Design of Intelligent Building Automatic Control System Based on Fieldbus C-CLINK and PLC

In recent years, various high-rise buildings have been continuously built in many cities, and the various types of equipment in the buildings are widely distributed. Operating costs are the most concerned by the owners, so many large buildings have designed building intelligent systems to centrally manage the equipment in the building.Building Automatic Control System (BAS) is essentially the application of modern computer distributed control systems in modern multi-functional buildings. It controls various equipment in the building, such as power distribution equipment, water supply and drainage equipment, and HVAC equipment at their respective sites. Under control

In recent years, various high-rise buildings have been continuously built in many cities, and the various types of equipment in the buildings are widely distributed. Operating costs are the most concerned by the owners, so many large buildings have designed building intelligent systems to centrally manage the equipment in the building. Building Automatic Control System (BAS) is essentially the application of modern computer distributed control systems in modern multi-functional buildings. It controls various equipment in the building, such as power distribution equipment, water supply and drainage equipment, and HVAC equipment at their respective sites. Under the control of the device, the various systems are coordinated with each other according to the predetermined control strategy, working in the best state, and achieving the effect of energy saving and comfort. The BA system usually has 1 to 2 central control master stations. The central master station can monitor the operation status and important operating parameters of each controlled device, and record the historical trend of the operation status and the cumulative operation time of the equipment, the type and number of alarms. And so on, to provide a reliable basis for equipment management analysis and maintenance plans. At present, many well-known foreign companies such as American HOneywell, JOHNOSOH and Siemens have launched some specialized building intelligent control systems.

Although these systems have strong functions, the system investment is relatively large. In view of the characteristics of the building control system, we adopt a distributed control system based on Mitsubishi fieldbus C-CLINK technology and a programmable logic controller (PLC). It has the characteristics of reliable operation, simple modification of control software, and low cost. The central station The Kingview software developed by Yakong Automation Software Technology Co., Ltd. is a configuration software running on Windows 95/NT. With multitasking, multithreading and good real-time performance, it has been used in many engineering fields such as electric power, refrigeration, chemical industry, machinery manufacturing, and traffic management to construct effective monitoring and data acquisition systems. The entire control system has been successfully applied in the new plant of Zhejiang Printing Factory. Practice has proved that the system has stable and flexible performance and is very suitable for use in some small and medium-scale intelligent building automation systems.

2. System hardware composition:

(1) Introduction to CC-Link

CC-Link is the abbreviation of CONTROL&COMMUNICATION LINK. It provides a communication rate of 156KBPS to 10MBPS (depending on the communication distance of the system) through a simple three-core shielded cable, and the maximum communication distance can reach 1200M (156KBPS rate). Various modules (including digital I/O and analog I/O) and sub-station controllers that can be linked to the CC-Link network can easily form various types of control systems and greatly simplify the control system wiring.

(2) Introduction to Mitsubishi FX2n Series Programmable Controller

Mitsubishi FX2n series programmable controller has small size, fast running instruction speed (0.08us/basic instruction), built-in 8K step RAM and clock, PID operation instruction, it is the highest performance in the FX series, and has analog control and system Various special-purpose components of communication are a set of PLC that can meet diversified and wide-ranging needs. This series of PLC has a strong communication function. It can be directly connected to the CC-Link network through the FX2n-CCL communication module to form a distributed control system. The data can be exchanged with the master station through the CC-Link network, and the whole The system conducts centralized management, monitoring and control.

(3) The block diagram of the entire system is shown in the figure:

Design of Intelligent Building Automatic Control System Based on Fieldbus C-CLINK and PLC

3. System function and control strategy

(1) Power supply and distribution system:

Safe and reliable power supply is a prerequisite for the normal operation of intelligent buildings. The system converts voltage, current, power factor and frequency sensors into 4-20ma signals and sends them to the on-site controller’s A/D conversion module to read into the controller as needed to realize energy management. For example, the power distribution system uses advanced microcomputers to detect air circuit breakers and can provide RS232 or RS485 communication interfaces and communication protocols. A dedicated PLC module can be used to replace the A/D converter to obtain power data to improve accuracy and real-time performance and reduce costs. The system can also detect the switch status of important circuits and the temperature rise of the transformer, and monitor various abnormal conditions.

(2) Air-conditioning subsystem

The air-conditioning system consumes the most energy in buildings, accounting for about 45%. The building automation system minimizes energy consumption while ensuring a comfortable environment. According to the climatic conditions of Hangzhou with variable seasons and long periods of time during the freezing summer, an intelligent operation console composed of PLC and LCD touch screen was designed in the refrigerating machine room. This operation console eliminates other instrument panels and makes the panel standardization and miniaturization. , Saving wiring. The operator can intuitively monitor the relevant parameters in the building such as the temperature of each sampling point, outdoor temperature and humidity, and the water level of each pool through the operation console of the refrigerating machine room to provide the operator with information, and can also provide information for the operator when the climate is not suitable for automatic control operations, such as changing seasons Switch to manual operation from time to time or during equipment maintenance, and you can also set the relevant parameters of each equipment through this console to make the equipment run in the best state.

This system is composed of three parts: refrigeration unit, heat exchanger and air-conditioning system terminal equipment:

Control strategy and function

A. According to the operation requirements of the refrigerating unit, the starting and stopping sequence of the cooling water pump, air conditioning water circulating pump, cooling tower fan and refrigerating unit is fully automatic, semi-automatic and manual for logical control.

B. Calculate the real-time system cooling or heating capacity based on the temperature difference between the supply and return water temperature of the air conditioner and the water flow rate of the air conditioner, and Display the system load rate in real time, providing a basis for the semi-automatic or fully automatic start-stop and number control of refrigeration units and heat exchangers.

C. This system adjusts the bypass valve to achieve a constant flow rate of the water system by detecting the pressure difference between the supply and return water pressure of the air conditioner and comparing it with the set value for PID calculation.

D. By detecting the temperature of the cooling water, the start and stop of the cooling fan and the number of units are controlled to ensure that the refrigerant pressure of the chiller is within a certain range, and the purpose of energy saving can be achieved.

E. The end of the air conditioning system is composed of air conditioners and scattered fan coils. The air conditioner is applied for on-site or controlled by the time program, and the PID algorithm is used to control the opening of the water valve of the air conditioner according to the room temperature required by the process requirements of the printing workshop; the operating time of the air conditioner unit can be set according to the seasonal program. It can also realize the accumulative running time of the air conditioner; the air filter silt alarm; the night air change and antifreeze operation and other functions.

F. Measure the cold or heat consumed by the air conditioners in each workshop. The calculation formula for cold or heat is E=△t * Q, where △t is the temperature difference between the supply and return water of the air conditioner, and Q is the cumulative value of the air conditioner’s flow. Considering the high cost of the flow sensor, we use a large-caliber pulse water meter to measure the flow. The measurement error is less than 5% at normal flow, which can meet the accuracy requirements of factory cost accounting.

G. During winter operation, the number of units is controlled according to the winter program, and the heat exchanger steam valve is linked with the air-conditioning water pump, and the rest of the functions are the same as in summer.

(3) Boiler and water supply and drainage control subsystem:

This subsystem monitors the operation of the boiler, controls the auxiliary equipment of the boiler, monitors the water level of the living water tank, fire water tank, and sump, alarms for high and low water levels; detects the water intake, and automatically controls the corresponding water pump according to the set value The start-stop control can also be remotely controlled by the BA center or manually on site.

Design of Intelligent Building Automatic Control System Based on Fieldbus C-CLINK and PLC

Control strategies and functions

A. This system monitors the operating parameters of the oil-fired boiler, such as steam pressure, temperature, boiler water level, flue temperature, etc.; auxiliary equipment for the boiler system includes: feedwater pump, deaerator pump, oil pump, daily fuel tank oil level And temperature, the oil level of the big fuel tank, the temperature, the water level of each water tank, etc. are all monitored through the on-site intelligent console, and the operating parameters can also be set through the console.

B. The continuous change of the liquid level of each water tank is dynamically displayed on the BA center screen, and the corresponding water pump is controlled according to the water level of the living water tank.

C. Control the start and stop of the sewage pump according to the water level of the sewage pond. It is displayed on the on-site monitoring station and the main station, and the status/fault of the sewage pump and the start/stop of the water pump are judged through the software.

D. The daily and monthly water consumption of the factory is measured according to the pulse water meter, which can be used as a basis for energy consumption by the building management system to detect abnormal water consumption in time.

E. Provide the accumulated operating time and equipment status of the equipment of the water supply and drainage system, and formulate equipment maintenance and repair plans and pool cleaning plans.

(4) Lighting control subsystem:

The lighting system has a wide range of points and is second only to the air conditioning system in intelligent buildings. It is of great significance to effectively control and save energy.

Control strategies and functions

A. Public lighting is automatically switched on and off according to time. During the off time, you can manually apply to turn on the lights.

B. Holiday and flood lighting can be switched on and off at any time, or they can be switched off manually after turning on the lights.

C. It can be linked with the security service system. When the security system detects an illegal intrusion, the corresponding area lighting is turned on to facilitate the camera and grasp the situation of the intruder.

Fourth, the system software part

Due to the large number of control points in the building control system, in order to improve the efficiency of programming, it is important to formulate the use of PLC internal components in detail. We have developed the following PLC internal parameter table (partial) according to the actual controlled equipment

2F PLC 32CCL Set station number (Station No:) 13~16 occupy 4 stations

Master station RWr (slave station to master station) address range: 310H~31FH, 16 points in total

Master station RWw (master station to slave station) address range: 210H~21FH, a total of 16 points

Master RX (slave to master) address range: F8H~FFH, a total of 112 points

Master station RY (master station to slave station) address range: 178H~17FH, a total of 112 points

According to the above detailed internal parameter table and functional requirements, you can draw the ladder diagram to compile the PLC program, and at the same time, the data dictionary of the central station Kingview monitoring software is developed, and the animation connection is carried out according to the type and characteristics of the data to achieve real-time monitoring of the equipment. And control.

Applying the feature of flexible expansion points of the CC-Link fieldbus system, the system can also use pulse watt-hour meters and pulse hot water meters to measure the electricity and the air conditioning capacity of the fan coil in the building according to the needs, which can be achieved at a lower cost. Satisfactory accuracy greatly improves the level of intelligent building management.

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