eChapters

Greenhouses should provide a controlled environment for plant production with sufficient sunlight, temperature and humidity. Greenhouses need exposure to maximum light, particularly in the morning hours. Consider the location of existing trees and buildings when choosing your greenhouse site. Water, fuel and electricity make environmental controls possible that are essential for favourable results. For this reason, use reliable heating, cooling and ventilation.

The greenhouse temperature requirements depend upon which plants are to be grown. Most plants require day temperatures of 70 to 80 degrees F, with night temperatures somewhat lower. Relative humidity may also require some control, depending on the plants cultured. Some plants grow best in cool greenhouses with night temperatures of 50 degrees F after they are transplanted from the seeding tray. These plants include azalea, daisy, carnation, aster, beet, calendula, camellia, carrot, cineraria, cyclamen, cymbidium orchid, lettuce, pansy, parsley, primrose, radish, snapdragon, sweet pea and many bedding plants. Some plants grow best in warm greenhouses with night temperatures of 65 degrees F. These plants include rose, tomato, poinsettia, lily, hyacinth, cattleya orchid, gloxinia, geranium, gardenia, daffodil, chrysanthemum, coleus, Christmas cactus, calla, caladium, begonia, African violet, amaryllis and tulip. Tropical plants usually grow best in high humidity with night temperatures of 70 degrees F.

Specifications

These structures are generally used for the storing grain in the bags. The length of the structure is about twice the width or greater than that. Special care should be taken to make the side walls, floor and roof in constructing the structure. The walls are made of bricks or stones laid either in lime mortar (1:2) or cement mortar (1:6). The thickness is restricted to a minimum of 37.5 cm or maximum of 45 cm. The height of the walls on which the trusses are placed is kept about 5.5 m. Each of the structures is provided with two large size doors of 2.4 × 2.4 m and top ventilators.

Aim

To design a belt conveying system

Theory

The design of belt conveying system is based on available space, horizontal conveying length, conveying lift, characteristics of the materials to be conveyed and capacity requirement.

On the basis of overall requirement and information, the belt width, belt speed, required horsepower, maximum belt tension and breaking strength of the belt, diameter of the pulleys and idlers and quantity of belt (thickness) are determined to design a belt conveyor (Fig.32.1).

Aim

To design bench terrace

1. Components of bench terrace

The bench terrace essentially consists of the four components namely: riser, outlet channel, platform and shoulder bund

Aim

To design a bucket elevator

Theory

The bucket elevator’s capacity mainly depends on bucket size, conveying speed, bucket design and spacing, the way of loading and unloading, the bucket and the characteristic of bulk material.

Bucket elevators with a belt carrier can be used at fairly speeds of 2.5 to 4 m/s. The speed of the belt depends on the head pulley.

If the belt speed is too low, the discharge of the grains become more difficult, with too high speed the buckets are not fed well.

1.0 General

 The design of canal involves following three major aspects:

 A Irrigation and drainage canal network planning.

 B Determination of discharge / capacities of  canals and drainages.

 C Determination of shape and size i.e. geometrical dimensions of the proposed canal section, generally

 known as design of canal section. More appropriately it can be called as design of internal section

 of canal. It can be further divided in three following parts viz.

 i. Design of unlined canals:

 ii. Design of lined canals: or a canal may be partly lined and partly unlined.

 iii. Choice between the unlined and lined canals. This aspect should be distinguished from the selection of type of lining. However, the scope of choice of lining may include both the aspects.

 The design of canal section remains incomplete without the design of its embankments, either in lined or unlined canal, so the next aspect is

 iv. Design of canal embankments. Still to complete the design of a canal one more aspect is required i.e.

 v. Canal aesthetics and canal arboriculture.

Aim

• To design the contour bunds

Design parameters

The design of contour bund includes determination of following parameters:

• Choice of bund
• Spacing of bunds
• Size of bund
• Alignment of bund

1. Choice of bund

The choice of bund should be selected weather the contour bund or graded bund depends on the annual rainfall, soil condition and types of outlets used.

Designing an earthen dam requires the coordinated evaluation of catchment runoff, reservoir capacity, site conditions, foundation properties, expected service life, and the consequences of failure. A selected return period is used to estimate extreme rainfall and runoff, while adequate spillway capacity and freeboard protect the embankment against overtopping. The dam must possess low permeability, stable upstream and downstream slopes, and sufficient resistance to seepage, settlement, erosion, and earthquake forces. This chapter presents design criteria, top width, dam height, side slopes, freeboard, seepage-control components, slope-protection measures, and stability considerations. It also explains procedures needed to create a safe, economical, and functional embankment.

Aim

To design a graded bunds

The procedure in design of contour bund is followed while design a graded bund. A stability of 10-25%, should be given to contour bund. This is called graded bund.

Example: Design a graded bund length of 500 m with an average land slope of 3.5% in a sandy loam soil. Vertical distance between consecutive bund is 2.5 m. Rainfall intensity for the time of concentration and for the recurrence interval is 18.5 cm/hr. The runoff coefficient is 0.3. For stability, the grade provided for first 100 m is 0.1%, for next 200 m is 0.15% and for last 200 m is 0.18%. For the sandy loam soil, side slope of the bund and slope of seepage line are 1.5:1 and 5:1 respectively is assumed.

Aim

To design the grassed water ways or open channel

Geometric characteristics of different waterways

The shape of open channel is dependent upon the field conditions and types of the construction equipments used.

The common shapes of open channels generally used are (i) Parabolic or semi circular (ii) Triangular (iii) Rectangular and (iv) Trapezoidal section.

The parabolic shape approximates a natural channel. The reason is that in natural course of channel flow, the trapezoidal and triangular sections tend to become in parabolic shape due to deposition of sediments and bank erosion.

Aim

To design of greenhouse cooling system

To determine the rate of air exchange in an active summer and winter cooling system.

Theory

Elevation factor (F_elev)

Elevation factor is directly proportional to the elevation. The values of elevation factors, used to correct the rate of air removal for a particular elevation. The rate of air removal from the greenhouse increase as the elevation of the greenhouse site increases.

Theory

Heat required for heating greenhouses is based on the quantity of heat lost through different structural components of greenhouses per unit time. Shapes of greenhouse (A-frame and quonset) and structural components (roof, wall, gable, curtain wall, curved covering and end) are mainly influencing the calculation of heat requirement. The amount of heat lost from a greenhouse depends on glazing materials, exposed surface area of the house, inside desired temperature, outside existing temperature, wind speed, and condition of house (old, new, tight or loose). The outside temperature should be based on the lowest average expected temperature during the heating season.

4.1 Introduction

Experts predict that the global population will exceed 9.6 billion by 2050. This, coupled with the rise of urbanization, the scarcity of arable land, and the destructive effects of climate change, poses significant challenges for agriculture and food production worldwide. To combat these challenges, new horticultural research techniques must be implemented to enhance productivity and efficiency, improve nutrition, and ensure food security, especially during times of crisis like the COVID-19 pandemic. Greenhouse technology has made remarkable strides in recent years, allowing for the manipulation of internal growth elements like temperature, light intensity, and CO2 concentration to create optimal growing conditions

5.1 Irrigation Channels
Canal or channel is an artificially made conduit through which water is supplied to the field from river, tank, reservoir or wells. The open channel is the most common type of water conveyance system. If the pipes and drains are partially full behave like open channel. The irrigation channel may be lined or unlined and the flow is either uniform or varied.

The canal may be classified in following ways.

a) Classification based on the source of supply i) Permanent or perennial canal ii) Inundation canal

A canal is said to be permanent when it is fed by a permanent source of supply and has permanent networks of distribution of supplies. Inundation canals draw their supplies from river usually when water stage exceeds a predetermined level. Headworks are not provided for diversion of river water to canal. However, canal head regulators are provided to regulate the canal head as required time to time to accommodate the changing pattern of river course.

A canal of approximate discharge of less than 80 cumecs (3000 cusecs) discharge may be called a medium or low capacity canal).

3.1 Mehboob Section

A Mehboob Section is only a modification of best trapezoidal section by making its complete bottom circular as shown in figure 3.1. Also see figure 1.6 and para 1.7. That is why these canals are also known as canals of zero bed width, or trapezoidal canals with curved bottom, or cup shaped canals.

But these cannot be called as triangular canals with curves, as often spoken. In fact it is a truncated triangle circumscribing the semi circle. Trapezium is also a truncated triangle circum scribing a circle.

More accurately it can be said as a combination of semi circular and best trapezoidal section so as to take full advantage of their hydraulic efficiency and practicability.

This is such a beautiful section that the designer can never commit a mistake, even if he wants to commit a mistake. The dimensions are so geometrically fixed that no one can play with any dimension.

The value of this section was realised for the first time by Er S I Mehboob (1943) in his Punjab Irrigation Branch Paper No.260" Lining of Canals". There after this canal section became well known as Mehboob Section after his name. He also stated that the most economical section i.e. the maximum area for the minimum perimeter is when the centre of the arc is at the full supply line of the section. This is also evident in figure 1.6. This is also the condition for all best hydraulic sections. This section is also useful to a higher silt carrying capacity than a wide shallow one..

A. Rectangular Canals

5.1 Design of Best Rectangular Canals

After the Mehboob and Trapezoidal canals, next best section is rectangle. This section is also generally adopted for small discharges say upto 10 cumecs (350 cusecs). This section ranks at No. 4. Yet, this is the only section most commonly adopted for flumes of discharges upto140 cumecs (5000 cusecs). Typical example is Orsang acqueduct, 1 km. long for 1140 cumecs (40000 cusecs) in ractangular sections on Narmada Canal Project, Gujrat, India, built in the years from 1990 – 2000. Such sections are common in power house canals due to limitation of space and very sharp curves. It is free from the effect of change of side slopes as in the trapezoidal canals (see para 3.3) Still some small side slope (batter) is adopted in thick masonry / concrete lining. It adds to structural stability with economy in thickness of wall and as well as hydraulic efficiency. It may still be called as rectangular section.

Details of its hydraulic efficiency in comparison to semi circle, Mehboob and trapeziodal sections are discussed in chapter 1, para 1.8

The pipe network in a drip system consists of a mainline, sub mains, laterals, and distributors. The layout of the pipes depends on the physical factors like shape and size of the area, topography and any other obstacles in the field. In any field there may be the scope of different layout of the pipes. The most economic one should be selected. In general, contour line is followed in laying the laterals in sloping land, sub main length usually be shorten in uphill and equally spaced laterals on either side of a sub main in a flat land provides good layout.

Hydraulic Formulae /Head Losses in Pipes

There are numerous equations for solving the head loss in pipes. The most commonly used are the Darcy-Weisbach, Hazen-William and Scobey’s.

P rotected cultivation technology envisages immense promise, especially for high-value crops against various biotic and abiotic stresses. The climatic parameters stress conditions like unusually low and high temperature, humidity, solar radiation, wind velocity comes under abiotic stresses. The present climate change scenario dealing with various biotic and abiotic stress conditions poses serious threat to agricultural production throughout the world. It is estimated that due to one-degree rise in temperature during rabi season, wheat production declines by 4-5 million tonnes in India. Similarly due to prevailing low temperature and frost like conditions, especially in Northern India, several million tonnes of horticultural crops like tomato, brinjal etc. got wasted every year. Protected cultivation technology deals with following types of protected structures :

Aim

To design a screw conveyor

Theory

The screw conveyor consists of screw blade, screw shaft, coupling, tubular trough, cover, inlet and outlet gates, bearings and drive mechanism.

A shaft with spiral screw revolves in the tubular trough. The screw shaft is supported by end and hanger bearings. The rotation of screw pushes the grain along the trough.

The screw blade or flight is a continuous one-piece helix, shaped from a flat strip of steel welded on to the shaft.

The screw shaft is usually a joint less tube with thick sides and a high tensile strength to reduce the weight.

Aim

To design shallow and deep bins

Theory

The structure behaves as a deep or shallow bin depending upon its relative dimensions such as depth and diameter or width. It is decided from the concept of the plane of rupture.

Plane of rupture: The plane of rupture is that surface down which a wedge of material bounded by one wall face, the free surface, and the plane of rupture would start sliding if bounding wall were to move.