AgriMANIA

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

The type of construction is predominantly influenced by the structural material, though the covering material also influences the type. Span of the house inurn dictates the selection of structural members and their construction. Higher the span, stronger should be the material and more structural members are used to make sturdy truss type frames. For smaller spans, simpler designs like hoops can be followed.   Therefore based on construction, greenhouses can be broadly classified as wooden framed, pipe framed and truss framed structures. Wooden framed structures In general, for the greenhouses with span less than 6 m, only wooden framed structures are used.   Side posts and columns are constructed of wood without the use of a truss. Pine wood is commonly used as it is inexpensive and possesses the required strength.   Timber locally available, with good strength, durability and machinability also can be used for the construction. Figure: Wooden framed structure

Classification of greenhouses can be made depending on the functions or utilities. Of the different utilities, artificial cooling and heating of the greenhouse are more expensive and elaborate. Hence based on the artificial cooling and heating, greenhouses are classified as green houses for active heating and active cooling system. Greenhouses for active heating During the night time, air temperature inside greenhouse decreases. To avoid the cold bite to plants due to freezing, some amount of heat has to be supplied. The requirements for heating greenhouse depend on the rate at which the heat is lost to the outside environment. Various methods are adopted to reduce the heat losses, viz., using double layer polyethylene, thermo pane glasses (Two layers of factory sealed glass with dead air space) or to use heating systems, such as unit heaters, central heat, radiant heat and solar heating system. Greenhouses for active cooling During summer season, it is desirable t

Greenhouse structures of various types are used successfully for crop production. Although there are advantages in each type for a particular application, in general there is no single type greenhouse, which can be considered as the best. Different types of greenhouses are designed to meet the specific needs. GREENHOUSE TYPE BASED ON SHAPE Greenhouses can be classified based on their shape or style.    For the purpose of classification, the uniqueness of the cross section of the greenhouses can be considered as a factor.    As the longitudinal section tend to be approximately the same for all types, the longitudinal section of the greenhouse cannot be used for classification. The cross sections depict the width and height of the structure and the length is perpendicular to the plane of cross section. Also, the cross section provides information on the overall shape of the structural members, such as truss or hoop, which will be repeated on every day. The commonly followed