Design of Environmental Control System for Closed Layer House

0 Introduction

The laying hen house is a fully enclosed system in structure. The internal environment of the hen house is restricted and affected by the design structure, forming a so-called "chicken house microclimate" that is different from the external environment, mainly including indoor temperature, humidity, light, carbon dioxide, ammonia and hydrogen sulfide and other factors [1-4]. The fully enclosed structure of the chicken house determines the material and energy exchange between the chicken house and the outside world, which in turn causes changes in the microclimate environment of the chicken house. This change will affect the growth of laying hens and their egg production rate to a certain extent [5-6]. Therefore, the main function of the chicken house environment monitoring system designed in this paper is to realize the intelligent monitoring and control of environmental factors such as temperature, humidity, light intensity and concentration of harmful gases (carbon dioxide, ammonia and hydrogen sulfide) in the chicken house.

1 System Construction

This monitoring system uses the host computer to periodically send monitoring commands to each monitoring point, and receive data sent by each monitoring point, process, display and save the collected data, and send execution instructions to the unit that specifically controls the wet curtain fan (including spray), thereby realizing the control of the actuator, as shown in Figure 1.

1.1 Host Computer

The host computer of this design is a PC. The main functions of the host computer are: first, to send data acquisition commands to the lower computer through RS-485 serial communication, and to receive data collected by the sensor transmitted by the lower computer; second, to set the address substation number, time, alarm upper and lower thresholds and control parameters of the lower computer on the host computer interface; third, to display and save the collected data in the database, and to issue the instructions required by the actuator; fourth, to view the historical data, and to display, analyze and print the historical curves.

1.2 Intelligent Monitoring Points

The four intelligent monitoring points and one control point, namely the lower computer, use the ARM series model LPC2132 microcontroller of PHILIPS Company as the microcontroller, and use 8-way switch output and environmental factor data input. Among them, the environmental factor data includes 6 quantities such as temperature, humidity, light intensity, carbon dioxide, ammonia and hydrogen sulfide. The principle block diagram of the intelligent monitoring point is shown in Figure 2.

The temperature and humidity control of chicken houses is an important research object of this topic. The temperature and humidity of chicken houses have the following characteristics: nonlinearity, uneven distribution, time-varying, control delay, multivariable coupling, etc. At the same time, the action of the actuator (such as the wet curtain fan) does not only affect a certain factor, such as the concentration of harmful gases (carbon dioxide, ammonia and hydrogen sulfide). Therefore, it is difficult to achieve precise control, which requires coordination and cooperation in many aspects of the system. Therefore, a full closed-loop control strategy is adopted for the system, that is, when the indoor temperature and humidity rise, the sensor transmits the sampled value to the control unit, and the control unit compares it with the user set value. When the absolute value of the deviation is greater than the offset value set by the user, it issues a command to make the actuator act. The control process is shown in Figure 3. This closed-loop control is also applicable to the regulation of environmental factors such as light intensity and the concentration of harmful gases (carbon dioxide, ammonia and hydrogen sulfide).

The main functions of the intelligent monitoring point are as follows: First, the collected data can be displayed on the monitor; second, data such as temperature, humidity, light intensity, carbon dioxide, ammonia and hydrogen sulfide can be collected through different types of sensors, and environmental factors such as temperature, humidity, light intensity, carbon dioxide, ammonia and hydrogen sulfide can be controlled, among which temperature and humidity can be controlled by fuzzy control algorithm first; third, parameters can be set through the keyboard, such as sound and light alarm, and can receive commands from the host computer to achieve parameter setting and output control; fourth, commands sent by the host computer can be received through the serial communication interface, and the collected data and control information can be transmitted to the host computer to achieve communication with the host computer; fifth, real-time clock control can provide system data collection time display and store data by time; sixth, manual/automatic control mode can be switched by keystroke; seventh, it can switch to the regulation of one or several monitoring quantities in real time.

2 System hardware selection and typical circuit design

According to the environmental characteristics of the closed laying hen house, sensors with different measurement functions should have long-term stability, enable the system to truly respond quickly, and regulate the environment efficiently. The data collection range should meet the environmental factor requirements of laying hen activities. For this reason, when designing the system hardware, digital temperature sensor DS18B20, polymer capacitive humidity sensor HS1101 of HU-MIREL, and light intensity digital conversion chip TSL2561 launched by TAGS of the United States were selected.

The monitoring sensors for harmful gas concentrations are: CO2 concentration sensor uses TGS4160 produced by FIGARO of the United States, NH3 sensor model MIC-NH3 intelligent sensor, and hydrogen sulfide sensor model (H2S sensor) M-100.

2.1 Design of temperature measurement circuit

DS18B20 has two power supply modes: parasitic power supply and separate power supply. In order to ensure the accuracy of the measurement results, this project adopts separate power supply. Figure 4 is a temperature measurement circuit for laying hens. The single bus P0.15 is connected to the MCU LPC2132 pin PO.15/EINT2, and its pull-up resistor is 4.7k ohms. When the bus is idle, its working state is high level. [page]

2.2 Design of humidity measurement circuit

The humidity sensor HS1101 of the laying hen house is connected to the pin P0.17 of the single-chip microcomputer LPC2132 as a variable capacitor. The reason why the control voltage end uses the resistor R1=909kΩ instead of the 0.1μF capacitor is to introduce a temperature coefficient to match the temperature coefficient of the humidity sensor HS1101. R3=1kΩ is a short-circuit protection resistor. In order to make the duty cycle as close to 50% as possible, R4 should be selected to be much smaller than R2, but the output frequency of the circuit should be around 6660Hz. Here, R4=49.4kΩ and R2=576kΩ are selected, as shown in Figure 5.

2.3 Design of light intensity measurement circuit

The light intensity sensor TSL2561 in the laying hen house is accessed through the I2C bus protocol. The microcontroller LPC2132 has an I2C bus controller inside. The clock line and data line of the bus are directly connected to the SCL and SDA of the I2C bus of TSL2561, respectively, and the INT pin is connected to the external interrupt pin EINT3 of the microcontroller LPC2132. The light intensity measurement circuit is shown in Figure 6.

2.4 Design of CO2 measurement circuit

In order to keep the CO2 sensor in the laying hen house at the most sensitive temperature, it is generally necessary to provide a heating voltage to the heater for heating. However, the change of the heating voltage will directly affect the stability of the sensor. Therefore, the heating voltage must be stable and its range should be within (5.0±0.2)VDC. Here, pin 1 is connected to a 5.0V voltage. CO: measurement circuit, as shown in Figure 7. The output voltage of the TGS4160 CO2 sensor is (0-3.0)V, so a 3.3V reference voltage can be used and it can be directly connected to the A/D conversion pin P0.27 of the single-chip microcomputer LPC2132.

3 Software Design of the Environmental Monitoring System for Layer Houses

3.1 Main Program Design of Temperature and Humidity Measurement and Control in Typical Chicken Houses

When the temperature in the layer house is ≥ target temperature + temperature offset (temperature setting upper limit), the wet curtain flip window is started. When the wet curtain flip window is opened to the end, the end limit switch of the flip window motor is closed. After the closing signal is transmitted back to the controller, the controller cancels the "wet curtain flip window open" signal and drives the fan and wet curtain to run at the same time. When the temperature in the chicken house is ≤ target temperature + temperature offset (temperature setting lower limit), the fan and wet curtain are turned off to enter the system timing. When the timing time is up, the control process ends once. The program control process is shown in Figure 8.

When the humidity in the laying hen house is ≤ target humidity + humidity bias (lower limit of humidity setting), the spray device is started to spray clean water, so that the humidity of the chicken house can be restored; when the humidity of the chicken house is ≥ target humidity + humidity bias (upper limit of humidity setting), the spray device is turned off and the system timing is entered. When the timing time is up, the humidity control process in the chicken house ends. [page]

3.2 Design of the temperature acquisition program of the laying hen house

The chicken house temperature control system uses the programmable digital DS18B20 temperature sensor produced by DALLAS Company of the United States. It directly outputs digital signals and does not require signal amplification. It adopts a single bus structure and does not require other external components. The single-line communication function of DS18B20 is completed in time-sharing and follows a strict concept of time. The microcontroller LPC2132 must strictly follow the protocol for its various operations, otherwise the temperature data cannot be read. The flow chart of the temperature acquisition program of the laying hen house is shown in Figure 9.

4 Experimental design of the environmental control system for laying hens

The environmental control system for laying hens was tested for temperature and humidity measurement and control. The test time was from July 29 to August 2, 2008, and the test site was Beixin Town, Qidong City, Jiangsu Province. In order to compare the measurement accuracy of temperature and humidity, dry-bulb thermometers were arranged in different parts of the chicken house space. Four sections at 9, 37, 79, and 107 m from the door were selected for the test. The temperature distribution state in the height direction was analyzed, as shown in Figure 10. From the height direction, the temperature difference in the height direction between the front and rear ends of the chicken cage is not large. This is because the two ends of the chicken cage are closer to the air inlet and the exhaust port, respectively, and are greatly affected by the leakage hot air and the hot air leaving the house. The cage frame in the middle part is less affected by the leakage hot air and the hot air leaving the house, and the overall temperature increases from the bottom of the cage to the top of the cage. This is related to the factors such as the low density of hot air and the relatively high distribution position. Compared with laying hen houses without environmental control systems, laying hens in houses with environmental control systems have an egg production rate 15.3% higher. This shows that the designed closed environmental monitoring and control system for laying hen houses has extremely important promotion significance in the poultry farming industry.

Figure 10 Temperature distribution in the vertical direction of the house in summer

5 Conclusion

The closed laying hen house environment system is based on field control. In the next step of research, the Internet access function of the PC will be used to connect to the Internet, and the field collected data will be sent to the database server of the monitoring and early warning control center in real time to realize remote monitoring and control of the chicken house environment.