Greenhouse Project Solution

Oct 14, 2022

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In the season that is not suitable for plant growth, it can provide growth period and increase yield, and is mostly used for plant cultivation or seedling raising of warm vegetables, flowers, forest trees and so on in low temperature season. There are many types of greenhouses, which can be divided into many types according to different roof truss materials, lighting materials, shapes and heating conditions, such as glass greenhouses, plastic polycarbonate greenhouses; single greenhouses, multi-span greenhouses; single roof greenhouses, double greenhouses Roof greenhouse; heated greenhouse, unheated greenhouse, etc. The greenhouse structure should be sealed and insulated, but it should be easy to ventilate and cool down. Modern greenhouses have equipment to control temperature, humidity, light and other conditions, and use computer automatic control to create the best environmental conditions required by plants.

Greenhouse is a building that uses lighting covering material as all or part of the envelope structure material, and can be used for cultivating plants in winter or other seasons that are not suitable for open field growth.

historical origin

The origin of the greenhouse can be traced back to the period of Qin Shihuang. According to the scholar Wei Hong in the "Preface to the Ancient Civil Officials' Book of Zhao Ding", "Qin burned books, fearing that the world would not change the law, and all living beings would worship as Lang, before and after. Seven hundred people are secretly planting melons in the middle of the Lishan Mausoleum and Valley." The age of his life is based on burning books and cultivating scholars for more than 200 years, and his records must be based on word-of-mouth history.

Yan Shigu, a scholar in the Tang Dynasty, said in the commentary of "Han Shu, Volume 88, Rulin Biography 58" that "the place of wet soup in Xinfeng County today is called the town of Confucianism". The "place of wet soup" should be Wei Hong's statement that "the place in the middle of the Mausoleum and Valley of Lishan" further consolidates Wei Hong's credibility. Wei Hong's records about Qin Shi Huang reveal a piece of valuable agricultural technology information, that is, during Qin Shi Huang's time, the Chinese had invented greenhouse technology.

main classification

4 layers of greenhouse sun panels

Greenhouse function classification According to the end-use function of the greenhouse, it can be divided into production greenhouses, experimental (educational) greenhouses and commercial greenhouses that allow the public to enter. Vegetable cultivation greenhouses, flower cultivation greenhouses, and breeding greenhouses are all productive greenhouses; artificial climate chambers, greenhouse laboratories, etc. are experimental (educational) greenhouses; various ornamental greenhouses, retail greenhouses, commodity wholesale greenhouses, etc. are commercial greenhouses .

Greenhouses can be divided into film greenhouses, glass greenhouses, and plastic plate greenhouses according to their materials.

Plastic material

Large multi-span plastic greenhouse is a type of greenhouse that has appeared and developed rapidly in the past ten years. Compared with glass greenhouses, it has the advantages of light weight, less amount of skeleton material, low shading rate of structural parts, low cost, long service life, etc. Its environmental regulation ability can basically reach the same level as glass greenhouses, which is accepted by users of plastic greenhouses. The ability is far higher than that of glass greenhouses in the world, and it has become the mainstream of modern greenhouse development.

Plastic Greenhouse Structure

1. Overall dimensions of the plastic greenhouse

Such greenhouses have different structural dimensions in different countries. But in general, the span of the general greenhouse is 6m~12m, the bay is about 4m, and the eaves height is 3~4m. For multi-span greenhouses mainly based on natural ventilation, when the side windows and ridge windows are used in combination, the maximum width of the greenhouse should be limited to less than 50m, preferably about 30m; and for multi-span greenhouses mainly based on mechanical ventilation, the maximum width of the greenhouse can be Expand to 60m, but it is best to limit it to about 50m; for the length of the greenhouse, (from the perspective of ease of operation) it is best to limit it to less than 100m, but there are no strict requirements.

2. Main structure

The main structure of the plastic greenhouse is generally made of hot-dip galvanized steel pipe as the main bearing structure, which is factory-produced and installed on site. Due to the light weight of the plastic greenhouse itself, the resistance to wind and snow loads is weak, so the overall stability of the structure must be fully considered. Generally, vertical diagonal braces should be set in the second indoor span or the second bay. Necessary space supports should also be considered on the outer envelope and on the roof. It is best to have diagonal supports (oblique tie rods) anchored to the foundation to form a space stress system.

The main structure of the plastic greenhouse must have at least the ability to resist wind of grade 8, and the wind resistance of grade 10 is generally required.

The snow load bearing capacity of the main structure should be determined according to the actual snowfall conditions in the construction area and the winter use of the greenhouse. For use in the north, the design snow load should not be less than 0.35kN/square meter.

For plastic greenhouses in annual operation, load factors such as equipment weight, plant lifting weight, maintenance, etc. should also be considered.

glass material

A glass greenhouse is a greenhouse with glass as a transparent covering material.

Design requirements

Zhongnong scenery solar greenhouse

In the design of the foundation, in addition to meeting the strength requirements, it should also have sufficient stability and ability to resist uneven settlement, and the foundation connected with the support between the columns should also have sufficient horizontal force transmission and spatial stability. The bottom of the greenhouse should be located below the permafrost layer, and the heating greenhouse can consider the effect of heating on the freezing depth of the foundation according to the climate and soil conditions. Generally, the bottom of the foundation should be more than 0.5 meters below the outdoor ground, and the distance between the top surface of the foundation and the outdoor ground should be greater than 0.1 meters to prevent the foundation from being exposed and adverse effects on cultivation. Except for special requirements, the distance between the top surface of the greenhouse foundation and the indoor ground should be greater than 0.4 meters.

Independent foundation. Usually reinforced concrete is used.

Strip foundation. Masonry structure (brick, stone) is usually used, and the construction is also carried out by on-site masonry. A reinforced concrete ring beam is often set on the top of the foundation to install embedded parts and increase the strength of the foundation.

The steel structure mainly includes: the load-bearing structure of the greenhouse and the supports, connectors, and solid parts to ensure the stability of the structure.

The design of the steel structure of glass greenhouse in my country mainly refers to the greenhouse design specifications of the Netherlands, Japan and the United States. However, problems such as structural strength, structural rigidity, structural integrity and structural durability must be considered in the design.

Independent foundation. Usually reinforced concrete is used.

The steel structure mainly includes: the load-bearing structure of the greenhouse and the supports, connectors, and solid parts to ensure the stability of the structure.

Transparency

Greenhouse is a lighting building, so light transmittance is a basic index to evaluate the light transmittance performance of greenhouse. Light transmittance refers to the percentage of the amount of light that penetrates into the greenhouse to the amount of light outside. The light transmittance of the greenhouse is affected by the light transmittance of the greenhouse light-transmitting covering material and the shadow rate of the greenhouse skeleton, and with the different solar radiation angles in different seasons, the light transmittance of the greenhouse is also changing at any time. The level of light transmittance in the greenhouse has become a direct factor for crop growth and selection of plant varieties. Generally, the multi-span plastic greenhouse is 50%~60%, the light transmittance of the glass greenhouse is 60%~70%, and the solar greenhouse can reach more than 70%.

thermal insulation

Heating energy consumption is the main obstacle to the operation of greenhouses in winter. Improving the thermal insulation performance of the greenhouse and reducing the energy consumption is the most direct means to improve the production efficiency of the greenhouse. The thermal insulation ratio of the greenhouse is a basic indicator to measure the thermal insulation performance of the greenhouse. The greenhouse insulation ratio refers to the ratio of the coverage area of the greenhouse light-transmitting material with a smaller thermal resistance to the total area of the greenhouse envelope with a larger thermal resistance. The larger the thermal insulation ratio, the better the thermal insulation performance of the greenhouse.

Durability

Greenhouse construction must consider its durability. Greenhouse durability is affected by factors such as the aging resistance of greenhouse materials and the bearing capacity of the main structure of the greenhouse. In addition to its own strength, the durability of light-transmitting materials is also manifested in that the light transmittance of the material decreases with time, and the degree of attenuation of the light transmittance is a decisive factor affecting the service life of the light-transmitting material. Generally, the service life of steel structure greenhouse is more than 15 years. The design wind and snow loads are required to use the maximum load once in 25 years; the service life of the simple greenhouse with bamboo and wood structure is 5 to 10 years, and the design wind and snow loads use the maximum load once in 15 years.

Due to the long-term operation of the greenhouse in a high temperature and high humidity environment, the surface corrosion protection of components has become one of the important factors affecting the service life of the greenhouse. Steel structure greenhouse, the main structure of the force is generally made of thin-walled steel, which has poor corrosion resistance. In the greenhouse, it must be treated with hot-dip galvanized surface anti-corrosion treatment. life. For wooden structure or steel welded truss structure greenhouse, it must be ensured that the surface anti-corrosion treatment is carried out once a year.

type

safe

Environmentally Safe Greenhouse

Environmentally safe greenhouse is a closed type that can prevent plant diseases and insect pests without the use of pesticides or other chemicals, and can protect plants from harsh climate and physiological obstacles. Plant rearing facilities. Environmentally safe greenhouses are mainly divided into two categories: physical plant protection greenhouses and environmental control greenhouses. The former focuses on the configuration of physical control facilities for plant diseases and insect pests throughout the growth period. The latter is a greenhouse where pests and diseases, physiological obstacles, and growth environment regulation are all controlled. 1. Physical Plant Protection Greenhouse

The physical plant protection type greenhouse is mainly designed with the integrated system of physical plant protection technology as the core of the plant protection facilities, that is, the soil pest control is designed as the electric treatment mode of soil continuous cropping obstacles, and the airborne disease control of the aerial part is set as the greenhouse electric defogging and disease prevention and growth promotion system. The established space electric field control mode, the control settings for flying pests are the combination mode of color, light double lure and electric trapping and insect control net, and the red spider and other mites are the biological control mode or the perilla mite control mode.

control

Environmentally controlled greenhouses are based on physical plant protection greenhouses, supplemented by temperature, light, and carbon dioxide concentration control modes. It can still grow or preserve seedlings under extreme weather conditions. Auxiliary facilities for the growth environment include hot blast stoves or soil heating lines or wet curtains, space electric field generation systems, supplementary lights, and carbon dioxide application systems. In addition to preventing airborne diseases, the space electric field generation system also has the function of regulating plant photosynthesis. , which can enhance the photosynthesis intensity of plants in low-light environments.

sunroom

The front slope is covered with thermal insulation at night, and the east, west and north sides are single-slope plastic greenhouses with enclosure walls, which are collectively referred to as solar greenhouses. Its prototype is a single-slope glass greenhouse, and the light-transmitting covering material on the front slope is replaced by a plastic film, which is an early solar greenhouse. The characteristics of solar greenhouses are good heat preservation, low investment and energy saving, which are very suitable for the use of underdeveloped rural areas in my country.

The performance of the solar greenhouse

The light transmittance of energy-saving solar greenhouses is generally above 60%~80%, and the temperature difference between indoor and outdoor can be maintained above 21~25 degrees Celsius.

1. Solar greenhouse lighting

On the one hand, solar radiation is the most important source of energy to maintain the temperature of solar greenhouses or maintain heat balance; on the other hand, solar radiation is the only light source for crops to perform photosynthesis.

2. Solar greenhouse insulation

The thermal insulation of the solar greenhouse consists of two parts: the thermal insulation envelope and the movable thermal insulation quilt. Insulation on the front slope should be flexible material to be easily stowed after sunrise and lowered at sunset.

The research and development of new front roof insulation materials mainly focus on the requirements of easy mechanized operation, low price, light weight, aging resistance, waterproof and other indicators.

The solar greenhouse is mainly composed of three parts: the enclosure wall, the rear roof and the front roof, which are referred to as the "three elements" of the solar greenhouse. The front roof is the entire lighting surface of the greenhouse. When the light is weakened, cover the plastic film with the active thermal insulation quilt in time to strengthen the thermal insulation of the greenhouse.

The solar greenhouse can also be equipped with a top window system, a roll film system, etc.