Past year a fan was tested in a gerbera crop that pushes dry, cold air down through two layers of energy screen. Underneath was a second fan that mixes this air with warm greenhouse air.
This so-called Ventilationjet system made it possible for most of the nights to keep two screens completely closed.
Although thereby the RV rose to values above 90%, no moisture problems occurred. For the moisture control no minimum pipe temperature was used and the heat demand was also greatly diminished because of the much better insulation.
However, the average greenhouse temperature rose because after dusk it cooled down much slower and the temperature rises faster when the artificial light is switched on. That is why there is still often a crack pulled into the screen. This increases the chance of botrytis.
The solution is sought in increasing the air flow through the screen from 4 m3/m2/HR to 18 m3/m2/HR. Because in winter the larger volume of cold air would reduce the greenhouse temperature too much, a variable fan speed is introduced.
Now two departments are fully equipped with Ventilationjets, one with the old version and one with the new one. The coming autumn and winter shall indicate how that functions in comparison with a standard department.