Plastic greenhouse Large greenhouse plastic greenhouse Introduction Large plastic greenhouse building structure Large plastic greenhouse covering material Large plastic greenhouse Ventilated plastic greenhouse window system Large greenhouse plastic greenhouse Introduction Large-scale plastic greenhouse is a rapid development of the past decade Kind of greenhouse form. Compared with glass greenhouses, its light weight, low use of skeleton materials, low shading of structural parts, low manufacturing cost, long service life, and environmental control ability can basically reach the same level of glass greenhouses, so its user acceptance capability is around the world. Far above the glass greenhouse, it has become the mainstream of modern greenhouse development. The development of large-scale plastic greenhouses is directly related to the development of transparent plastic films or plastic plates. The combination of agriculture and plastics industry has produced a variety of greenhouse-specific membranes, and high-strength composite membranes have basically reached every user. With the further development of plastic film, greenhouse membrane selection has been directly related to greenhouse planting species. According to the requirements of light quality and light quantity of different cultivated crop objects, selecting or replacing plastic film according to the changes of the four seasons climate can better adapt to crop growth. The request. The versatility of the plastic film makes the greenhouse film more oriented to the development of multi-layer composite films. Longevity, non-dripping requires the plastic film to absorb or reflect ultraviolet rays strongly on the outer surface, and the inner surface can be long-lasting. In addition, in order to prolong the service life of the film, especially to reduce the decrease in the transmittance, the plastic film also uses a variety of compounding agents on the outer surface of the film to remove static electricity, dust, and acid rain, so that the service life of the plastic film is improved. Greatly improved. Recent developments have shown that the production of thin films with a service life of 5 to 10 years does not involve much technical difficulties. However, the prices are still high on the market at the current stage, and it is necessary to further improve the formula and reduce the cost. The use of plastic films in greenhouses also makes the design of greenhouse structures more flexible. Designers can make full use of the plastic film flexibility is good, can be adapted to the characteristics of various shapes of greenhouse structure, design different styles of characteristics of the greenhouse type, the most typical of which is the natural ventilation greenhouse. The design of large-scale plastic greenhouses can be designed according to the streamline pattern of airflow to minimize the resistance of airflow movement. The design of an all-natural ventilation greenhouse, even if only by hot-pressure ventilation, the design ventilation volume can be similar to the basic ventilation every minute. The requirement to significantly reduce the operating costs of greenhouses also creates conditions for improving the market competitiveness of products in production. Ultimately, the reduction in production costs also benefits the majority of consumers. Although natural ventilation greenhouses have low operating costs and low one-time investment, they also have high requirements for operation and management. Because it is a passive environmental regulation greenhouse, its own regulation capacity is limited under conditions where the natural climate is not suitable. In the design, appropriate artificial environment control equipment should be configured according to the actual meteorological conditions in the construction area to realize the annual production of greenhouses. . In a well-designed naturally ventilated greenhouse, the indoor temperature level can be basically 3 to 5°C higher than the outdoor temperature. That is, under the condition that the outdoor temperature is lower than 30°C, natural ventilation can basically meet the growth requirements of various crops. Of course, there are few regions in China where the temperature is less than 30°C per year, especially in the summer. It is difficult to get through the hot summer production season simply by relying on natural ventilation. Therefore, the annual run of the greenhouse should be fully considered in the design. Cooling and warming in winter. In spite of this, natural ventilation must be used as much as possible in production operations, because in the annual production, weather conditions above 30°C for the whole year account for a minority, so reasonable natural ventilation design still has high economic value in production. . Large-scale plastic greenhouse building structure 1. Large-scale plastic greenhouse classification 1. According to the number of greenhouse greenhouses, the large-scale plastic greenhouses are divided into single-ridge greenhouses and joint-connected greenhouses. There are two-linked greenhouses, triple-linked buildings and multi-linked buildings in the joint-span greenhouses. Single-span greenhouses do not require drainage gutters. The snow load can generally slide off automatically and will not cause too much pressure on the roof. When ventilation is provided with side windows, the ventilation and cooling effect in summer is good. However, the greenhouses of a single building occupy a large area, the surface area of ​​the greenhouse is large, the amount of heat produced in winter is large, and the uniformity of the indoor environment is poor. The joint greenhouse basically overcomes the shortcomings of single-building greenhouses. When the total width is less than 30 meters, the ventilation effect in summer can basically reach the level of a single-building greenhouse. In indoor environment control, the same function as a glass greenhouse can be achieved. However, the cost is much lower than the glass greenhouse. Therefore, the plastic greenhouse will be the mainstream of the future development of greenhouse facilities. With the development and progress of materials, its comprehensive performance will certainly surpass the glass greenhouse. 2. According to greenhouse greenhouses and gables, plastic greenhouses are classified into straight-wall greenhouses and inclined-wall greenhouses. Inclined-wall greenhouses are generally inclined to the ground at the girder height side walls or gables. Due to the inclination of the side walls, it is particularly advantageous to resist wind loads. In winter cold regions, the use of vertical external wall columns in the greenhouse to add insulation curtains, can form the air insulation layer of the greenhouse envelope wall, which has a very beneficial effect on improving the overall thermal insulation performance of the greenhouse and the uniformity of the indoor environment. Opening the insulation screen in summer can increase the greenhouse planting area. However, it is difficult to install ventilation machinery in the inclined wall greenhouse. In order to obtain the wind-resistance effect of the inclined wall greenhouse, a stay cable is added to the entrance of the straight-wall greenhouse, which has good results in production. However, there must be a clear mark at the cable stay to avoid giving the production belt. To safety hazards. 3. According to the classification of greenhouse roofing plastic greenhouses can be divided into arch dome greenhouse, sharp roof greenhouse 1 - zigzag greenhouse and roof window greenhouse four. The zigzag greenhouse and the roof window greenhouse are all fixed vertical windows. The former has a ventilation window at the gutter and a large window area, while the latter has a ventilation window at the ridge and a small window. When the vertical vertical window is ventilated in summer, an insect net is generally provided at the window. From the ventilation effect point of view, due to the hot air of the greenhouse always moving upwards, and the negative pressure on the roof is also greater at the ridge, the combination of the side wall ventilation and the ventilation air pressure difference is also large. Therefore, it is similarly open. In the window area conditions, the roof window ventilation capacity is stronger than other ventilation windows. Fixed vertical windows, whether located at the ridge or at the gutter, can only be installed on one side of the roof of the greenhouse. Therefore, the design of the windows should be consistent with the prevailing wind direction of the local summer so that the greenhouses can be ventilated. A strong negative pressure develops at the mouth in order to strengthen the wind pressure ventilation in the greenhouse. At the same time, the dominant wind direction of the local winter should also be taken into consideration to avoid direct winter cold winds blowing into the greenhouse window, increasing the cold air infiltration in the greenhouse, and causing excessive heat loss in the greenhouse. In the zigzag greenhouse, ventilation windows are generally provided from the gutters, and the height of the ventilation windows does not reach the height of the roof. Therefore, two gutters must be installed in the greenhouse. This need has, to a certain extent, reduced the pressure of rainstorms on greenhouse drainage. However, special attention must be paid to the waterproofing of the eaves at the eaves to prevent the gutter from overflowing into the greenhouse. In roofed greenhouses, the slope of the roof at the roof is above 15°C. Most of the snow load on the roof of the greenhouse can slide directly onto the ground or the gutter, and due to the large height difference between the roofs, the space in the greenhouse naturally increases. This gives the greenhouse ventilation and indoor ventilation in summer. The even distribution of the environment has a more favorable side. However, due to the increase in the size of greenhouses, the amount of heat dissipation in winter has also increased; the timber used for greenhouse framework has also been correspondingly increased, but if it is indoors; the horizontal insulation screen is set below the gutter; in winter, the greenhouse cooling area will be basically the same as that of the arched roof greenhouse. Quite, through reasonable structural optimization, the total amount of wood used can also reach the level of other greenhouses. Arch dome greenhouses generally take the form of semi-circular or reasonably arched grid roofs. This kind of greenhouse has reasonable force and less timber, and it is widely used. Because the slope of the roof is relatively gentle, the effect of ventilation on the greenhouse in any place on the roof of the greenhouse is not too great, and the rack of the window opening mechanism will not be too long, which is conducive to the smooth transmission of the window opening mechanism. 4. Classification according to covering materials and their coverage Large plastic greenhouses can be divided into coil plastic greenhouses and sheet plastic greenhouses as well as single-covered greenhouses and double-covered greenhouses. In the coil plastic film greenhouse, the covering materials are mainly flexible plastic film materials such as PE, PVC, EVA, etc., whose thickness is 0.1-0.2 mm, light transmittance is over 90%, service life is more than 3 years, and generally not less than 2 years. . Sheet plastic greenhouse cover material is hard corrugated board or rigid porous structure board, corrugated board thickness of about 1 mm, porous structure board has double and triple structure, thickness from 8-20 mm, the service life is generally 10 More than a year. Due to the large one-time investment of the rigid plate relative to the coil, the cost of the full rigid plate plastic greenhouse is not under the glass greenhouse. To reduce the cost, most producers combine the rigid plastic plate with the flexible plastic.
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