V. M Salokhe

Abstract


An investigation on the effect of the use of nets with different mesh-sizes on the internal
microclimate and ventilation rate in greenhouses located on the humid tropics was carried
out. Three greenhouses (each measuring 10 m wide × 20 m long) were constructed and
covered with a plastic film on the roof, and different insect proof nets on the sidewalls,
respectively. Net sizes of 40-mesh, 52-mesh and 78-mesh were used. Water vapour,
transpired from 300 tomatoes cultivated in each greenhouse, was used to determine the
ventilation rate. In addition, an energy balance method which offers a simple, rapid and
accurate way to predict ventilation rate was developed based on common climatic data and
used in this study. A good agreement (R2 = 0.85) was obtained between two methods.
Statistically, the use of insect screens with different mesh-sizes had a significant effect on
ventilation rate and internal microclimate. The reduction of ventilation rate about 50% and
35% for the 78-mesh and 52-mesh greenhouses, respectively was obtained compared to the
40-mesh greenhouse. Consequently, the internal air temperature was also increased by 1 to 3
°C. Although, a small temperature difference was observed, the absolute humidity among
treatments was significantly different. The use of a higher mesh-size resulted in more
humidity. Ventilation rate and temperature rise in the greenhouses were strongly correlated to
the net porosity. Since their correlations were good in agreement, the simple equation derived
from the experiment will be very useful in predicting air exchange rate and temperature rise
when a new type of net is applied.

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