GREENHOUSES/ POLYHOUSES AND ITS IMPORTANCE

The Greenhouses/polyhouses are constructed with the help of ultraviolet plastic sheets, so that they may last for more than 5 years. The structure is covered with 1501 m thick plastic sheet. The structure is prepared with the bamboos or iron pipes. Iron pipe structure is costly but more durable than bamboo.

Generally the length of the polyhouse is 25-30 feet and width 4-5 feet. The direction of polyhouse is always East to West, so that the maximum sunshine is available. The house should not be constructed in shade. The size of polyhouse may differ depending on the necessity. The polyhouses are kept cold or hot depending upon the season.

Use of Greenhouses:

From the point of view of earning more profit only such off-season crops should be grown, which are being sold at higher prices in the market. Big hotels in cities are mostly in the need of off-season vegetables and so is the case with some prosperous people in big cities. In such areas and also in the hill and remote regions where fresh vegetables are required regularly for meeting out the requirements of security forces, the construction of polyhouses is more lucrative and is a must.

The crops grown under the polyhouse are safe from unfavourable environment and hailstorm, heavy rains or scorching sunshine, etc. Crops of the polyhouse can be saved from birds and other wild animals. The humidity of polyhouse is not adversely affected by evaporation resulting in less requirement of water. In limited area of polyhouse, insects and pests control is also easy and less expensive.

By adopting the modern technology of polyhouse, the difference in the demand and supply of off-season vegetables and fruits etc. can be minimised. This facilitates in maintaining the quality of the product also.

Greenhouse can be used for:

·        Producing half hardy perennials or bedding annually grown from seed both during sowing and pricking out.

·        Protect tender plants and bulbs during the winter months.

·        Grow hobby plants such as chrysanthemums, fuschia's or exotic orchids.

·        Cultivate indoor pot plants.

·        Cultivate alpine species.

·        Use it for commercial purposes.

Components of Green House

1. Natural Roof and side wall ventilation system.
2. UV stabilized covering materials of Polyethylene / Polycarbonate / Acrylic.
3. Cellulose Cooling Pad and Exhaust Fan System.
4. Heating system in cold climate.
5. CO2 Generator.
6. Shading / Thermal Net
7. Trellising system for vegetable
8. Trestles system for flowers.
9. Green House G.I. structure.
10. Covering material-UV stabilized Polyethylene / Polycarbonate / Acrylic.
11. Root Ventilation & Side wall roll up curtains.
12. Cooling pad and Fan System.
13. Shading / Thermal net Manually / motorized.
14. Micro Irrigation System.
15. Fertigation System
16. Misting System.
17. Heating System.
18. CO2 Generator.
19. Control System - Manual / Semi Automatic / Automatic. Fully Computerized / Weather Station.
20. Planting material, soil media.

Fully Computerized Control System

Most of the time, the owners prefer Mutually Controlled System or Semi Automatic Controlled System for green house, because of low investment. But in such type of Control Systems it requires a lot of attention and care. Also it is very difficult and cumbersome to maintain uniform environment inside the Green House. Ultimately this affects crop production, non uniform growth and low quality of the crop.

Computerized Control System is the solution to come over this problem and to maximize returns. Computer provides a faster and precise operation in the Green House. Also it stores, displays and prints the Green House information as needed. Computer can do the following operations as per the pre-scheduled programme:

1.      Starting and closing of Micro Irrigation System.

2.      Application of Liquid Fertilizer or Water Soluble Fertilizer (N:P:K) and other Nutrients to the plant.

3.      Operation of Misting System as required.

4.      Opening and closing of ventilators and side wall roll up curtains as needed.

5.      Operation of shading net / Thermal screen.

6.      Operation of cooling pad and fan.

7.      Operation of heating system.

8.      Operation of CO2 Generator, Climate Control, Temperature, Humidity, Heat Radiation, Control of EC, PH, PPM level in irrigation water etc. as required to the plant.

benefits of instrumentation in green house

1. Optimised Humidity control

2. Irrigation and water saving

3. Nutrients supply

4. Quality

5. Energy conservation

6. Development of a modern Management and control package.

1. Optimised Humidity control

 

Figure 1: Schematic of the tomato plant growth where 5, 6 and 7 refer to truss number

In commercial greenhouses the relative humidity is constantly varying and the aim of humidity control is to avoid environments which would lead to a reduction in yield and/or quality.  A humidity event, when leaf transpiration rate is low resulting in symptoms of calcium deficiency occurring, influences the growth of leaves associated with several trusses (Hamer and Belay, 1997). An event on one day can result in the reduction of yield and quality of fruit harvested over about a four to five week period (Figure 1). A modification of the environment at one time of the year does not result in a return until later in the season. Crop values change throughout a season with the lowest values when supplies are at a peak, general in mid-season. The techniques for control must be cost-effective so that the benefits of a control strategy in terms of yield and quality are in excess of the costs of carrying out the dehumidification.

As there is a well-known need for humidity control at the lower end of the water-uptake range, a dynamic crop growth model (Hamer, 1997)was developed from measurements taken during the course of the Macqu project. Simulations using a model which predicted conditions inside the greenhouse enabled the cost benefit of de-humidification to be evaluated. A combination of ventilation and heating proved to be the only economically viable means of dehumidification in which the ventilation rates were constrained by restricting the angle of opening of the ventilators.

It was concluded that both visual and internal quality parameters can be modified through environmental manipulations. The techniques that have been developed , in course of Macqu project, can be implemented in a management system that reacts to on-line observations.

    

2. Irrigation and water saving

Protected crops have a high water requirement. Irrigation control is important to ensure that the plants needs can be met without overwatering. Overwatering has the potential to cause environmental damage particularly if the excess irrigation water containing fertilisers enters the ground water system.

The control of the water supply can be used as a management tools to control crop growth and to improve the quality of produce. A minor water requirement of the crop is for plant growth which is typically less than 4%. However, over short periods when transpiration rates are low the proportion of water used for storage compared to transpiration can be high.

To define an effective control strategy it is necessary to predict how the uptake of water by the plant depends on the climatic conditions, this can be achieved using a model. (Hamer, P.J.C., 1997). To ensure that the crop receives adequate irrigation throughout a season under all the environmental conditions experienced, the model must be robust, which implies simplicity, and that any input values needed by the model must be easily and reliably measurable. An irrigation model for greenhouse tomatoes (Hamer, 1997) was developed and validated, in course of Macqu project.

3. Nutrients supply

·      Feedfack control of the water and nutrient supply

Keeping the rate of water and nutrient drainage constant in a direct feedback control system, thus ensuring the compensation of both water and nutrient uptake by the plants, was shown, during Macqu project, to be viable in closed growing systems with a drain flow sensor and also in open growing systems when using a starting gully and drain flow sensor.  A tipping-bucket sensor was used to monitor the output of the controlled system and provide the feedback signal to the controller (Th. H. Gieling, A.J.W. van Antwerpen, J. Bontsema, M.HM.H Bastings, 1996).  The results showed very close control of the drainage flow, keeping it constant for long periods of time.

The value of the drain water flow can be chosen freely. It can be lowered in such a way, that only a minimal amount is supplied, but still all the plants in the greenhouse are receiving water. In this way, the amount of return water is minimized, giving rise to a reduction in the amount of water that has to be cleaned before being re-used, hence to a cost reduction. A constant drain return will also allow for an optimal usage of  connected equipment, which close the loop, like: drain  water cleaning and re-fertilizer equipment. No harm to the plants is risked, since the controlled supply system will act almost instantaneously and will immediately compensate any change in drain water return.

By closely matching the supply of irrigation water to the crop requirements, the discharge of fertilisers into the soil environment and the consumption of water can be reduced substantially. Model based control and constant drain return feedback control proved to be a reliable approach. It has been proved that improvements to growing system can reduce leaching of irrigation water.

·      “Tichelmann” lay-out

An irrigation review was undertaken, during Macqu project, which included methods for nutrient transport to the roots and the uptake of nutrients by the roots (Gieling, Th. H, J. Bontsema, A.W.J. van Antwerpen & L.J.S. Lukasse, 1995).  In order to improve the dynamic properties (dead time and delay times) of water supply systems, the so-called "Tichelmann" lay-out was proposed.  The properties of this lay-out have been described in a model based on "First Principles". It was tested by simulation and installed in a greenhouse growing system.  The results have been disseminated at two Horticultural Engineering Shows (NTV 1995 and 1996, The Netherlands) and  subsequently the system has been widely accepted by industry.

It was shown that improvements to the water supply lay-out considerably reduced the time delays and dead times in the supply system.

Tichelmann lay-out description (figure 2): The outlet of the system situates on the opposite side of the inlet . Thus, the route of the water through the system is equal for all supply lines and the length of the routes in the system is equal for all supply lines, the distribution of the water is nearly uniform.

 

·      Hydroponic system

During Macqu an innovative dosing device for hydroponic systems has been designed and tested. The device was filed with Greek Industrial Intellectual Property Rights for a patent. It provides a cost effective, reliable and of high accuracy method for mixing corrosive chemicals. The overall system combined with a feedback loop in Macqu software accurately controls nutrients concentrations (EC) and pH. Its main innovative feature is that it can accept as many solution tanks as desired with very limited additional hardware. Proportions of the different tanks are set in a simple dialog with Macqu while total concentration (EC) and pH is control by feedback to high accuracy. The control loop was tuned to quickly respond to system disturbances and can maintain high accuracy in both “mixing tank systems” and “on line mixing systems”.

 

4. Quality

 Given sufficient knowledge about crop response, a management system could make an appropriate use of available tools for manipulating indoor climate and nutrition, in order to maximize yield value. In particular, one could choose to accept a decrease in yield, if there was a sufficient increment in quality of the product (C. Stanghellini, W. van Meurs, F. Corver E. van Dullemen and L. Simonse, 1997). Such a cost-benefit weighting obviously requires some knowledge about the crop response to both nutrition and selected factors of the climate within the house.

Research in course of Macqu project showed that:

·      Quality vs nutrition

High salinity reduces yield by reducing the influx of water to fruit. The observed reduction in fruit weight was 2.7 % for each dS m-1 by which the salinity (EC) in the root environment exceeded 2 dS m-1. High salinity is associated (in conditions of large water uptake) with blossom-end rot (BER), which reduces the number of marketable fruits by 3.2% for each dS m-1 that the EC exceeds 2 ds m-1.

·      Quality vs climate

Depressing water uptake by imposing a high greenhouse humidity significantly reduces the incidence of BER (C. Stanghellini, W. T.M. van Meurs, F.G.M. Corver, E. van Dullemen and L.Simonse, 1996).  However, high humidity reduces transpiration which can produce calcium deficiency symptoms on leaves, and this can lead to yield and quality losses in tomato fruit. Water uptake can be increased by reducing the greenhouse humidity.

5. Energy conservation

The use of alternative energy sources and energy saving methods can reduce the emissions of contaminants into the environment and also increase energy efficiency thus improving the competitiveness of greenhouse production.

A number of techniques have been tested to investigate energy use and cost saving methods and useful tools have been developed under the MACQU project.

·      Energy saving

Greenhouse energy use models are practical ways to predict the behaviour of the greenhouse and to improve energy management, and three such models were developed in this project.

A dynamic greenhouse model was developed and validated to predict the response of the greenhouse environment to the external weather, the internal environment conditioning devices and the control actions (Navas L.M., De la Plaza S., Garcia J.L., Luna L. and Benavente R.M., 1996).

A second model, of the step-wise steady state type, was developed to estimate greenhouse energy needs with different energy saving measures and to calculate the energy needs covered by conventional or alternative energy sources (Garcia J.L., De la Plaza S., Navas L.M., Benavente R.M. and Luna L., 1996). This model has been included in a computer program and the logic code produced was integrated in the MACQU program.

Other models were developed for energy and investment cost analysis with different energy sources (heat pump, solar energy and cogeneration) and to check the experimental results, this showed that heat pumps could be feasible under certain conditions.

·      Energy management

An approach to solving the problem of remotely operating a complex greenhouse, designed for best use of equipment and resources, involves the design of an end-to-end system that includes the human operator as a critical component.

Therefore the growers' intuition and experience is allowed to intervene at different stages, and user goals can be expressed at different levels of management, from rules about quality and yield, down to set-point manipulation (figure 3). The remote controller unit (RCU) handles all of the closed loop controls for the greenhouse operation, such as heating or ventilator degree setting, mist operation, valve setting for irrigation and nutrient supply, etc. All RCU functions are parametric and can autonomously do scheduling of operations, take energy saving measures etc, in the framework of short to medium term planning. Higher level decisions, made at the central station, are concerned with long and medium term strategies and operator's goals, and are passed down to the RCU as parameters of reference generating functions for real time set-point derivation.

                      

                      Figure 3: Different levels of operators input and rules manipulating adaptive set-point derivation.

 An energy management rule-base is being prepared which will do off-line energy utilization planning regarding energy availability, cost and projected energy needs, as well as on-line energy saving, based on a diurnal reference trajectory adjustment (figure 3).

·      Heating technologies

Experiments were conducted with alternative energy sources and localised heating as an energy saving method (De la Plaza S., Garcia, J.L., Navas, L.M., Benavente R.M. and Luna L., 1996). The results showed that localised substrate heating could be economically feasible in ornamentals crops (geranium, gerbera) when supplied with hot water from an oil or gas fuelled boiler; but the feasibility of electricity was strongly dependent on the price of the product; it was not feasible for tomato production.  A heated concrete floor, another localised heating method, showed an energy saving up to 20%.  The feasibility of this system was proved with crops having low canopies and a high temperature requirement.

Energy use analyses were carried out for seven European locations to determine the economical applicability of the systems related to investment costs, and fuel and electricity prices.  The use of localised heating, industrial thermal effluents and co-generation were the best techniques to obtain a higher energy efficiency and a reduction of environmental pollution.

6. Development of a modern Management and control package.

 

A system was designed, to be  “OPEN” and with the innovative features of Virtual Variables and MACQU-native KBS, it is possible to incorporate any new functionality without programming. The system was successfully installed at the evaluation site (MAICH) and tested for the period of March through June 97.

The development of a modern Control and Management system for greenhouses (N. Sigrimis, A. Anastasiou, V.Vogli, 1997)  used recent advances in software design and development tools to provide a “no programming needed OPEN system”. The system provides a vehicle through which all research achievements can be immediately implemented in the field. The main innovative features implemented to provide such a flexible system are:

1.      Functional objects: Object oriented design not only on the programming style but also on the “user_functionality”. A complete set of “prime functions”, needed at the different signal processing stages (input-processing-output), were identified and designed as independent objects. These objects can be specified and chained to provide a “custom” higher level function, i.e. management of supplementary lights.

2.      Virtual variables (VV): The system starts with no variables, other than hardware related, defined. At any time the “user” can institute, in the field, new variables as functions of other variables. Such a nesting has no limit (except physical memory). A rich set of function templates (library) has been designed-in, from which the user can select his signal processing building blocks. Polynomials, adjustable Time-Integrated-Variables, multi-in-one-out, thresholds-decisions, timers and multi-point day_clocks, , hard and soft events, are some of such VVs which can be defined and used as input to other functions.

3.      Virtual control loops: Almost any control philosophy can be implemented using a well defined chain of building blocks and smart virtual variables. Non-linear PIDs, configurable output functions and functional enable/disable switches are the tools to build control loops, which may also be nested or cascaded. Virtual variables can implement models used for adaptive set-point control (optimize greenhouse performance) or for a feed-forward action (optimize loop performance).

4.      KBS-Tasks/subtasks: Higher level management can be implemented using a Fuzzy Logic, rule based, expert system, native of Macqu. This system provides input, output and rule editor on line. The outputs can directly affect the greenhouse equipment or may influence control loops, previously defined in the greenhouse computer. The rules may refer to (consequent) tasks which are open objects including one or more subtasks. Subtasks are the “modes” of operation of equipment drivers, programmed in the greenhouse computer. In this way a Fuzzy Logic Controller, native of Macqu, can interact with or overtake the control functions of the greenhouse computer. Such a high degree of functionality needs “careful set-up” /the present status/, or a well designed “supervisor”/macqu evolution/.

  

THE  EXPECTED  BENEFITS  ARE:

  Technical:

The determination of the most cost effective method for limiting greenhouse humidity. The development of a new and effective way of controlling plant irrigation, which could have application on open field cultivation as well. Tuning heating system efficiency with the phase of the protected crop. Standardisation of conventional sensors and development of new sensing techniques to enable "quality control" in prime production. Advanced concepts of Information technologies to provide a vehicle for speeding up the transfer of research results to practice.

Scientific:

The development of a method of predicting plant water and nutrient requirement based on easily measured weather variables. A significant advance in the simulation techniques used to predict the environment in cropped enclosures. Innovative sensing of plant physiological responses, including early nonvisible symptoms of disease onset. The development of on-line techniques for the real time optimisation, cost vs quality-grade, of controlled conditions.

Economic:

Reduction of precious water and nutrient chemicals consumption, by an amount of up to 40% in greenhouse production and ensure quality by water availability and balanced nutrient supply. This will be of particular importance in regions of scarce water. Reduction of labour cost and pesticides with the "soilless closed irrigation" systems. Optimal control of greenhouse humidity and of energy utilisation will enable grower income be maximised. An integrated product will satisfy constraints for both; the private competitiveness and the public benefit.

Environment:

A reduction in pollution caused by the fertilisers contained in excess irrigation water drained to the soil. Reduction of crop protection chemicals (reaching the consumer directly through the product and indirectly through the environment) by: controlling humidity, early detection of diseases, and finely controlled closed irrigation systems.