In the Netherlands the development of semi-closed greenhouses is going on for eight years. Increased carbon dioxide levels, reduced pesticide use, and energy saving are the main benefits of semi-closed greenhouses. Companies have developed several concepts with the goal to reduce the ventilation with outside air which mainly have been built at commercial tomato and Phalaenopsis growers. The goal of the project is to monitor the greenhouse climate at these nurseries in a uniform way so the concepts can be compared and to help growers to control the development of the crop in the best way. The climate is analyzed by measuring temperature and relative humidity on three heights: at the top of the canopy, in between the top and the root system, and near the full grown tomatoes. All system parameters regulating the greenhouse climate are registered which includes the air treatment unit used in the semi-closed greenhouse. Additional measurements are done to determine the local climate as a result of the air treatment units. Three concepts include air ducts below the hanging gutters which distribute outside air and/or cooled greenhouse air. Two concepts have air treatment units hanging above the canopy used for cooling. Only one concept is without windows and therefore completely relies on the systems for cooling. The systems with an air duct under the hanging gutters all show in a vertical temperature gradient with cold air near the root system and warm air near the top of the canopy. This gradient is not present in conventional greenhouses. The horizontal temperature distribution is rather homogenous during cooling with air ducts. Heating using the air ducts gives a lower temperature near the sides of the greenhouse than at the center of the greenhouse increasing the risk of botrytis. Coolers hanging above the crop give a homogenous climate during cooling. A disadvantage of these top coolers is the fact that they reduce the light level near the crop.
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