Principles of Controlled Environment Flashcards
Green house environment is regulated by:
Light
Temperature
Relative humidity
Ventilation
Carbondioxide
Carbon dioxide
40% of dry matter of plant is composed of carbon.
During the day photosynthesis reduces CO2 level to 200 ppm from 345 ppm (0.03%).
Vantilation maintains ambiet CO2 level.
In winter ventilation maybe expensive as incoming air needs to be heated.
In such condition enrichment of CO2 in the greenhouse is followed.
Exact requirement of CO2 will vary based on other variables (light, temperature, nutrient level, cultivar, and degree of maturity).
Generally crops respond well to CO2 at 1000 to 1200 ppm.
Environmental control
Manual controlling-The temperature of the greenhouse is maintained manually.
At night the valves of heating pipe is manually regulated.
During the day, opening and closing of ventilators are regulated by hand.
To obtain desired temperature is difficult.
Controlled environment is based on the skill of the operator.
Thermostats-
The thermostat is an automatic device that sense the temperature and maintains the set temperature by activating or deactivating the equipment attached.
Use bimetallic stripe or thin metal tube filled with gas or liquid as sensors.
With change in temperature, volume of gas or liquid changes and the bimetallic stripe or metal tube moves which activates the mechanical switch.
These type of sensor is not highly accurate.
Active summer cooling system-
It is achieved by evaporative cooling process.
Basic principle used is that cooling takes place when the heat required for moisture evaporation is derived from the surrounding environment causing decrease in temperature.
Common active summer cooling system are:
Fan and pad cooling system-Along one wall of the green house pad is placed vertically on the wall
Pad is usually made of cross-fluted cellulose material
Exhaust fans are placed on the opposite wall
Warm outside air is drawn in through the pad
The supplied water in the pad, through the process of evaporation, absorbs heat from the air passing the pad as well as from the surrounding pad and frame causing cooling effect
It can lower temperature about 80% of the difference between the dry and wet bulb temperatures.
Complete evaporation of water droplets does not take place due to bigger water droplet.
Fog system
A high-pressure pumping apparatus generates fog containing water droplets with mean size of less than 10 microns using suitable nozzles.
These droplets are sufficiently small to stay suspended in air while they evaporate.
It can lower temperature about 100% of the difference between the dry and wet bulb temperatures.
Complete evaporation of the water droplets occurs due to its minute size.
It does not wet the plants thus reducing disease infestation.
Carbon dioxide enrichment methods
Green house ventilation
Microprocessors
Computerized control system
Heating system in controlled environment
Site selection, Heater, composting at one side of the greenhouse, bubble wraps, livestock, darker floor surface.
Jute bag, black stone wall and one side of the greenhouse, hot spring water in the green house and thermal mass, blower,
Black plastic at one side of the greenhouse, plastic poly tunnel inside the greenhouse,
Cover greenhouse full, mulching black, sunken greenhouse, LED lights, sunken bed, time of irrigation, hot air supply.
Carbon dioxide enrichment methods
In early 1960s, liquid CO2 was used where CO2 produced above the liquid was channeled to the green house.
Later generators were developed which were installed overhead in the greenhouse.
It is less expensive and produce CO2 in open-flame burners using kerosene, propane and natural gas. It also produces heat.
The light or time sensor is used to turn CO2 generator
on in the morning and off in the evening.
It is also turned off when ventilation is opened
Green house ventilation
Ventilation in the protected structure is essential for reducing temperature, replenishing CO2 and controlling relative humidity.
The ventilation system can either be:
Passive system (natural system)-
Usually practiced in tropics
With rise in temperature air gets heated and become lighter and rises up.
The warm air moves out and allows the cool air to flow in the green house.
Ventilations are located both on the roof and both side of the walls of the green house (10% of total area).
This system does not adequately cool the green house on hot days.
Thus, interior walls and floor were frequently injected with water on warm days.
Active system (forced ventilation)-
Mechanical devices such as fans are used to expel the air .
It will provide uniform cooling
This includes summer fan and pad cooling system and fog cooling system.
Microprocessors
It’s a simple computer dedicated for controlling greenhouse environment.
It can operate and control various devices (maximum 20).
They can receive signals of several types such as temperature, light intensity, rain and wind speed.
Example: a microprocessors can operate ventilators based on information from sensor for the wind direction and speed.
Computers
Computer system can provide fully integrated control of temperature, humidity, irrigation, fertilization, CO2, light and shade.
Precise control can save 15-50% energy, water, chemical and pesticide.
Computer systems receive signals from all sensors, evaluate conditions and send appropriate commands every minute to each equipment.
It also collects and record data, produce graphs of past and current environmental conditions.
Proper software programme which use environmental parameters as input from different sensors, can effectively coordinate all the equipment overlap.
However, success of production system depends on the grower’s knowledge of the system and crop management.
