The types of multi-span greenhouses on the market are classified differently according to different covering materials, and are also different from single-span greenhouses. The details are as follows:
1. Sawtooth multi-span greenhouse
Greenhouses with vertical vents on the roof are collectively called Sawtooth greenhouses. Sawtooth greenhouses can be divided into half-arch and full-arch. The roofing materials are mostly made of plastic film or PC board. This kind of greenhouse has larger vents than the round-arch greenhouse, so the ventilation effect is better. However, the insulation effect is average and when building a Sawtooth greenhouse, special attention should be paid to the local wind direction.
2. Round arched multi-span greenhouse
The dome-shaped multi-span greenhouse adopts a semicircular or reasonable curved skeleton form as the roof structure. It is the most commonly used building shape for plastic film greenhouses. It can also be used for PC board greenhouses. Its structure is simple, the stress is clear, the roof slope is gentle, and the opening The window position is flexible and the cost is low. In the south, single-layer films are mostly used to increase light transmittance. In the north, in order to reduce energy consumption in winter, single-layer plastic films are changed to double-layer plastic films.
3. Venlo greenhouse
The Venlo type greenhouse is a small-roofed double-slope greenhouse. It splits the roof of the ridge-type greenhouse into 2 to 4 small roofs of 3.2 (or 4m) m each span, which reduces the roof height and thus reduces the wind Effect of load. The roof frame is an aluminum alloy profile, and the covering material is mostly made of glass or PC boards. The Venlo-type greenhouse components have small cross-sections, resulting in higher light transmittance of this type of greenhouse. In addition, it has a long service life, strong environmental control capabilities, and large operating space. Large, it is currently the most widely used large-space multi-span glass greenhouse in the world.
Multi-span greenhouses have many advantages over single-span greenhouses, so the construction area of multi-span greenhouses is getting larger and larger. Here are the main advantages and disadvantages of a multi-span greenhouse.
Advantages:
Better control of the environment. As the air volume of a multi-span greenhouse increases, the fluctuations in indoor temperature will decrease. The ratio of the enclosure surface area to the ground area of a small greenhouse is large, and the enclosure surface is the main way for the greenhouse to gain or lose heat, so the air temperature changes quickly.
Heating costs are lower. Because the ratio of the enclosure surface area to the ground area is smaller, the heat loss is smaller. Moreover, the entire multi-span greenhouse space only needs to be equipped with one heating system.
The land utilization rate is higher. The waste of land caused by the spacing between single-span greenhouses is overcome in multi-span greenhouses.
The internal space is more fully utilized. In single-span greenhouses such as Quonset, the side walls are curved sloping walls, and the ground is not fully utilized. This problem does not exist with multi-span greenhouses.
Easy to expand. An attached greenhouse extension is easily attached to an existing greenhouse by adding a few rows of gutter posts. Existing gables or side walls can be removed completely or retained for use as greenhouse partitions.
Flexible partitioning. Partition walls can be installed in multi-span greenhouses to carry out zoning management in the greenhouse.
Disadvantages of multi-span greenhouses:
1. Single plant area. Without partition walls, the greenhouse would become a single growing area, limiting the possibility of growing multiple plants at the same time.
2. The initial investment is high.
3. Plant diseases and insect pests spread easily. Lack of physical barriers to prevent pests and diseases.
4. Uneven areas of hot and cold may occur. Multi-span greenhouses have a large area and are prone to ventilation dead spots, especially when circulating fans are not used. This phenomenon is more obvious.
5. The gutters may be covered with snow. Although snow in greenhouse gutters will melt when heated, it is still necessary to monitor the snow accumulation in the gutters to avoid structural damage.
Multi-span greenhouses have improved the degree of automation. Arm-type sprinkler irrigation systems, hanging basket cultivation systems, hot water heating pipes and sunshade systems can be installed in the multi-span greenhouse space.
Saves more manual labor. In multi-span greenhouses, workers do not have to go back and forth to each greenhouse to perform production operations like they do in single-span greenhouses. In addition, multi-span greenhouses make it easier to use equipment such as forklifts, carts, and monorail transportation to reduce the amount of manual labor.
Multi-span greenhouses can prevent crops from being exposed to the cold outdoor air in winter during operation. Some multi-span greenhouses can also be built very tall to meet the space requirements for loading large trailers of animals.
