greenhouse climate control system

Installing various environmental control equipment inside the greenhouse and using an automatic control system to adjust the internal microclimate has become the basic consensus among those engaged in greenhouse cultivation. The advancement of technology is endless. The innovation and improvement of environmental control technology is closely related to the update and progress of other technologies.

1. Sensing system

(1) Sensors Sensing systems used in greenhouse cultivation include:

A. Gas environment: temperature, relative humidity, sunlight, wind speed, wind pressure, carbon dioxide concentration, etc.

B. Root environment: substrate temperature, pH value, EC value, each single ion concentration, substrate moisture content, etc.

C. Physiological state of crops: leaf temperature, leaf area, leaf angle, chlorophyll content, sugar content, N concentration, stomatal opening, pathogen density, etc.

(2) Performance requirements of sensors The special performance requirements of the sensors used in the greenhouse environment control system:

A. The accuracy range is 25% of the control requirement range

B. Can resist high temperature, high humidity and dusty environment.

C. The sensing operation of the sensor does not hinder the growth of crops. For example, the measurement of leaf temperature should be performed by near-infrared non-contact technology, and contact wires cannot be inserted into the leaf body.

(3) The location of the sensor

Sensor placement is extremely important. It must be representative and represent the real environment of the crops inside the greenhouse. For example, if the substrate moisture meter is placed in a plant container or a plant growth bed close to the aisle, its moisture measurement value will be low. On the other hand, the placement of the sensor should not affect the measurement accuracy due to other objects. For example, if the sunshine meter is affected by the shadow of the beam, the measured value will be low. The thermometer is fixed on the beam and column, and the measured temperature value is easily affected by the heat absorption and heat dissipation of the metal material.

(4) Maintenance of sensors

The temperature and humidity sensor should avoid direct sunlight. There must be a dust-proof device above the sunshine meter so as not to affect the wavelength of sunlight and the angle of sunlight deviation. The pH, moisture and other measuring electrodes inside the medium must be resistant to acid and alkali. The overall system needs to have an electric shock protection device, which can withstand sudden voltage changes and external static electricity.

(5) Calibration of the sensor

Various sensors for greenhouse environment control output current or voltage signals for easy connection with industrial control systems. However, the measurement performance of sensors developed on the basis of electrical principles is affected by nonlinearity, hysteresis effects, aging phenomena, etc., and their accuracy and reproducibility change with the environment and time of use. Therefore, regular calibration is required to ensure the accuracy of the sensor. The measured performance is correctly available. On the other hand, it is necessary to consider whether the built-in formula of the sensor is applicable.

The accuracy of the sensor directly affects the success or failure of the control operation, but the calibration operation of the sensor determines its measurement performance. Calibration operations require the use of standard substances or the establishment of a standard environment. This calibration standard establishment work has established a system in the measurement industry, which can be introduced for performance calibration of environmental control sensors.

2. Control operating system

The control system is composed of three elements: environmental control equipment, sensing system and control strategy. Environmental control equipment such as negative pressure fans, internal circulation fans, water walls, heating machines, fogging tools, etc. If the performance of mechanical equipment is poor or fails, the function of environmental regulation will not be able to play. Therefore, the basic work of controlling the greenhouse environment is the regular maintenance of the equipment. The work that needs to be carried out includes checking the blocking degree of the mist nozzle, checking the tightness of the fan belt, and maintaining various sensors.
2. Control operating system

The control system is composed of three elements: environmental control equipment, sensing system and control strategy. Environmental control equipment such as negative pressure fans, internal circulation fans, water walls, heating machines, fogging tools, etc. If the performance of mechanical equipment is poor or fails, the function of environmental regulation will not be able to play. Therefore, the basic work of controlling the greenhouse environment is the regular maintenance of the equipment. The work that needs to be carried out includes checking the blocking degree of the mist nozzle, checking the tightness of the fan belt, and maintaining various sensors.

(2) Process control

The feature of this control strategy is to compare one sensing signal with multiple setting values, and then control different devices separately. For example, the temperature inside the greenhouse is compared with the set temperature of the array to control the heating machine, internal circulation fan, external air negative pressure fan, water wall and mist in sequence.

The error range of the control is related to the controller performance.

(3) Microcomputer control

Using the computing power of the microcomputer, the microclimate of multiple sections or multiple greenhouses can be controlled simultaneously. Another feature of using a microcomputer is that it can record and store the sensing value of the microclimate inside and outside the greenhouse and the action time of various environmental control equipment, so managers can track the past cultivation process. Since this type of equipment is standardized, data transmission can be easily performed.

(4) Integrated control

This kind of control technology uses the computing power, data and data storage capacity of the microcomputer, and cooperates with the establishment of the crop marketing database to establish a computing system inside the control system. Based on this system, the data is analyzed, and the judgment and synthesis are made based on the previous cultivation data, which becomes the optimal control strategy. Using this strategy, the control parameters of the microclimate in the greenhouse are not set as fixed values, but variable values. The mode of action of such control systems has different levels:
A. Aim for the best environment for crop growth: to make crops grow faster and with the best quality.

B. Target crop growth costs: For example, raising the temperature can make crops grow faster and be sold earlier. However, more energy costs are added, so the use of integrated mode control can evaluate the most appropriate environmental control parameters based on cost conditions and market product prices, focusing on the best profit.

(5) Control of knowledge system

This control system contains a knowledge system for "intelligence" judgment, and the result of this intellectual judgment is used as a control decision to formulate control parameters (such as temperature, humidity, sunlight, substrate moisture, etc.), and then command the environmental control equipment . Since the knowledge system can cover the data of the management operation, it can also be used to command and manage the equipment. Therefore, the control system can be used both for greenhouse environment control and production management operation control.

The knowledge system includes physiological models expressed by mathematical formulas and professional data processed by logic programs. The knowledge system consists of a series of databases and mathematical models. Examples of its application are as follows:
1. Greenhouse environmental control

The user inputs the name of the crop and variety planted in the greenhouse, and the cultivation conditions of this variety (day and night temperature, relative humidity, light quantity, photoperiod, medium moisture, electrical conductivity, etc.) have been pre-stored in the cultivation database of the knowledge system. This is the environment Controls the default value of the system. If the default value differs from the microclimate measurement value inside the greenhouse, and the difference value is higher than the control tolerance deviation value, the knowledge system uses the greenhouse microclimate model calculation to control the adjustment amount and adjustment sequence of the environmental control equipment. On the other hand, if the internal environmental conditions are close to the default value, but the measured value of the atmospheric environment and the calculation of the microclimate model show that the external environment will soon affect the internal microclimate, the knowledge system can activate the environmental control equipment in advance to respond in advance, and carry out such a preliminary Taught environmental control operations.
Sensing data from the media environment or crop pest monitoring can determine whether crops need to be irrigated, fertilized, and pesticides applied. While performing these management operations, the environmental control system can also make corresponding adjustments, such as maintaining ventilation and Accelerates the evaporation of water above the leaves.

The knowledge system can be used to recalculate the cost of operations in the case of changing operating cost conditions in the greenhouse (for example, changes in energy costs). Under the condition of not affecting the market supply schedule, the setting parameters of the greenhouse environment control can be further adjusted.
Due to changes in market information, such as the advance or delay of delivery time requirements, the knowledge system can be calculated using physiological models to determine the conditions for controlling the greenhouse environment or fertilization and water supply operations under the requirements of adjusting the production schedule. changes, which are then used to reassess production costs.

The crop production status fails to reach the production quality management point or symptoms appear. The knowledge system can use the past microclimate data of the greenhouse and the current physiological state of the crop to identify the cause and deal with it. For example, causes of poor crop growth can be categorized separately into

1. The growth environment (air or underground) is not suitable for this variety,

2. The management method is not suitable (too much or too little water and fertilizer),

3. Invasion of diseases and insect pests or virus impact.
3. Relay station

In the above control operations, the greenhouse internal sensing system, knowledge system, and controller together form a relay station for greenhouse environment control operations. The data received by this relay station includes the atmospheric environment data transmitted by the central management system, the microclimate adjustment setting value of the greenhouse, and the parameters input by the controller. These external data are compared with greenhouse microclimate data and crop physiological condition sensing data, and then evaluated and compared by the knowledge system in the controller to control the environment control equipment.
The characteristic of this type of relay station is that one relay station controls one or several greenhouse units. The relay station can receive the data from the central management system, and also transmit the sensing data and the control actions of each device to the central management system, but it does not accept the command signal from the central management system. This kind of control function lies in that only on-site operators can input commands, and remote personnel cannot directly engage in remote operations.

The abnormal signal warning system can be used in conjunction with this relay station system. And the responsible personnel can be notified by wired or wireless communication

4. Signal and data transmission

The data transmission from the relay station to the central management system can be transmitted by wired or wireless means. Since the transmission of data and data is a standardized operation in the industry, it can be directly used in the greenhouse environment control system.
5. Central management system

This central management system has the following functions:

1. Collect the measured data of the atmospheric environment, record it and send it to each relay station.

2. Accept the microclimate data and equipment action information of each greenhouse transmitted by each relay station.

3. Based on changes in operating cost conditions or operating schedules, the built-in knowledge system is used for calculation and evaluation, and the internal microclimate parameters and management operating conditions of the greenhouse are re-determined, and then sent to the relay station, and then handed over to the management personnel to input and control according to the local conditions system.

4. Compare the crop growth information collected every fixed time, and use quality control technology to evaluate whether it meets the predetermined growth progress. If there are differences in growth traits and quality (such as nitrogen fertilizer content, stem length, etc.), judge based on the existing production process information and crop physiological data, as a reference for the adjustment and management of environmental control parameters.

5. The built-in website of the management system can provide the company's administrative units to use the network to obtain relevant production information in different regions. The growth status of crops can be provided to downstream customers for online viewing through the network.