All You Need to Know About Greenhouse and Net House Coverings
Orly Shiri - Department of Marketing
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When growing different crops in greenhouses and net houses, the matter of coverings weighs heavily on the success of the yield.  Clearly, each and every grower aspires for maximum production and high quality crops.  Therefore, when constructing a greenhouse, the type of covering must also be taken into consideration.


Among other elements, the film covering influences the overall energetic balance of the greenhouse.  In other words, the transmission of light, the activities of insects and other matters are directly affected by the quality of the covering.


Greenhouse coverings fulfill a number of functions, including: shading the crops, reducing heat burdens, controlling the development of the plants and the maturing of fruit, and preventing the infiltration of insects.


When we talk about "coverings", we are referring to film sheets, panels and netting.


Polyethylene Film Sheets


Polyethylene film sheets are used for covering greenhouses. The sheets are comprised of a number of layers of film, treated with various additives that add qualities to the film for improving internal climate conditions. In addition, these additives increase the durability of the film sheets.


The width of the film used for covering greenhouses ranges from 120 to 33 microns. The use of technological production methods that combine up to five layers of film enables the addition of a strengthening package:  the processing of a variety of raw materials that increase the mechanical strength of the film as well as its transparency and durability, even under difficult climate conditions.


Additives and Additional Qualities of the Polyethylene Film Sheets


IR


The addition of IR enables infrared (IR) light (with a wavelength that ranges between 700-1500 nanometers) to penetrate the thermal film and prevents it from leaving the structure.  In other words, there is directionality (enabling it to enter but preventing it from leaving).  In addition, it prevents the IR that is radiated within the greenhouse from escaping, which helps to reduce the cooling of foliage during the night.


Anti-drip


When the humidity levels inside the greenhouse are very high, drops of water form on the surface of the film.  The water drips down onto the plants and creates conditions that encourage the development of plant disease.  Another cause for the accumulation of water drops on the film is the difference between internal and external temperatures during the night.  The anti-drip qualities added to the film layers cause the drops of water to flatten and slide into the gutters, instead of dripping down onto the foliage.


Anti-virus – Blocking the UV Field


This quality disrupts the activities of insects inside the greenhouse.  For agricultural produce intended for export, in addition to local markets, the awareness of methods that help to reduce the use of pesticides has greatly increased.  These films have been found to be very effective for this purpose.


Diffusion


This quality diffuses light rays equally throughout the greenhouse and helps to ensure more efficient photosynthesis as the various parts of the plant are better exposed to visible rays of light.  In addition, the dispersion of light helps to prevent burning and the formation of sun spots on the leaves of the plants.


Palrig (Reinforced Polyethylene)


Palrig, a type of film made from polymers, is characterized by its great strength.  The film can be used as a ground covering.  Proper covering of the ground significantly reduces the evaporation of water, encourages organic activity by raising ground temperatures and prevents the growth of weeds. In addition, the greenhouse remains clean and maintains an aesthetic appearance when its grounds are covered. Palrig film can also be used as a covering for rooftops, along sidewall windows or sewn to the netting along the sides of the greenhouse to protect plants from the cold and from winds.  The advantages to using Palrig on the rooftops are quite significant. The film is ber and more durable than polyethylene and does not have to be replaced as often.  Palrig film is also treated with additives such as anti-fog, IR and UV blocking.


Polycarbonate Panels


Polycarbonate is a rigid material and due to a number of its qualities, it is one of the best materials to use for covering greenhouses.  In addition to being b and sturdy, polycarbonate maintains its qualities over many years and is highly durable. It can be manufactured to provide up to 95% light transmission and can save up to 50% on energy costs.


Additional qualities of polycarbonate include:  flexible and easy to install; durable over a wide range of temperatures: 50-100° C; capable of bearing very heavy weights and therefore, polycarbonate is ideal for areas in which heavy snowfall and hail are prevalent. The primary disadvantage:  relatively expensive in comparison to other greenhouse coverings, such as polyethylene.


Azrom greenhouses that are covered with polycarbonate have been designed to withstand wind gusts up to 120-180 km/h and have been adapted to bear the most extreme weather conditions, depending on field and client requirements.


Similar to the polyethylene film sheets, polycarbonate panels can also be treated to provide desired qualities, such as:  IR, anti-virus, anti-drip and diffusion.


Netting: Woven and Knitted Nets


Woven Nets:  Woven nets are made from individual wires woven together at varying densities. They are used primarily for protecting against insect infiltration and for shading purposes.


Knitted Nets: Knitted nets are made of wires or strips of plastic film sheets that are processed to the desired thickness and strength and then knitted into netting.  Theses nets are used primarily for shading purposes and for mechanical protection of crops.


The knitted nets provide shading levels ranging from 20% to 90% and come in a variety of colors.


There is a knitted reflective film called "Aluminet" that is available in different shading levels.  This film is used for shading and protection under extreme climate conditions.  Azrom installs this film to serve as a motorized screen that can be moved from one side of the greenhouse to the other (opened or closed).  The grower can spread the film screen quickly and effectively in the early evening hours (during cold spells) and remove it when morning temperatures begin to rise. The film screen can also be used during times of heavy heat burdens within the greenhouse.


Azrom is currently one of the world's leading companies for the production of greenhouses.


Every project, anywhere in the world, receives the proper, individual consideration, combining: local characteristics, design and planning, agronomic consultation, examination of growing conditions, construction and the planning of supplementary units and systems, including electricity, water, heating, trellising, climate control and fertilization.  Only an overall, comprehensive solution, be it simple or complex, is the perfect response.


The company's quality control policy focuses on the supply of qualitative products for long term client use under difficult and challenging field conditions.


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