Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Insect-proof screens increase the resistance to ventilation flow across a greenhouse. The pressure drop across a clean 50-mesh screen is approximately 10 times the dynamic pressure of the approach velocity. While this is negligible relative to the pressure drop created by fans, it is a significant fraction of the wind-induced pressure drop. In naturally ventilated greenhouses, the problem is further aggravated by the accumulation of dust, which may increase the resistance of a screen by an order of magnitude.

Measurements in a 50m2 greenhouse showed that the loss coefficient of a 50-mesh screen increased from 12 when clean to 200 after two months of continuous fan ventilation. An approximate analysis of the problem showed that in naturally ventilated greenhouses, reduced ventilation due to dust accumulation, could double the intended temperature-rise.