Design of solar semiconductor refrigeration and air conditioning control device

O Introduction

Solar semiconductor refrigeration and air conditioning is a special refrigeration method based on the photovoltaic effect of solar energy, that is, through the "light-electricity-cold" approach, and using the electricity generated by solar cells to drive semiconductor refrigeration devices to achieve heat energy transfer. The electricity converted by solar photovoltaics can not only match the DC power supply mode of thermoelectric refrigeration, but also the solar radiation intensity and the cooling demand have a good time matching. In addition, solar energy is clean and environmentally friendly, with abundant resources, inexhaustible, and solar energy and semiconductors are environmentally friendly. Therefore, solar semiconductor refrigeration and air conditioning can create a high-quality green living space. This design uses Hainan's unique natural conditions and takes low cost as the benchmark to provide a design method for a solar semiconductor refrigeration and air conditioning test device. This method has broad application prospects in Hainan and tropical areas. One of the tasks of this project is to design a solar semiconductor air conditioning control system.

1 System composition of solar semiconductor air conditioner

The solar semiconductor refrigeration system can be composed of five parts: solar photovoltaic conversion device, energy matching digital controller, energy storage device, semiconductor refrigeration device, and system control device.

When the sun is shining, the solar photovoltaic converter can convert the sunlight energy shining on it into electrical energy, providing the necessary energy source for the air conditioning system. The electrical energy output by the solar photovoltaic converter in this article is very consistent with the electrical energy required by the air conditioning system. When there is no sunshine or insufficient sunshine, other auxiliary energy sources or energy storage devices are required to store part of the electrical energy output by the solar photovoltaic converter for backup, thereby ensuring that the solar semiconductor air conditioning system can operate around the clock. The digital control matcher can match the output impedance of the solar cell array with the equivalent load impedance, so that the energy transmission and conversion of the entire system is always in the best state, and at the same time control the overcharge and over-discharge of the energy storage device.

Semiconductor cooling and heating devices are usually composed of multiple thermopiles or refrigeration units, in which both the cold end and the hot end are equipped with heat dissipation devices. When cooling is required, the cold end is placed indoors to absorb heat to achieve the purpose of lowering the temperature and cooling; the hot end is placed outdoors for ventilation and heat dissipation. In winter, when the ambient temperature is low and heating is required, the direction of the current passing through the thermopile can be changed by changing the positive and negative poles of the power supply. At this time, the cold end of the thermopile becomes the hot end to release heat to the room, and the original hot end becomes the cold end to absorb heat to the surrounding environment, thereby achieving the purpose of heating and air conditioning. Figure 1 shows the experimental device diagram of the refrigeration module of this design.

The control device of this system has two main functions. One is to adjust the indoor temperature and measure and control the temperature of the surface of the heat-conducting ceramic plate at the cold end and hot end of the refrigeration plate. The other is to adjust the indoor humidity, that is, to control a humidification device. This system can not only realize automation and intelligence, but also provide the most comfortable environment indoors. The overall system test device is shown in Figure 2.

2 Design of air conditioning control system

In semiconductor refrigeration and heating devices, the surface of the thermally conductive ceramic sheet at the cold end and the hot end of the refrigeration sheet is coated with thermal grease to reduce the contact thermal resistance. However, the thermal grease will easily melt when it exceeds 60°C. In this way, it is necessary to keep track of the temperature of the ceramic surface at all times. Once this temperature is exceeded, the fan needs to be turned on for heat dissipation. In addition, the room temperature is set within a certain range (-10°C to 40°C). Users can adjust the temperature according to their own requirements with an accuracy of ±0.5°C. In addition, the system can also detect indoor humidity and automatically adjust the humidity based on the comparison between the actual humidity and the set value. The human-computer dialogue interface is mainly used to set the upper and lower limits of temperature and humidity and to display the temperature and humidity values ​​in real time.

3 Hardware Design

This system uses the AT89C51 single-chip microcomputer produced by ATMEL, two DS18B20 integrated temperature sensors produced by DALLAS, and capacitive humidity sensor HS1101 for hardware design. The system is divided into five parts: humidity acquisition, temperature acquisition, keyboard display, alarm display, and execution output. Each circuit is based on the AT89C51 single-chip microcomputer, and the temperature, humidity or keyboard scanning signals are collected to the single-chip microcomputer by the single-chip microcomputer input/output port. After the single-chip microcomputer's calculation processing, the input and output ports are output to the alarm display and execution ports for automatic control and monitoring of temperature and humidity. The control system structure block diagram is shown in Figure 3.

3.1 Temperature Collection

The PO.1 and P0.2 ports of the microcontroller are used as the data input and output ports of the temperature sensor. The temperature sensor DS18B20 uses a one-wire data transmission, so this system only needs one port to complete the input and output operations of the sensor. After the temperature sensor detects the analog temperature, it can be converted into a 9-12-bit digital value and stored in the register. When reading the temperature value, it can be read from port PC5 under strict timing.

3.2 Humidity Collection

HSll01 is actually equivalent to a humidity-sensitive capacitor, and its oscillation circuit is composed of a 555 timer. When the ambient humidity changes, the capacitance of the humidity sensor HSll01 will change accordingly. In this way, the capacitance value can be converted into a square wave signal with a frequency inversely proportional to it through the oscillation circuit, and the signal is transmitted to the microcontroller through PD3. The microcontroller can obtain the corresponding humidity value through frequency calculation.

3.3 Keyboard Display

CH452L is a keyboard display driver chip, whose pins DIN, DOUT, LOAD, and DCLK are connected to PB0~PB2 and PD2 of the microcontroller respectively. The system can set various parameters through the keyboard. The temperature and humidity values ​​collected by the microcontroller can also be displayed in real time through the digital tube.

3.4 Output Execution Port

The system can automatically detect the temperature and humidity values, and determine whether the temperature and humidity values ​​exceed the limit range. If they exceed the range, PEO and PE1 will output signals to control the actuator to adjust the temperature and humidity. In order to improve the stability of the system, a photoelectric isolator should be used between the single-chip system and the actuator unit to isolate the system from the on-site environment.

4 Software Design

After the microcontroller is powered on, the system should be initialized first. After the initialization is completed, it is determined whether the upper and lower limits of temperature and humidity are set. If they are set, it enters the parameter setting subroutine, otherwise, it enters the temperature and humidity detection subroutine. After the temperature and humidity detection subroutine is called, it enters the temperature and humidity parameter display subroutine, and then makes an over-limit judgment. If there is an over-limit, it enters the alarm display and execution subroutine, otherwise, it returns to the initialization module and re-executes. The main program execution flow chart is shown in Figure 4.

The main program of this design includes initialization module, temperature and humidity detection module, temperature and humidity parameter display module, alarm display module and execution module. The initialization module is responsible for calling the initialization system subroutine to initialize the relevant IO terminals and timing counters; the temperature and humidity detection module is responsible for calling the temperature detection subroutine and the humidity detection subroutine. The temperature detection program starts the temperature conversion from the initialization of the temperature sensor DS18B20. After the conversion is completed, it reads the 9-bit binary code and processing data and converts it into the corresponding temperature value; the humidity detection program starts to calculate the frequency of the humidity signal from the initialization of the humidity sensor HS1101 and converts it into the corresponding humidity value; the temperature and humidity parameter display module is mainly responsible for calling the display parameter subroutine of the keyboard display driver chip CH452L. The CH452L display driver can start the display driver from the initialization of CH452L, enter the display program, and send the temperature and humidity values ​​at the same time; the execution module is responsible for calling the alarm display and execution subroutines. The execution program and the alarm display program start from judging whether it is over-limit. As long as any parameter of the temperature and humidity exceeds the limit, the system will enter the control execution program and the alarm display program.

5 Conclusion

Solar semiconductor air conditioners have the advantages of energy saving and no noise, which can meet the common needs of mankind. The solar semiconductor air conditioner control system introduced in this article uses temperature and humidity sensors and takes the single chip as the core. Therefore, the temperature and humidity monitoring system has a high cost performance, is simple to use, and works stably and reliably. In fact, this control system can be used not only in air conditioners, but also in greenhouses, grain storage and other temperature control aspects, so it has a certain promotion value. The test results also show that the system can detect the indoor temperature well and can automatically adjust according to the set temperature, and can automatically cut off the power when the temperature is over-temperature. The response is very sensitive and can achieve the expected purpose.