Abstract: With the development of the national economy, the demand for electricity has increased year by year. The current shortage of electricity supply in our country is widespread. In the economically developed coastal areas, there are often power cuts in industrial areas during the summer peak period. At the same time, in recent years, my country Energy conservation and environmental protection are vigorously advocated. With the improvement of people's quality of life, it is very important to improve the comfort, economy, and reliability of air conditioners. The use of advanced, practical and reliable programmable logic controller (PLC) for control is the mainstream of the current air conditioning control system. Aoyuexin 200 series high-performance small PLC, from CPU to expansion modules, explained its superiority in this field. Based on the insufficiency of the current central air-conditioning system control methods, the Aoyuexin 200 series controller is used to achieve effective control. The actual use shows that the program is reasonable and feasible, and the use effect is better than similar control products.
I. IntroductionAir conditioning is a special system for regulating the air in buildings. It controls the indoor temperature and humidity by turning on, off and continuously adjusting fans, valves, pumps and other equipment to meet certain requirements, thereby improving the comfort of the human body. With the continuous improvement of people's living standards, more and more large and medium-sized buildings adopt central air-conditioning systems to achieve cooling in summer and heating in winter, and to achieve economic and energy-saving purposes.
In order to improve the economy, reliability and maintainability of the air-conditioning system, it is necessary to use control products to control the various equipment of the air-conditioning system. Early central air-conditioning controllers were mostly on-site dedicated controllers, which had the disadvantages of simple control functions, difficulty in networking, and low information integration. With the development of computer technology, control technology and network technology, current central air-conditioning systems tend to use advanced, practical and reliable programmable logic controllers (PLC) for control. This article introduces an example of using Aoyuexin PLC products to control central air-conditioning.
The Aoyuexin 200 series programmable controller is applied to the air-conditioning system to realize networking and information integration, improve system reliability, reduce energy consumption, meet process requirements, ensure product quality, and improve the overall unit’s performance Cost-effective.
2. System introductionAn air-conditioning system is a ducted system. Compared with other central air-conditioning systems, the air-cooled ducted central air-conditioning system has the introduction of fresh air to improve the air quality, the temperature is more balanced, the noise is small, the adjustment is simple, the installation is simple, the operation is reliable, and the efficiency is Notable features such as high and low operating costs. The air duct central air-conditioning system uses air as the transport medium. Its principle is basically the same as that of a large all-air central air-conditioning system. It is a miniaturized all-air central air-conditioning system. It utilizes the outdoor host to centrally generate cold/heat, and the return air brought back from the room is cooled/heated, and then sent to the room to eliminate its air-conditioning cold/heat load. The air duct unit has a simple system, adopts a refrigeration cycle in which refrigerant and air directly evaporate and exchange heat, without intermediate heat transfer media, reducing losses and high efficiency. Due to the introduction of fresh air, the air quality can be greatly improved. The schematic diagram is shown below, in which the outdoor host adopts air cooling.
The system has the following characteristics:
In summer, the refrigeration unit runs to achieve cold regulation; in winter, the chiller is used together with the heat source to achieve winter heating. In the spring and autumn seasons, fresh air can be used to directly supply air to achieve energy-saving and comfortable effects.
Adopting the design method of centralized air conditioning, the air supply is large, the temperature difference of the air supply is small, and the room temperature is uniform. The air supply is diversified, and different air supply schemes can be formulated in specific situations to enhance the comfort of the human body.
Modular host is used to automatically adjust the cooling capacity according to the setting. Indoor and partition control, each indoor and independent operation, respectively adjust the air in each area.
Maintenance is very convenient. When the fault occurs, it will be displayed on the text display at the same time. The maintenance personnel can conveniently and quickly perform maintenance or repair according to the fault display.
It can be controlled individually or centrally, making the operation more economical and energy-saving.
Three, system controlThe control system adopts Aoyuexin 224C host series PLC, 200 series analog modules and 231 thermal resistance modules for expansion. 1. The OYES 200 series is fully compatible with Siemens S7-200 programming software. The original application program does not need to be modified. The 224C series CPU integrates two communication ports, one of which is a PPI communication port and the other is a free communication port (FPORT) with internal MODBUS. Protocol, 14DI/10DO altogether 24 digital quantity I/O, the program space is 24K, the data space is 10K, can be kept for three years after power-off, 4 5KHZ high-speed counters.
The air-conditioning application environment is relatively humid. Aoyuexin 200 series products have high reliability and can be treated with three preventions, which are suitable for various harsh environments.
Host system control requirements
1) Take corresponding control measures for loading, unloading and maintaining the system according to the current outlet water temperature and set value;
2) With fault detection and alarm functions, it can query current faults and historical fault records;
3) Timing control function, can automatically switch the unit;
4) The protection functions of the system and the press are complete.
3.3 Chilled water system control
The actual return water temperature is subtracted from the actual outlet water temperature and compared with the actual temperature difference for PID control. Logic control of the chilled water system: the PLC host first controls the chilled water outlet and return valve, delays 5 seconds to start the chilled water circulating pump, the chilled water pump is controlled by the inverter (the main circuit is separated, the inverter frequency signal is the same), the inverter frequency Controlled by the output current signal of the analog EM232 module. When the set temperature difference is greater than the actual temperature difference, it indicates that the actual cooling capacity is insufficient to meet the needs of the air-conditioned room, and the cooling capacity needs to be increased. The PLC controls the analog output current to increase, thereby increasing the refrigeration pump speed to increase the actual cooling capacity, then the actual temperature difference It will gradually decrease until it is close to the set temperature difference; when the set temperature difference is less than the actual temperature difference, it indicates that the actual cooling capacity is surplus and exceeds the needs of the air-conditioned room. The cooling capacity needs to be reduced, and the PLC control output current is reduced, thereby reducing the refrigeration pump speed In order to reduce the actual cooling capacity, the actual temperature difference will gradually decrease until it approaches the set temperature difference.
Concluding remarks:In the central air conditioner, the Aoyuexin 200 series programmable controller is used as the control hardware of the central air conditioner monitoring system, which greatly improves the comfort, economy, and reliability of the air conditioner, and reduces the cost of the air conditioner. The actual use of the plan shows that the plan is reasonable Feasible, the use effect is better than similar control products.
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