GREENHOUSE TYPE BASED ON COVERING MATERIALS

Covering  materials  are  the  major  and  important  component  of  the  greenhouse  structure. Covering materials have direct influence on the greenhouse effect inside the structure and they alter the air temperature inside the house. The types of frames and method of fixing also varies with the covering material.   Based on the type of covering materials, the greenhouses are classified as glass, plastic film and rigid panel greenhouses.

Glass greenhouses

Only glass greenhouses with glass as the covering material existed prior to 1950.  Glass as covering material has the advantage of greater interior light intensity.   These greenhouses have higher air infiltration rate which leads to lower interior humidity and better disease prevention.  Lean-to type, even span, ridge and furrow type of designs are used for construction of glass greenhouse.

Figure: Glass greenhouse

Plastic film greenhouses

Flexible plastic films including polyethylene, polyester and polyvinyl chloride are used as covering material in this type of greenhouses.  Plastics as covering material for greenhouses have become popular, as they are cheap and the cost of heating is less when compared to glass greenhouses. The main disadvantage with plastic films is its short life.  For example, the best quality ultraviolet (UV) stabilized film can last for four years only.  Quonset design as well as gutter-connected design is suitable for using this covering material.

Figure: Plastic film greenhouse

Rigid panel greenhouses

Polyvinyl chloride rigid panels, fibre glass-reinforced plastic, acrylic and polycarbonate rigid panels are employed as the covering material in the quonset type frames or ridge and furrow type frame. This material is more resistant to breakage and the light intensity is uniform throughout the greenhouse when compared to glass or plastic. High grade panels have long life even up to 20 years. The main disadvantage is that these panels tend to collect dust as well as to 5  harbor algae, which results in darkening of the panels and subsequent reduction in the light transmission. There is significant danger of fire hazard.

Figure: Rigid panel greenhouse

Shading nets

There are a great number of types and varieties of plants that grow naturally in the most diverse climate conditions that have been transferred by modern agriculture from their natural habitats to controlled crop conditions. Therefore, conditions similar to the natural ones must be created for each type and variety of plant. Each type of cultivated plant must be given the specific type of shade required for the diverse phases of its development. The shading nets fulfill the task of giving appropriate micro-climate conditions to the plants.

Shade nettings are designed to protect the crops and plants from UV radiation, but they also provide protection from climate conditions, such as temperature variation, intensive rain and winds. Better growth conditions can be achieved for the crop due to the controlled micro-climate conditions “created” in the covered area, with shade netting, which results in higher crop yields. All nettings are UV stabilized to fulfill expected lifetime at the area of exposure. They are characterized of high tear resistance, low weight for easy and quick installation with a 30-90% shade value range. A wide range of shading nets are available in the market which are defined on the basis of the percentage of shade they deliver to the plant growing under them.