Module 1. History and types of greenhouse
Module 2.Function and features of greenhouse
Module 3.Scope and development of greenhouse techn...
Module 4.Location, planning and various components...
Module 5.Design criteria and calculations
Module 6. Construction materials and methods of co...
Module 7. Covering material and characteristics
Module 8. Solar heat transfer
Module 9. Solar fraction for greenhouse
Module 10. Steady state analysis of greenhouse
Module No. 11 Greenhouse Heating, Cooling, Sheddin...
Module 12. Carbon dioxide generation and monitorin...
Module 13. Instrumentation and & computerized ...
Module 14. Watering, fertilization, root substrate...
Module 15. Containers and benches
Module 16. Plant nutrition, Alternative cropping s...
Module 17. Plant tissue culture
Module 18. Chemical growth regulation
Module 19. Disease control, integrated pest manage...
Module 20: Post Production Quality and Handling
Module 21: Cost analysis of greenhouse Production
Module 22. Application of greenhouse & its rep...
Lesson 1 History and Types of Greenhouse
What is Greenhouse Technology?
Today about 92% of plants, raised by man, are grown in the open field. Since the beginning of agriculture, farmers have had to cope with the growing conditions given to them by Mother Nature. In some of the temperate regions where the climatic conditions are extremely adverse and no crops can be grown, man has developed technological methods of growing some high value crops by providing protection from the excessive cold and excessive heat. This is called Greenhouse Technology. “Greenhouse Technology is the science of providing favourable environment conditions to the plants”. It also protects the plants from the adverse climatic conditions such as wind, cold, precipitation, excessive radiation, extreme temperature, insects and diseases. An ideal micro climate can be created around the plants. Greenhouses are framed or inflated structures covered with transparent or translucent material large enough to grow crops under partial or full controlled environmental conditions to get optimum growth and productivity.
1.2 HISTORICAL BACKGROUND OF GREENHOUSES
Before the 20th century - Agriculture production inside protected structures was initiated in France and Netherlands in the 19th century. This method was applied in simple, low, glass structures, which provided climate protection, and were used mainly for the growth of ornamental plants.
Modern Times - By the beginning of the 20th century, mostly after the end of 2nd world war, the technology of greenhouse construction accelerated its development, especially in Western Europe cold countries, Netherlands leading the course. Agro-technical systems, aeration solutions and accompanying accessories were gradually added to the structures, while the structure foundations improved to the known, traditional heavy steel constructions covered by rigid glass boards.
New Materials - By the end of the fifties of the 20th century the greenhouses technology flowed to the north and center of Europe, extending its influence and benefits to Israel, where a wave of experiments and research in the field had begun. The sixties revealed a new kind of structure covering sheets. They were the flexible, low priced polyethylene sheets, which caused a conceptual revolution in the field of greenhouses. Simultaneously appeared other types of good light transition coverings, such as polycarbonate (a kind of covering made of plastic polymers) leaving behind the traditional glass covering.
New Technologies - The method of modular structures (Lego-like method) leads to the development of growth technologies suitable for most types of crops, thus creating customized structure projects, customer-tailored according to specific needs. This new trend caused the breakdown of the traditional, conservative Dutch hegemony ruling until then in the field of greenhouses. Nowadays, light-weighted structures with covering made of flexible polyethylene or stiff-flexible polycarbonate are more common and widespread than the mythological rigid glass greenhouses.
1.3 TYPES OF GREENHOUSES
Greenhouse structures of various types are used for crop production. Although there are advantages in each type for a particular application, in general there is no single type of greenhouse, which can be constituted as the best. Different types of greenhouses are designed to meet the specific needs. The different types of greenhouses based on shape, utility, material and construction are briefly given below:
1.3.1. Greenhouse Type Based On Shape:
For the purpose of classification, the uniqueness of cross section of the greenhouses can be considered as a factor. The commonly followed types of greenhouses based on shape are:
Lean to type greenhouse.
Even span type greenhouse.
Uneven span type greenhouse.
Ridge and furrow type.
Saw tooth type.
Interlocking ridges and furrow type Quonset greenhouse.
Ground to ground greenhouse.
22.214.171.124 Lean-to type greenhouse
A lean-to design is used when a greenhouse is placed against the side of an existing building. It is built against a building, using the existing structure for one or more of its sides (Fig.1.3.1). It is usually attached to a house, but may be attached to other buildings. The roof of the building is extended with appropriate greenhouse covering material and the area is properly enclosed. It is typically facing south side. The lean-to type greenhouse is limited to single or double-row plant benches with a total width of 7 to 12 feet. It can be as long as the building it is attached to. It should face the best direction for adequate sun exposure.
The advantages of the lean-to type greenhouse are;
It is usually close to available electricity, water, and heat.
It is a least expensive structure.
This design makes the best use of sunlight and minimizes the requirement of roof supports.
Disadvantages of the lean-to type greenhouse are;
Limited space, limited light, limited ventilation and temperature control.
The height of the supporting wall limits the potential size of the design.
Temperature control is more difficult because the wall that the greenhouse is built on, may collect the sun's heat while the translucent cover of the greenhouse may lose heat rapidly.
Fig. 1.3.1. Lean-to-type type greenhouses
126.96.36.199 Even span type greenhouse
The even-span is the standard type and full-size structure, the two roof slopes are of equal pitch and width (Fig.1.3.2). This design is used for the greenhouse of small size, and it is constructed on level ground. It is attached to a house at one gable end. It can accommodate 2 or 3 rows of plant benches. The cost of an even-span greenhouse is more than the cost of a lean-to type, but it has greater flexibility in design and provides for more plants. Because of its size and greater amount of exposed glass area, the even-span will cost more to heat. The design has a better shape than a lean-to type for air circulation to maintain uniform temperatures during the winter heating season. A separate heating system is necessary unless the structure is very close to a heated building. It will house 2 side benches, 2 walks, and a wide center bench. Several single and multiple span types are available for use in various regions of India. For single span type the span in general, varies from 5 to 9 m, whereas the length is around 24 m. The height varies from 2.5 to 4.3 m.
Fig 1.3.2. Even Span Type Greenhouse
188.8.131.52 Uneven span type greenhouse
This type of greenhouse is constructed on hilly terrain. The roofs are of unequal width; make the structure adaptable to the side slopes of hill (Fig.1.3.3). This type of greenhouses is seldom used now-a-days as it is not adaptable for automation.
Fig 1.3.3. Uneven Span Type Greenhouse
184.108.40.206 Ridge and furrow type greenhouse
Designs of this type use two or more A-frame greenhouses connected to one another along the length of the eave (Fig. 1.3.4). The eave serves as furrow or gutter to carry rain and melted snow away. The side wall is eliminated between the greenhouses, which results in a structure with a single large interior, Consolidation of interior space reduces labour, lowers the cost of automation, improves personal management and reduces fuel consumption as there is less exposed wall area through which heat escapes. The snow loads must be taken into the frame specifications of these greenhouses since the snow cannot slide off the roofs as in case of individual free standing greenhouses, but melts away. In spite of snow loads, ridge and furrow greenhouses are effectively used in northern countries of Europe and in Canada and are well suited to the Indian conditions.
Fig. 1.3.4. Ridge and furrow type greenhouses
(Source: www.nafis.go.ke )
220.127.116.11 Saw tooth type Greenhouse
These are also similar to ridge and furrow type greenhouses except that, there is provision for natural ventilation in this type. Specific natural ventilation flow path (Fig. 5) develops in a saw- tooth type greenhouse.
Fig. 5. Saw tooth type greenhouses
(Source: www.netafim.com )
18.104.22.168 Quonset greenhouse
This is a greenhouse, where the pipe arches or trusses are supported by pipe purling running along the length of the greenhouse (Fig. 1.3.6). In general, the covering material used for this type of greenhouses is polyethylene. Such greenhouses are typically less expensive than the gutter connected greenhouses and are useful when a small isolated cultural area is required. These houses are connected either in free, standing style or arranged in an interlocking ridge and furrow. In the interlocking type, truss members overlap sufficiently to allow a bed of plants to grow between the overlapping portions of adjacent houses. A single large cultural space thus exists for a set of houses in this type, an arrangement that is better adapted to the automation and movement of labour.
Fig. 1.3.6 Quonset Type Greenhouse
(source: www.gothicarchgreenhouses.com )
1.3.2. Greenhouse Type Based on Utility
Classification can be made depending on the functions or utilities. Of the different utilities, artificial cooling and heating are more expensive and elaborate. Hence based on this, they are classified in to two types.
Greenhouses for active heating.
Greenhouses for active cooling.
22.214.171.124 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.
126.96.36.199 Greenhouses for active cooling
During summer season, it is desirable to reduce the temperatures of greenhouse than the ambient temperatures, for effective crop growth. Hence suitable modifications are made in the green house so that large volumes of cooled air is drawn into greenhouse, This type of greenhouse either consists of evaporative cooling pad with fan or fog cooling . This greenhouse is designed in such a way that it permits a roof opening of 40% and in some cases nearly 100%.
1.3.3. Greenhouse Type Based on Construction
The type of construction predominantly is influenced by structural material, though the covering material also influences the type. Higher the span, stronger should be the material and more structural members are used to make sturdy tissues. For smaller spans, simple designs like hoops can be followed. So based on construction, greenhouses can be classified as
Wooden framed structure.
Pipe framed structure.
Truss framed structure.
188.8.131.52 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 (Fig1.3.7) Pine wood 8 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.
Fig 1.3.7. Wooden Framed Greenhouses
(Source:www.mcgreenhouses.com, www.greenhouseandsunrooms.com )
184.108.40.206 Pipe framed structures
Pipes are used for construction of greenhouses, when the clear span is around 12m (Fig. 1.3.8). In general, the side posts, columns, cross ties and purlins are constructed using pipes. In this type, the trusses are not used.
Fig1.3.8. Pipe Framed Greenhouse Structures
220.127.116.11 Truss framed structures
If the greenhouse span is greater than or equal to 15m, truss frames are used. Flat steel, tubular steel or angular iron is welded together to form a truss encompassing rafters, chords and struts (Fig. 1.3.9). Struts are support members under compression and chords are support members under tension. Angle iron purlins running throughout the length of greenhouse are bolted to each truss. Columns are used only in very wide truss frame houses of 21.3 m or more. Most of the glass houses are of truss frame type, as these frames are best suited for pre-fabrication.
Fig 1.3. 9. Truss Framed Greenhouse Structures
1.3.4. Greenhouse Type Based on Covering Material
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.
1.3. 4.1 Glass greenhouses
Only glass greenhouses with glass as the covering material existed prior to 1950. Glass as covering material (Fig.1.3.10) 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.
Fig.1.3.10 Glass Greenhouse
18.104.22.168 Plastic film greenhouses
Flexible plastic films including polyethylene (Fig. 1.3.11), 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.
Fig.1.3.11 Polyethylene film greenhouse
(Source: www.poly-ag.com )
22.214.171.124 Rigid panel greenhouses
Polyvinyl chloride rigid panels, fibre glass-reinforced plastic, acrylic and polycarbonate rigid panels (Fig.1.3.12) 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 harbor algae, which results in darkening of the panels and subsequent reduction in the light transmission. There is significant danger of fire hazard.
Fig.1.3.12 Polycarbonate Covering
(Source: www.advancegreenhouses.com )
1.3.5 Greenhouse Type Based on Cost of Construction
Based on the cost of construction involved;
High cost Green House
Medium cost Green House
Low cost Green House
1.3.6 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 fulfil 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 fulfil 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 (fig 1.3.13) is available in the market which is defined on the basis of the percentage of shade they deliver to the plant growing under them.
Fig 1.3.13 Shading net
(Source: www.chinaplasticmesh.com )