Advantages And Disadvantages Of Greenhouses

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A greenhouse is a structure with a glass or plastic roof and side walls that is used for the production of ornamentals and food crops and may be used seasonally or year round. The closed environment of a greenhouse has its own unique requirements, compared with outdoor production. Pests and diseases, and extremes of heat and humidity, have to be controlled, and irrigation is necessary to provide water. Significant inputs of heat and light may be required, particularly with winter production of warm-weather crops. (Douglas Cox, ,. 2010)
Consequently covering materials are ones used to cover greenhouse structures that must permit for full light transmission. They can be rigid or flexible, double-walled or single-walled, smooth or corrugated. …show more content…

4. POLYVINYL CHLORIDE (PVC):
This is flexible film that has light transmission qualities similar to glass. This material has been used extensively in Japan. While polyethylene sheets can be wide, PVC is narrow which a disadvantage in covering greenhouses is.
PVC has a number of properties that make it desirable as a covering.
 PVC has excellent resistance to wear.
 PVC film reduces the transmission of long wavelength infrared radiation, resulting in less heat loss at night using PVC as a covering than using polyethylene.
 PVC film is more expensive than PE film, but you can expect it to last up to 5 years. PVC plastic is available with UV protection and you can find PVC that reduces condensation.
 Oxidation has little effect on PVC, but heat and light break down PVC film in 2 to 3 years.
5. ETHYLENE-VINYL ACETATE …show more content…

EVA copolymers are transparent to visible light, and allow all those wavelengths essential for photosynthesis to pass through. In addition, they have good heat retaining characteristics to an extent which depends on the vinyl acetate content.EVA copolymers have good light transmission and thermal characteristics, but some have the defects of being liable to excessive stretching and tackiness. Because these properties are influenced by the vinyl acetate content, the final use for the film will determine the type of EVA copolymer required. Films for greenhouse covers should have good resistance to stretching at high temperatures. Otherwise, on warm, windy days the film will stretch and flap on its supports and this may result in damage to the structure. For greenhouse covers, therefore, the vinyl acetate content should be less than 15%. A long life is also required for films used to cover greenhouses. Special formulations are available with UV stabilizers which give films a life of at least 3

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