What is a greenhouse? What is the basic structure of a greenhouse?

Greenhouse generally refers to a protective facility with roof and wall structure, which has good thermal insulation performance and can be used for agricultural production under severe cold conditions.

Commonly used greenhouses are mainly composed of walls, rear roofs, front roofs, columns and heat preservation covers.

(1) Wall includes back wall, east wall and west wall, and is generally composed of soil, grass mud, masonry, etc. Glass greenhouses and hard plastic greenhouses are glass walls or plastic plates. Earth walls are usually made into a "trapezoidal wall" with a narrow top and a wide bottom. General bottom width 1.2 ~ 1.5m and top width1~1.2m.. Masonry walls are generally built into "sandwich walls" or "hollow walls" with a width of about 0.8 meters, and are filled with heat preservation materials such as vermiculite, perlite and slag.

The height of the back wall is 1.5 ~ 3m. The front height of the side wall is about 1 m, and the back height is the same as that of the back wall, and the ridge height is 2.5 ~ 3.8m..

(2) Back Roof The back roof of a common greenhouse is mainly composed of thick wood, straw, grass mud and moisture-proof film. Straw is the main thermal insulation material, generally 20 ~ 40 cm thick. The back roof of masonry greenhouse is mostly composed of reinforced concrete precast columns or steel frames, foam boards, cement boards and thermal insulation materials. The main function of the rear roof is to keep warm and place grass.

(3) The front roof consists of a roof truss and a transparent cover.

(1) roof truss. The main function of roof truss is to shape the front roof, support the membrane and grass. There are two basic shapes: semi-arch circle and inclined plane. Bamboo poles, steel pipes, rigid plastic pipes, garden steel and other building materials are mostly processed into semi-arch round roof trusses, and angle steel, channel steel and other building materials are mostly processed into inclined roof trusses. According to the different structural forms, roof trusses are generally divided into ordinary type and string type.

② Transparent covering. The main function is to heat the greenhouse during the day and keep it warm at night. The main materials used are plastic film, glass and polyester board.

Plastic film is the main transparent covering material at present because of its low cost, easy covering, many kinds of films and large choice. The films used are mainly dark blue PVC drip-free dustproof long-life film and polyethylene multifunctional composite film.

Glass has long service life and good thermal insulation performance, but it has high cost and heavy weight, and has strict requirements on the types, specifications and construction quality of arch frames, so it is rarely used at present.

Polyester board is mainly composed of glass fiber reinforced polyester board (ERP board) and polycarbonate board (PC board). Polyester board has the advantages of light specific gravity, good thermal insulation, high light transmittance, long service life and so on. Generally, it can be used continuously for more than 10 years, which is developing internationally. The polyester board greenhouse in China has also been developed in recent two years.

(4) Columns Generally, there are 3-4 rows of columns in ordinary greenhouses. According to the position of the column in the greenhouse, it is called back column, middle column and front column respectively. The main function of the rear column is to support the rear roof, and the central column and the front column are mainly to support and fix the arch. The columns are mainly precast cement columns, and the section specification is10 ~15cm×10 ~15cm. Generally, the burial depth is 40 ~ 50 cm. The rear column is 0.8 ~ 1.5m away from the rear wall, and is buried underground, with an inclination of about 5 to the north. Most other columns are buried vertically. Steel frame structure greenhouses and pipeline structure greenhouses generally do not set up columns.

(5) The main function of the insulation cover is to keep the temperature in the greenhouse in the low temperature period, mainly including straw mats, paper quilts, non-woven fabrics, wide films, insulation quilts, etc.

(1) grass cover. With low cost and good thermal insulation, it is the most widely used thermal insulation covering material at present. Its main disadvantage is that its service life is relatively short, and the general continuous use time is only about 3 years. In addition, the grass has a large volume, which is not convenient to collect, and it is also easy to get wet by rain and snow, which reduces the thermal insulation performance. There are two main kinds of barnyard grass, namely, barnyard grass and cattail barnyard grass, and the former is widely used. Generally, the thickness of grass used in greenhouse is more than 3 cm, and the width is 1.2 ~ 2 m, depending on the length of the front and rear roofs.

② Paper quilt. Multi-purpose kraft paper splicing. Generally, the paper quilt sewn with four layers of kraft paper can increase the temperature by 3 ~ 5℃, with good thermal insulation effect, small volume, light weight and easy storage. Its main disadvantage is that it is easy to absorb moisture and break after being wet. Paper is mainly used as an auxiliary thermal insulation material, which is combined with straw mats in cold winter areas and covered under straw mats to enhance the thermal insulation effect.

③ Nonwoven fabric. It is a chemical fiber cloth made of polyester filament, polypropylene fiber and other materials. Non-woven fabrics have the advantages of light weight, good air tightness, obvious thermal insulation effect and long service life, and can generally be used continuously for more than 3 years. Its main disadvantage is its high cost. Non-woven fabrics are mainly used as auxiliary thermal insulation materials, which are covered under straw mats in winter and keep the greenhouse temperature together with straw mats. Non-woven fabrics are named after the weight per square meter (grams), and the specifications range from 20 grams to 200 grams. Thick and heavy non-woven fabrics are selected for greenhouse insulation.

④ Wide film. Ordinary polyethylene film with a width of more than 8 meters can also be replaced by the old shed film removed from the shed to reduce the cost. As an auxiliary thermal insulation material for greenhouses, straw mats are usually covered with a wide film, which can not only strengthen the thermal insulation, but also prevent the straw mats from getting wet by rain and snow, and the comprehensive thermal insulation effect is better, generally increasing the temperature by 2 ~ 4℃.

⑤ Insulation quilt. In recent years, a new type of greenhouse insulation covering material has been developed, which is made of multiple layers of materials with different functions. It has a series of advantages, such as long service life, good thermal insulation performance, waterproof, light weight and suitable for automatic mechanical winding. It is a substitute for traditional straw mats, but its popularization is slow at present because of its high cost.