Experimental Evaluation of the Loss Coefficient of Insect-Proof Agro-Textiles and Application to Wind Loads

Anti-insect nets are characterized by a very low porosity that determines a variation in the microclimate below the protection in terms of an increase in the relative humidity, a reduction in air ventilation, and a temperature rise. The air permeability of the textile depends on numerous factors such as the thickness of the wires, the size of the holes, the porosity, and the air velocity. The knowledge of this relationship would make it possible to optimize the size of the holes in order to maintain the anti-insect function with the increase in air velocity. The air permeability coefficients of 10 anti-insect nets were evaluated by means of a micro wind tunnel. The results showed that the loss coefficient is linked to the porosity (ε) of the nets: as the porosity increases, the loss coefficient decreases. The parameter that demonstrated the strongest correlation with the loss coefficient was the function of porosity h(ε) = (1 − ε2)/ε2. In the interval of porosity 0.10<ε<0.60, the linear regression correlation is quite high (R2=0.87). Finally, the reduction factor RF(ε)—an estimation of the reduction in wind pressure acting perpendicularly on the surface of a textile due to its porosity—was calculated and compared with that proposed by the Australian standard, which, currently, is the only international standard that explicitly considers the effect of porosity on wind action.