Opportunities of Ground Duct Ventilation in Greenhouses

Greenhouses in The Netherlands contribute significantly to the total energy consumption of the country. One of the leading Dutch philosophies for greenhouses is “the new growing” which reduce energy and improve health, quality and growing of plants: a greenhouse with an adaptive kind of comfort with a free running climate. Heating is necessary to prevent cold stress of plants or condensation. The relative humidity should be just low enough to prevent heat stress of plants or development of fungus. Ground ducts can reduce heating and cooling of air, reverse stratification, improve circulation and dehumidification. These ducts are heated up during the day by the air from the top of the green house, above the screens. In the thermal buffer of the ground solar heat is accumulated and released in the cold early morning. After measurements in a greenhouse with ground ducts, a calculation-model in Matlab is developed and validated. The diurnal temperature-swing in a ground duct is evaluated with the mathematic model of Hollmüller. Via the Matlab-model the energy savings and the effect of the amount and size of ground ducts can be predicted. The system has proved to create better developed tomatoes with almost no diseases anymore.