Types greenhouse covers and features their
1- Glass cover
Glass as a greenhouse cover It has high light transmittance, longevity and stability, so that ultraviolet light rays do not affect its stability and longevity, but they are vulnerable to hail and heavy snow, and as time passes and they become dirty, their light transmission decreases. As a result, they must always be kept clean. The thickness of these coatings is between 3 and 5 mm. These glasses do not pass ultraviolet and infrared rays. Among the disadvantages of these coatings, the following can be mentioned:
> High initial cost of the structure, equipment and their installation
> expensiveness of glass compared to other coverings
> higher heating cost of greenhouses Glass
> High probability of breaking glass with hail
2- non-glass covers
These coatings can be divided into two categories: soft plastics
and hard plastics: p>
*covers Soft plastic
– Polyethylene (PE) covers
The initial cost of preparing polyethylene covers is less and can be easily used, and therefore the most use for greenhouse covers. These covers are produced in different widths and 50 meters long.
– two-layer plastic covers with compressed air
One of the ways to reduce heat losses and reduce dripping in greenhouses with soft plastic cover is to use two layers of plastic and a cushion of compressed air between them. With this method, energy consumption is reduced by about 40%. The appropriate thickness for the compressed air layer is about 10 to 15 cm and the appropriate pressure is 0.5 to 1 cm of mercury, which requires a blower and a pressure gauge.
This thermoplastic coating is very soft, flexible and has high toughness, transparency and adhesion.
This cover type have good resistance against cracking and perforation.
It is chemically inert and can be heated, so it is used for Greenhouse cover makes attractive.
These coatings are more resistant to ultraviolet rays and infrared waves than polyethylene.
– Polycarbonate (PC)
Polycarbonate is the hardest transparent material that is suitable as an option
can be used instead of glass in different sections.
These sheets, in addition to a style with impact resistance, abrasion resistance
and are dimensionally stable.Heat exchange of polycarbonate sheets
is also less than plastic and glass, among its advantages
its light weight is similar to glass. The cost of these covers compared to plastic
is more. Their light transmission rate from glass is less and their status against
more climate change.
Acrylic is a lightweight and shatter-resistant polymer and a suitable alternative
is for glass.Acrylic can be used when high strength is not required
considered a cheap alternative to polycarbonate.
Transmission of visible light in acrylic is very high. This plastic
It is very resistant to weather changes and its dimensionality is relatively good.
These coatings do not change color and have good resistance against ultraviolet rays
have.In addition, they are highly flammable and permeable to water vapor
are .
Fiberglass is a type of fiber reinforced polymer in which
Glass fibers are used as reinforcement in two or three dimensions.
background material Reinforced polymers of epoxy resin, vinyl ester, polyester
or any thermoplastic polymer.
Among its features are high tensile strength,
High temperature tolerance, dimensional stability, easy washing, light in these greenhouses
These covers are cheaper than glass and They are more expensive than polyethylene.
Among the disadvantages of these coatings are flammability and reduced light transmission after
several washes and scratches and lack of light transmission
It is due to the accumulation of dust.
