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.
- Natural Roof and side wall ventilation system.
- UV stabilized covering materials of Polyethylene /
Polycarbonate / Acrylic.
- Cellulose Cooling Pad and Exhaust Fan System.
- Heating system in cold climate.
- CO2 Generator.
- Shading / Thermal Net
- Trellising system for vegetable
- Trestles system for flowers.
- Green House G.I. structure.
- Covering material-UV stabilized Polyethylene /
Polycarbonate / Acrylic.
- Root Ventilation & Side wall roll up curtains.
- Cooling pad and Fan System.
- Shading / Thermal net Manually / motorized.
- Micro Irrigation System.
- Fertigation System
- Misting System.
- Heating System.
- CO2 Generator.
- Control System - Manual / Semi Automatic / Automatic.
Fully Computerized / Weather Station.
- Planting material, soil media.
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.
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.
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.
· 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”.
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.
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.
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.
