Skylight, as one of the indispensable equipment for large scale greenhouse, is usually constructed at the top of the greenhouse roughly parallel to the roof ridge, and is made of the same material as the roof, which has a bracket that can be stuck at any position. The opening and closing of the skylight and its opening size can be controlled by the three control buttons of Open, Close and Stop according to the weather conditions and the greenhouse environment.
The side windows are usually located in the lower part of the greenhouse’s side walls that are perpendicular to the roof. They are mostly made of glass, which can be opened or closed by manual push and pull. When the temperature inside the greenhouse is too high, all doors and windows, including skylights and side windows, can be opened to allow natural ventilation and exchange of the air inside and outside the greenhouse to transfer indoor heat so as to achieve the purpose of cooling..
Taking into consideration that the high wind will blow off the skylight, the principle of hot pressure ventilation is usually adopted in actual practice, that is, cold air enters from the bottom side windows and hot air is discharged from the skylight, and the skylight and side windows are only opened when there is no wind or little wind. The decisive factors for ventilation volume include the height difference between skylights and side windows, and the size of vents.
II. Fan cooling pad system and precautions for installationand maintenance
For better natural ventilation, the skylights can be changed into fully-open roofs, and the side windows into automatic rolling curtains. The height of the greenhouse should be appropriately reduced, and the distance between the evaporative cooling pads and the ground should not be too high, usually 0.5-0.7 m or so. At the same time, the height of the evaporative cooling pad, negative pressure exhaust fan and seedbed apart from the ground should be kept consistent to the greatest extent, and the fans should be distributed as evenly as possible. The number of fans should be reasonably determined based on the greenhouse dimensions, fan air volume and plant cooling requirements. If its area does not change, the height of the greenhouse can be appropriately reduced to achieve the purpose of lessening the number of fans to saving costs and decrease energy consumption while ensuring the cooling effect. It is also feasible to reduce the number of greenhouse cooling fans by installing greenhouse cooling exhaust fans with large diameter blades and large air volume. The area of cooling pad has to be reasonably decided according to the number of greenhouse cooling exhaust fans. There should be no barrier between the cooling pad and the greenhouse cooling exhaust fan, the cooling pads are installed on the opposite of the greenhouse cooling exhaust fans, they are not in the same direction as the greenhouse doors. In normal circumstances, the cooling pad should be installed on the north wall of the greenhouse, and the greenhouse cooling exhaust fan on the south wall, and the gate is on the east and west sides.
For sake of safety, at least one side of the fan should be covered with a protective net to prevent birds or other small objects from being sucked into the fan by the suction generated when the fan rotates. Due to the loud noise and the automatic shutters of the greenhouse exhaust fan, the large airflow discharged from the greenhouse causes trouble to people passing by, so it is better not to set up the sidewalk beside the fan in design.
The cooling pad increases the humidity of the air in the greenhouse, which will affect plants that do not like high humidity. Moreover, too high humidity is harmful to the health of workers and easily causes joint disease or gout. In future, the expansion of greenhouse area will contribute to the trend of increasing cooling pad area. Therefore, workers should be well prepared for dampness and coldness.
III . High-pressure misting cooling and Precautions
High-pressure spray water should be pure water, and the nozzles should be regularly checked, cleaned and replaced. If the sunshade net spray is adopted, a better cooling effect can be achieved. Plants that like cool shade should be placed near the cooling pad, and tall close-planting seedlings with thick crown should not be placed in the greenhouse.
IV. Sunshade System and Precautions for that
Adequate sunlight is required in the greenhouse. Although the sunshade system comes with a certain heat insulation effect, it also reduces the sunlight on the plants at the same time. The lack of sunlight will cause succulents to grow unusually fast so as to affect their appearance, and some plants even cannot bloom normally due to lack of light. For some plants with ornamental leaves and flowers such as Hoya kerrii Golden Heart, the lack of sunlight will weaken their color. It is observed that the golden flower color on the leaves is weakened after 60% shading treatment. Therefore, the installation mode of the external sunshade net can be changed from parallel to the roof to parallel to the ground, thus to reduce the area of the sunshade net, that is, to decrease the damaged area.
Improvement tips: It is of great significance to summarize maintenance experience and observe plant phenology. The sunshade net with the corresponding shading coefficient should be selected based on the characteristics of different plants, and is opened and closed in time according to the weather conditions. In addition, the external sunshade net is susceptible to damages due to bad weather. Improvement method: The external sunshade net can be installed parallel to the ground instead of parallel to the roof to reduce the affected area.
Because of the serious limitations resulting from weather, the skylight cannot be opened in case that the wind is strong or it rains, and the opening size of the skylight on the same side is limited. Therefore, the future greenhouse development direction should be a fully open roof. The side windows are mostly manually pushed and pulled, and the opening size is limited. If there is a large number of side windows, it will inevitably waste manpower and affect work efficiency, so the automatic rolling curtain type will play a dominant role in the future.