1. Classification of sunshade for multi-span greenhouses
Multi-span greenhouses are divided into two types according to the installation location: external sunshade system and internal sunshade system. The external sunshade net is generally fixed by a steel frame connected by external sunshade columns and horizontal and vertical beams. The external sunshade net generally uses round wire black net, which is more sun-resistant and directly blocks the light outside our greenhouse.
The other is the internal sunshade system. The internal sunshade is a sunshade net fixed on the beam of the multi-span greenhouse. The most commonly used ones are aluminum foil nets and pure white nets. The internal sunshade net plays the role of sunshade and scattering.
2. Introduction to internal and external sunshade systems and principles
The curtain systems used for sunshade and cooling are mainly external sunshade and internal sunshade. External sunshade is installed on the outside of the greenhouse, which can fundamentally reduce the solar radiation heat and sunlight entering the greenhouse, and has the best sunshade and cooling effect.
Internal sunshade is installed inside the greenhouse, mainly used in conjunction with external sunshade to prevent strong light from burning plants. It cannot achieve a cooling effect when used alone, but can be used for heat preservation at night. From the material of the curtain, the common sunshade curtains mainly include black knitted sunshade curtains, aluminum foil sunshade curtains and black and white double-sided sunshade curtains. Guangyuan Greenhouse's black knitted sunshade curtains are widely used as external sunshade curtains in my country. They are economical, lightweight and durable, but their shading rate is inaccurate, and the shading and cooling effect is poor under strong solar radiation.
The aluminum foil reflective sunshade curtain is made of braided wires to weave aluminum foil strips into an open-hole structure, which can reflect unnecessary solar radiation and significantly reduce the indoor temperature. Due to the good thermal radiation reflection characteristics of aluminum foil, this type of sunshade curtain is more used for internal sunshade and thermal insulation curtains, which have the dual functions of daytime shading and nighttime insulation.
The black and white double-sided sunshade curtain is woven with braided wires and polyolefin film with white upper surface and black lower surface. It is used for external shading systems. The white upper surface reflects light and heat, which can effectively reduce the thermal radiation entering the greenhouse; the black lower surface blocks excess light and transmits some effective light. This type of sunshade curtain is used in multi-span greenhouses in Yulin, Guangxi, where solar radiation is strong, and has a good shading and cooling effect.
