Holland Gaas supplies custom mesh systems. Before being able to produce the materials to size, the windows are first measured. Gerdo Wennekers, operational manager at Holland Gaas, regularly heads out to do so. During the survey, he often discovers that ventilation windows in existing greenhouses are not properly adjusted. "It's a shame about the loss of ventilation," he says. "Normally an air window should be able to open twice as wide as the deck slope. However, we often find that the windows are set much lower."
And that is remarkable, because ventilation is one of the most important parts for a good and healthy cultivation. Wennekers: "A ventilation reduction of 20% due to incorrectly adjusted windows is unfortunately a regular occurrence." His advice is therefore: "For an optimal climate, check how the windows are adjusted in the greenhouse!" Naturally, Holland Gaas helps their customers with this.
Holding back
The use of mesh in the air windows prevents virus outbreaks and unwanted insects or birds from flying in. This allows for a healthy cultivation in a responsible manner. Pesticides are hardly or no longer needed. You would think this is ideal. Still, some growers are reluctant to install mesh in the vents, the main reason being the loss of ventilation.
Understandable, according to Wennekers. "But growers can often minimise the ventilation loss that mesh entails by initially adjusting the windows properly. In addition, mesh has the added advantage that ventilation can take place during rain."
Naturally, the advice remains to close the vents or set them to storm mode during a storm.
For more information:
Holland Gaas 
www.hollandgaas.nl
[email protected]