Articles
THE EFFECT OF SCREENS ON THE MICROCLIMATE OF GREENHOUSES AND SCREENHOUSES – A REVIEW
Article number
719_67
Pages
575 – 586
Language
English
Abstract
The use of screens to reduce insect entry into greenhouses has become a common practice in many countries.
The screens act as a mechanical barrier, aimed at preventing migratory insects from reaching the plants.
The physical exclusion of the insects from the greenhouse reduces the incidence of direct crop damage and also of insect-transmitted virus diseases.
Thus, the screens reduce the need for pesticide application; they allow growers to follow international mandatory regulations, enable the use of biological control agents as well as the use of insect pollinators and contribute to the protection of the environment.
The exclusion of very small insects is achieved by installing fine mesh screens across the greenhouse openings.
Since the porosity (ratio between open and total areas) of these screens is usually low, they impede ventilation and reduce light transmission.
Therefore, it is important to determine their resistance to airflow and optical characteristics in addition to characterizing their obstruction to insect migration.
Studies have shown that screens that generated a higher pressure drop for a given approach air velocity in wind tunnel test, caused higher temperature and humidity within the greenhouse.
The high mesh insect-proof screens result in a reduction in the value of the discharge coefficients of the openings and thus reduce the ventilation rate and mean air velocity and turbulence level at the openings.
The screens generate smaller flow scales, and increase the spectral decay rate of the turbulent flow.
Furthermore, the air velocities within the greenhouse decrease resulting higher temperature and humidity gradients in the greenhouse.
The above mentioned problems can be addressed by increasing the openings area of the naturally ventilated greenhouses or by using forced ventilation.
When ventilation does not provide the desired air temperature artificial cooling systems, such as fan and pad or fogging system, need to be applied to maintain favorable conditions to plant growth.
The present study summarizes methods for characterizing pressure drop on screens.
It reviews the effect of screens on the microclimate of greenhouses and screenhouses and introduces the possible effect of incorporating screens into evaporative-cooled greenhouses.
The screens act as a mechanical barrier, aimed at preventing migratory insects from reaching the plants.
The physical exclusion of the insects from the greenhouse reduces the incidence of direct crop damage and also of insect-transmitted virus diseases.
Thus, the screens reduce the need for pesticide application; they allow growers to follow international mandatory regulations, enable the use of biological control agents as well as the use of insect pollinators and contribute to the protection of the environment.
The exclusion of very small insects is achieved by installing fine mesh screens across the greenhouse openings.
Since the porosity (ratio between open and total areas) of these screens is usually low, they impede ventilation and reduce light transmission.
Therefore, it is important to determine their resistance to airflow and optical characteristics in addition to characterizing their obstruction to insect migration.
Studies have shown that screens that generated a higher pressure drop for a given approach air velocity in wind tunnel test, caused higher temperature and humidity within the greenhouse.
The high mesh insect-proof screens result in a reduction in the value of the discharge coefficients of the openings and thus reduce the ventilation rate and mean air velocity and turbulence level at the openings.
The screens generate smaller flow scales, and increase the spectral decay rate of the turbulent flow.
Furthermore, the air velocities within the greenhouse decrease resulting higher temperature and humidity gradients in the greenhouse.
The above mentioned problems can be addressed by increasing the openings area of the naturally ventilated greenhouses or by using forced ventilation.
When ventilation does not provide the desired air temperature artificial cooling systems, such as fan and pad or fogging system, need to be applied to maintain favorable conditions to plant growth.
The present study summarizes methods for characterizing pressure drop on screens.
It reviews the effect of screens on the microclimate of greenhouses and screenhouses and introduces the possible effect of incorporating screens into evaporative-cooled greenhouses.
Publication
Authors
M. Teitel
Keywords
screens, discharge coefficient, porous media, microclimate, ventilation
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