1. The dead load of greenhouse construction refers to some weight caused by the dead weight of the fixed structure. The dead load can generally be based on the size, or simply look up the table. In actual manufacturing, many materials are newly developed and used and have no records and need to be tested. .
2. The crop load of greenhouse construction requires hanging various crops during the construction process of the greenhouse, and the space in the greenhouse is limited, so it is not possible to simply set up bamboo poles like in the open field. This load is higher than the crop load. Roughly calculated as 150N per m2, that is, the bed area is 1m2, and the crop load is 150N. When the horizontal line is first pulled on the frame and then hung, tension T occurs at the fixed point of the horizontal line. Therefore, the horizontal force at the fixation point must also be considered during design.
3. The snow load produced by the greenhouse is the vertical load on the roof. The degree of snow accumulation is not only related to the amount of snowfall, but also related to the shape and slope of the roof. The greater the roof slope and camber, the shallower the snow accumulation and the smaller the snow pressure. However, continuous-span roof gutters can easily form snowdrifts, increasing local snow pressure.
4. The wind load of greenhouse construction and the pressure exerted by wind on the building depend on the wind speed. Wind speed changes from time to time, and it can be expressed by two methods: average wind speed and instantaneous wind speed within a certain period of time. The former is often used in design calculations. Wind speed is also related to the height from the earth. The higher the distance from the earth, the greater the wind speed.
In the greenhouse construction structure, several loads of different natures are often affected at the same time. Their overall benefits and disadvantages to the structure should be considered. This is the question of the combination of greenhouse construction loads. The design load combinations of greenhouses and plastic sheds have the following conditions, and the unfavorable conditions should be used for design: dead load + snow load; dead load + wind load; dead load + live load (hoisting weight during building construction or repair) load); dead load + crop lifting weight.
5. The snow load of a greenhouse is the vertical load on the roof. The degree of snow accumulation is not only related to the amount of snowfall, but also related to the shape and slope of the roof. The greater the roof slope and camber, the shallower the snow accumulation and the smaller the snow pressure. However, continuous-span roof gutters can easily form snowdrifts, increasing local snow pressure.
Although the roof form of protective land buildings is similar to the structure of industrial and civil buildings, the roof covering materials are very different from those of industrial and civil buildings. In order to ensure the lighting requirements for indoor crop growth, glass, plastic film, etc. are used for coverage.
The covering material is thin and translucent, so indoor heat can easily be transferred to the snow through the covering material. In addition, the shape of the roof makes it easy for the snow to melt and slide off. In greenhouses used for winter production, the room temperature must generally be kept above 12°C. In this way, the snow can generally slide down automatically. Plastic greenhouses are rarely used in winter. If they need to be heated, the room temperature must not be lower than 5℃, and snow can generally slide off. When greenhouses used in early spring and late autumn are not heated, snow will not slide easily, but snow removal must be taken in time to meet the needs of light.
6. Calculation of large heating load in greenhouse construction: Large heating load is the basic data of heating design, and its size directly affects the economy of the entire facility.
7. Energy average of greenhouse production
A complete energy balance system includes solar energy and its transmission through covering materials, ventilation heat transfer, cold wind penetration heat loss, heat exchange with the earth, conversion of crop physiological and biochemical energy, long-wave radiation, and heat generated by staff and equipment. And heating system heating, etc. The maximum heating load of a greenhouse can be simplified as the energy requirement to average the heat loss of the facility through the enclosure layout and the cold air penetration.
8. Heat transfer consumption of greenhouse enclosure layout
The heat transfer amount of the greenhouse through its exposed surfaces can be calculated by the following formula: the heat transfer amount Q1 of the entire facility’s enclosure structure is the sum of the basic heat transfer amount q1 of each part of its enclosure structure.
9. The heat consumption of cold air penetration in greenhouse production
Under the influence of the pressure difference between indoor and outdoor caused by wind pressure and heat pressure, the cold outdoor air penetrates into the room through the cracks in the greenhouse, is heated and escapes. The heat consumed to heat this part of the cold air from the outdoor temperature to the indoor temperature is called the cold air penetration heat consumption.
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