The most accessible type of ventilation system in a Venlo greenhouse involves a rafter-rail device. This system operates the windows by means of rack and pinion mechanisms with push-pull bars. In this way, every roof size, panel size and ventilation window type can be fitted with the right mechanical apparatus, while being manufactured in conformity to standards. Ventilation system motors can be outfitted as desired, with standard rotating, polarity-reversible or frequency-regulated motors. The choice depends on the speed with which the ventilation system must be operated.
In case of wide-span greenhouses, the most widely used type of ventilation system involves a continuous mechanism: a shaft with pinions and racks operating the ventilation windows. You may choose a direct drive, where the motor directly moves the ventilation window, or an indirect drive, where one motor operates several ventilation windows by means of a reversible worm drive.
Both types of systems are available for plastic tunnel and Cabrio greenhouses: both the rafter-rail and continuous systems.
It is, however, extremely important to perform the calculations in order to determine the appropriate system. A number of factors play an important role here, including the size of the ventilation windows, the size of the greenhouse sections, the use of any insect screening and the wind load.