Plastic green house

Plastic green house

INTRODUCTION
A greenhouse is a framed or inflated structure covered with glass or plastic where crops could be grown under at least partially controlled environment and which is large enough permit a person to enter into it and carry out cultural operations. Because of considerably lower initial investment, almost all new commercial greenhouse constructions utilize plastics as the glazing material. Green house have a horticultural crops, including rare and medicinal plants, especially under adverse agro-climatic conditions. Greenhouses permit round the year cultivation.

SITE SELECTION AND ORIENTATION OF GREENHOUSE :

A good site can make a difference in the functional and environmental operations of greenhouse. Ground slope for drainage is an important factor. Adequate provision should be made to divert surface water away from the greenhouse.
A greenhouse needs a dependable source of energy in the form of electricity and/or other fuel for environmental control. An electric power distribution line adjacent to the site will reduce the investment on cable laying A short access to all weather public road will facilitate material handling to and from greenhouse. Nearness supply to the market is another added advantage. A dependable supply of good quality water is needed for a greenhouse. Greenhouses should be located away from buildings and trees to avoid obstruction of sunlight.
Orientation of the greenhouse is another important factor. An East-West oriented free standing greenhouse maintains better winter light as compared to a North-South oriented greenhouse. Therefore, in north India, a free standing greenhouse should be oriented in East-West direction.. Gutter connected greenhouses should be oriented North-South to avoid continuous shading of certain portions of the green house due to structural members.
A greenhouse structure has three distinct segments i.e. frame, glazing material and control/monitoring equipment. All the three components have different designed life periods Whereas a greenhouse frame is designed for a service period of 15 to 25 years, glazing materials have lire span or 2 to 20 years, control and monitoring equipment normally wear out in 5 to 10 years.
In the prevailing economic conditions, where capital is a scare input, the choice often favors low initial investment greenhouses. Galvanised mild steel pipe as a structural member in association with wide width u.v.stabilized polyethylene film is a common option selected by greenhouse designers. A 600 to 800 gauge thick polyethylene film can safely withstand normal wind loads prevailing in most parts of the country. A single piece polyethelene film to cover greenhouse is preferred due to material economy, easy handling and improved environmental control. A 800 gauge thick polyethylene film costs approximately Rs.26/square meter and has a service span of 2 to 3 years. The selection of greenhouse equipment depends on local climatic conditions and the crops to be grown. A heating unit is a must in cold regions and a cooling unit is required in all climates in India.
Glass had been used as the sole glazing material till plastics came into existence. Glass has excellent light transmittance and weather resistance but has the disadvantages of brittleness, high cost and heavy weight. Polyethylene and poly vinyl chloride (pvc) films are in use as greenhouse covers. Polyethylene has high light transmittance but lacks durability. U.V. stabilized polyethylene film available in 100 to 250 micron thickness and width of 7m, will last two to three years, depending on quality and local climate. PVC is available as a film or as a rigid panel. PVC with an ultraviolet inhibitor has a life span of 4 years. It is available in 200 to 800 micron thickness and width upto 120 cm. Fibre reinforced plastic (FRP) panels are easy to apply. The problem or discoloration with resulting loss in light transmission and high initial cost have limited their use. They are available upto 120 cm width. Structural panels of double wall glass or rigid plastics are generally used as an energy conservation measure.
The greenhouse frame is the most important component of a greenhouse system. lt provides support for glazing material and a place for fitting of environmental control equipment. Commonly used structural shapes are gable, quonset and gothic arch with minor changes to suit local conditions. Greenhouse frames are designed to withstand wind, snow and crop "loads with minimum obstruction to sun light. Wind and snowfall data are available from the Meteorology department for every part of India. Crop load occurs due to the need to support the plants by using the greenhouse frame. For most of the locations a frame designed to withstand 100 kmph wind speed, is sufficient with the option to use heavier sections in regions of exceptionally high wind speeds.
Tubular steel sections are the most preferred structural members for greenhouse frames. Wood and aluminium are other common materials. Steel pipes provide required strength at a competitive price and also an assured service life of over 20 years.
To meet the demand for construction of low cost greenhouses a tubular frame structure covering the floor area of 4m x 20 m has been developed. Details for construction of the developed greenhouse are given as follows:

STRUCTURAL DETAILS :

The structural members of greenhouse are hoops, foundation, lateral supports, polygrip assembly and end frame. End frames are made of wood and other members are made of galvanised steel.The fabrication details the components have been described below :

HOOPS :

Hoops are the integral part of the greenhouse frame. They are semicircular in shape. Hoops are formed by bending galvanized iron pipe (15 mm dia and 5.9 m length) in a semi-circular shape. For bending of pipes a pipe bender as shown in figure 1 is used. This pipe bender can form pipe in any desired radius. Commercially available 5.9 m (20 ft approx) long pipe is fed by hand into the bender. By rotation of the pulley fitted with a handle uniform bending of pipe is obtained. The central pulley of the pipe bender can be adjusted in such a way that one pass is sufficient to give desired curvature (2 m radius) to the pipe. About 30 cm length on each end remains unbent which enables the ends to easily fit into the foundation pieces

FOUNDATION PIPE

Foundation pipes are meant to provide a firm support to the hoops and to secure the poly grip firmly. Galvanised iron pipes of 25 mm diameter(class A ) and 85 cm length are used as foundation pieces. A 10 cm piece of MS flat (25 x 3 mm) is centrally welded to the one end of pipe and a hole of 8 mm dia is drilled at 10 cm distance from the other end. The flat welded end is put in the dug hole to a depth of 70 cm grouting with concrete as per drawing. A 15 cm length of pipe remains above ground level to hold hoops and polygrip assembly. The foundation pipes are spaced 1.25 m apart in parallel rows. It is important that the tops of these foundation pipes all be at same elevation.

END FRAME

End frames are wooden structures to be fitted on both ends of the greenhouse. The end frame structures are made from 5 cm x 5 cm wooden section. The end frame should have provision for a door and installation of environmental control equipment. ln a smaller size greenhouse (less than 50 square meters of floor) a door is required only on one side while the medium and large size greenhouses may have doors on both ends. The door frame (60 cm x 170 cm) is fabricated from 5 cm x 5 cm wood sections. The open area is covered with either polyethylene film or any other rigid plastic, which is secured to the door frame with wooden battens and nails. The doors, so constructed, are hinged enhance the to the end frames.

LATERAL SUPPORTS

Lateral supports are provided to enhanced the structural rigidity of end frames. These are fabricated from 10 mm dia MS rod. A ring of 3.5 cm dia is made at one end, and a right angle hook on the other. During assembly the ring end encircles the foundation pipe which is put on before putting up hoops. The other end of the lateral support is hooked to the end frame. Four lateral supports are provided at the four corners.

POLY GRIP ASSEMBLY

The polyethylene covering of the greenhouse is to be firmed secured to the foundation pipes, so that it can withstand wind load,. without being blownoff. The polygrip mechanism has been designed in such a way that while it holds polyethylene firmly, puncturing avoided. The polygrip mechanism is made from 20 gauge GI sheet. Two strips of 4 cm and 13 cm width are cut from GI sheet. The 4 cm strip is bent centrally to form a right angle section. The 13 cm strip is bent in the shape of a channel with its edges rounded as shown in the drawing. MS rod of 6 mm dia and 56 mm long pieces are used for positioning channel, angle and polyethylene sandwiched in between and keeping these under pressure. The polyethylene film is stretched and these MS rod pieces are put at a distance of 50 cm, holding the right angle strip against the channel along the whole length of the greenhouse on both sides.

PLASTIC FILM

Ultra violet stabilized polyethylene film of 150 micron to 200 micron thickness is recommended for use in greenhouse glazing. The desured width is 7 m. the film is secured to both sides along the length using the polygrip mechanism and to end frames with wooden nailer. Note Note that a wooden fastening system can be sustituted for the polygrip assembly described above.

RIDGE LINE MECHANISM

In order to keep the hoops at equidistance and increase structural rigidity of the greenhouse structure, the hoops are inter connected with a ridge member. The ridge mechanism for equally spaced hoops is a 15 mm dia GI pipe fastened at the ridge line of the hoops. This ridge line longitudinal pipe is firmly secured to the hoops by the ridge line line grip mechanism which is fabricated from MS
Strapping looped over the crossing of the ridge and hoop and tightened with a bolt as shown in the drawing.

PROCEDURE OF ERECTING THE LOW COST
GREENHOUSE IN THE FIELD

1. A 4 m x 20 m rectangle is marked on the site, preferably orienting the longer dimension in East-West direction. This rectangle wil act as the floor plan of the greenhouse. Make sure that the two diagonals of the rectangle are equal.

2. Mark four points on the four corners of the rectangle. Start from one corner point and move along the length of the marked rectangle, marking a point every 1 25 metre distance until reaching the other corner. The same procedure is repeated on the other side of the rectangle.

3. Dig 10 cm diameter holes to 70 cm depth on all marked points with the help of bucket auger and a crow bar. This way you will get a total of 34 holes on both the parallel sides of the greenhouse floor.

4. Splice polygrip sections formed according to the drawing into two 20 m lengths. Fix the premade polygrip channels to the foundation pipes on 1.25 m spacing with the help of 6 mm dia. bolts. Set these assemblies on temporary supports between the holes with the foundation pipes hanging vertically in the holes and the tops straight and at constant elevation.

5. Pour cement-concrete mixture (1:3:6) around foundation pipes such that the lower 15 cm -20 cm pipe ends are covered in concrete. The concrete is compacted around foundation pipes with the help of the crow bar and is allowed to cure for 2-3 days.

6. After fill soil around the foundation pipes to the ground level and compact it well.

7. Position end frames on the two ends. Mark position of legs. Dig holes for the fixing of legs. Now install both the end frames vertically and duly compact soil on the legs. 8. Put the ring side of support members on adjacent foundation pipe to the corner, and other side is hooked to the end frame.

8. Put all the hoops in the foundation pipes such that the straight portion of hoop is inserted into the foundation pipe and resets on the bolt used for fixing of the polygrip channel.

9. Make a 20 m long ridge pipe by splicing 15 mm pipes together.

10. Put the 20 m long pipe at the ridge line of the hoops. Use cross-connectors on the ridge line pipe such that one half of it remains on the one side of the hoop and the other half on the other side. Put two bolts of 6 mm dia in the holes provided in the ends of the cross connectors and bring the other side closer to it. Now the bolt will pass through the hole of the other half of the cross connector. Tie a few of them with the help of nuts. Repeat the same procedure for joining all the hoops with ridge line pipe. While fixing cross connectors the distance between the hoops/ cross connectors should be maintained 1.25 m (center to center). This grip mechanism will provide a firm grip of the ridge line pipe nd hoops at right angle without allowing for slippage.

11. Spread polyethylene film over the structure from one end to the other without wrinkles and keeping the edges together.

12. Place polyethylene film between the polygrip channel and right angle strip and secure them under pressure with the help of iron rods as shown in the drawing. The film is stretched gently and fixed on the other parallel side by polygrip. This way the polyethylene is secured on both the longer sides.

13. On the other two remaining ends, polyethylene is nailed to the end frames using wooden battens and nails.

14. The remaining portion of the end frames is covered with polyethylene film which is secured with wooden battens and nails. lf fiberglass or other transparent rigid material can be obtained it can be usedon the ends.

15. Mechanical ventilation, Heating and / or cooling equipment is installed on the frames as per the crop requirements (optional).

Bill of material
Galvanised Iron Pipe Construction
4 m x 20 m floor
S.No. Item Specification Quantity

1. G.I. Pipe 15 mm bore, class B 21 pcs, 6 m long
2. G.I. Pipe 25 mm bore, class A 30 m
3. G.I. Sheet 20 guae, 90 cm x 24 cm 4 sheets
4. M.S. Flat 25 mm x 3 mm 4 m (2.5 kg)
5. Nuts, Bolts 6 mm dia, 35 mm long 70 sets
6. Lateral support to end frames 10 mm dia rod 10 m
7. Cement Concrete 1:3:6 1.0 cub. m.
8. Polythylene (Single layer) UV stabilized (800 guage) 154 sq. m. (5.4 sq.m./kg)
9. Miscellaneous (nails, hinges, latches etc.)
10. End frames 5 cm x 5 cm wooden 0.15 cub m wood

(Environmental control equipment as per the local climatic conditions)

Posted in: Agriculture