Application design of Delta ES2 series CPU and PLC in solar water heating system
Abstract: Saving energy, protecting the environment, developing and using clean, environmentally friendly renewable energy, optimizing the energy structure, and developing a low-carbon economy are important ways for my country to achieve sustainable development. With its abundant reserves, safety and reliability, clean and pollution-free advantages, solar energy has become one of the important choices for countries around the world to respond to energy crises, environmental degradation, and achieve sustainable development. Using Delta PLC to control the solar water heating system can realize system automation, improve system operation stability, and reduce operating costs. This system has strong practicability, low installation and operation cost, and strong promotion.
1 IntroductionThis system has a wide range of applications and is suitable for occasions that require hot water supply, such as office buildings, hotel baths, etc., and is especially suitable for areas with abundant solar energy resources. The control system adopts Delta DVP40ES2 PLC, DVP04PT-E2, DVP04AD-E2, and Delta human-machine interface HMI B07S515. The system has stable working performance and high degree of automation, especially the constant temperature water outlet design saves a lot of water resources. The design of heat collection cycle makes solar hot water efficiently circulate into the water tank, and the addition of auxiliary heat sources solves the weather conditions of insufficient solar resources. Hot water supply under.
2 system configurationDelta series man-machine interface, Delta ES2 series CPU, Delta PT-E2 series temperature control module, Delta AD-E2 series analog to digital module, solar collector, electric heating wire (or air source heat pump, etc.) Auxiliary heat source), heat preservation water tank, bath control pump, heat collection circulation pump, solenoid valve, temperature sensor, liquid level sensor, power transmitter, etc., as shown in Figure 1.
Figure 1 System frame diagram
3 System working principle and cycle process(1) Automatic water supply
A liquid level sensor p is installed in the water tank. When the water in the water tank is lower than a certain value (20%), the automatic water replenishment valve is powered on, and the water tank is automatically refilled. When the water level reaches the set value (90%), the automatic water replenishment valve is powered off and the automatic water replenishment stops. .
(2) Heat collection cycle
When the water temperature at the outlet of the collector (the temperature sensor is installed at the outlet) is higher than the water temperature in the water tank and reaches the PLC setting start temperature difference (6-10 degrees Celsius), the collector circulation pump starts; the low temperature water in the hot water tank enters In the evacuated tube collector group, the relatively high temperature water in the collector is circulated to the hot water tank, which increases the temperature of the water in the water tank. When the temperature difference drops to the system setting stop temperature difference (1-3 degrees Celsius), the circulation pump stops and the heat collection cycle stops. This is repeated, and the heat is gradually transferred to the water tank, so that the temperature of the water in the water tank is gradually increased until it reaches the temperature required for bathing.
(3) Constant temperature water outlet in pipeline
The constant temperature return water pipeline circulation is mainly for the indoor hot water pipeline. In order to ensure that there is hot water as soon as the nozzle valve is opened during bathing, and at the same time to reduce the waste of ineffective cold water, the hot water return pipeline must be installed and pipeline circulation measures must be taken. . The pipeline circulation adopts a constant temperature circulation method, and a temperature detection sensor and a circulation pump are installed in an appropriate position in the indoor hot water return pipeline, and a temperature range is set to control the operation of the pump. When the water temperature in the pipeline is lower than the set value, the bathing pipeline circulation pump is started, and the low-temperature hot water in the pipeline is pumped into the insulation water tank. When the water temperature reaches the set value, the pipeline circulation pump stops running.
(4) Constant temperature control
When the water temperature in the water tank is lower than a certain value, the collector cannot reach the temperature of the bathing hot water. At this time, turn on the electric heating or other auxiliary heat sources (air source heat pump) in the water tank to ensure that there is The essential gas for hot water supply.
(5) Antifreeze cycle in winter
Outdoor pipes (between the heat preservation water tank and the heat collector) may be frozen in the cold winter, so it must have an antifreeze cycle function; when the temperature of the heat collector (detection sensor temperature) is lower than a certain value (2-5 degrees Celsius), Start the heat-collecting circulation pump to pump the hot water in the heat preservation water tank into the heat collector to prevent the pipeline from freezing.
4 Electrical control system designThe upper computer of the system selects HMI b7s515 type touch screen to realize the visual monitoring and control of system operation. The lower computer selects Delta series PLC, the host CPU selects DVP40ES2, the temperature module selects 04PT-E2, and the AD module selects 04AD-E2. The expansion module can also add a power transmitter to monitor the power of solenoid valves, circulating pumps and auxiliary heat sources, as shown in Figure 2.
Figure 2 Schematic diagram of the system hardware framework
(1) The temperature-related signals measured by the temperature sensor are converted into digital quantities by the PT module and then transmitted back to the PLC's CPU. The status of the PLC is reflected on the touch screen to realize real-time monitoring of data, as shown in Figure 3.
Figure 3 External wiring diagram of temperature sensor PT100 and DVP04PT module
(2) After the electric signal is measured by the water tank liquid level sensor, the electric signal is converted into a 4-20mA standard current signal by the liquid level transmitter, and then converted into a digital signal by the AD module and sent back to the PLC, which is based on the set value Make a judgment and control the opening and closing of the solenoid valve of the water tank, as shown in Figure 4.
Figure 4 The external wiring diagram of the level transmitter and 04AD-E2 module
In addition, the measured temperature of each temperature sensor directly represents the temperature of each component, so as to control the operation of the system. Therefore, the installation location of the temperature sensor is extremely important. The water temperature where the temperature sensor is installed must be able to represent the average temperature of the measured part.
5 Electrical control system software development(1) WPL Soft develops PLC control program
WPL Soft is the program programming software used by Delta's DVP series of programmable controllers in the Windows system environment. Delta PLC uses a memory that can be programmed to perform logical operations, sequential operations, timing, and counting. And arithmetic operations, and can control various types of machinery or production processes through digital or analog input and output.
The key to system control is the comparison of temperature and liquid level, which can be easily realized through the comparison command of PLC.
The frequency and accuracy of reading parameters of each expansion module are the key to this control system. The temperature control module and AD conversion module provided by Delta PLC can easily realize the automatic and precise control of the system.
(2) Touch screen human-machine interface (HMI) program
The touch screen replaces part of the mouse and keyboard functions. The input device installed in the front of the display screen is the medium and dialogue interface for transferring and exchanging information between people and the control system, including remote information transmission and control, and is an important part of the control system . Add the switch quantity in the PLC control program and associate it with the register of the HMI to realize the association between the HMI and the PLC, as shown in Figure 5.
Figure 5 PLC program controls the start and stop of the heat-collecting circulating pump
6 ConclusionThis application realizes the automatic control and monitoring of the hot water system through Delta PLC and its touch screen. The addition of an auxiliary heat source solves the shortcoming of single solar energy that is greatly affected by weather conditions (if the auxiliary heat source is selected as an air source heat pump, the system is more Electric heating has significant advantages of low power consumption, safety, comfort, environmental protection, and low carbon).
In the control system, multiple parameters such as temperature, liquid level, and power are added, which are reflected on the touch screen to realize the visual monitoring of important parameters of the operating system. Allows users to have a clear grasp of many parameters such as the water temperature in the water tank, the temperature of hot water in the bath, the amount of water in the water tank, and the power consumption of the system. The actual system is stable in operation, convenient in maintenance, and highly scalable. It is especially suitable for hot water supply in hotel baths, office buildings and other occasions. In addition, according to the requirements of indoor heating in winter, hot water at an appropriate temperature can be automatically controlled to enter the heating pipe to realize a hot water control system compatible with bathing and heating, as shown in the attached table.
Attached table: Comparison table between this system and ordinary solar water heating system
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