The Ventilationjet system is used to dehumidify a greenhouse with a fully closed blackout screen during the night. Gerbera producer Zuijderwijk and Witzier in the Netherlands uses this equipment but was not satisified with the duhumidification capacity since the RH was rising to unwanted levels. That forced him to pull a gap in the screens but that resulted in local temperature drops and botrytis. In this research project the cause of the high humidity was found to be the result of a combination of unwanted transpiration from the floor area and a limited air supply through the screens as a result of a turbulent flow in the outlet of the fans. The problem was fixed by developing a new version of the Ventilationjet where the air was supplied through a vertical duct instead of a simple round opening in the screens. Also the air supply capacity was increased from 3 m3/m2.hr to 14 m3/ m2.hr with a speed controllable fan. In addition, measures were taken to prevent humid, warm air to reach the area above the blackout screen by guiding this air to a central opening in the screen above the concrete path in the middle of the greenhouse. The ventilation windows above this ventilation gap in the screen release this humid air to the outside world, without causing a temperature drop since the fans create an overpressure.
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