1. Introduction In intelligent buildings, the goal of building automation systems is to create a safe, convenient, and comfortable indoor environment, enabling people to work, study, and live in a good mental state. Simultaneously, through building automation systems, building owners achieve comprehensive automatic control of air conditioning, power supply and lighting, water supply and drainage, fire protection and alarm systems, security systems, background music systems, and more, ensuring the entire building operates efficiently, energy-saving, and under optimal conditions. Within and between these systems, a centralized computer management and distributed control approach is typically adopted. Distributed computer control, using multiple computer control devices (basic controllers) distributed at the controlled equipment locations, completes the real-time monitoring, protection, and control tasks of the controlled equipment, overcoming the limitations of centralized computer control (highly concentrated risks) and the single function of conventional instrument control. A central management computer installed in the central control room, equipped with strong digital communication, CRT display, and rich control management software, performs centralized operation, display, alarm, data analysis, and optimization control functions, avoiding the disadvantages of conventional instrument control, such as difficult human-machine interaction and lack of unified management. However, due to economic, technological, and historical reasons, each subsystem has become an "automation island." One solution is to transform it, upgrading it into a distributed control system (also known as a distributed control system) while protecting the original system's hardware and software resources. This article discusses some related issues. 2 System Hierarchy Building distributed control systems can be divided into field control level, substation monitoring level, and central management level according to functional layering, as shown in Figure 1. It connects each level and between levels through a computer network to form a complete distributed control system. The functions and characteristics of each level are briefly discussed below. 2.1 Field Control Level The field control level consists of field direct digital controllers (DDCs) and field communication networks (fieldbus). A DDC is a control device that integrates strong and weak current, with a relatively simple industrial control computer as its core and various low-voltage control electrical appliances, sensors, actuators, etc. It is used to directly control each controlled device and can communicate with the central control computer. A fieldbus is a communication network between various DDCs and between them and the upper-level computer. It generally uses standard industrial serial communication standards, such as conventional RS-485 or CANbus fieldbus interfaces, and uses inexpensive shielded twisted-pair cable as the transmission medium. Depending on the fieldbus network structure, the field control level can be configured in star, tree, or bus topologies. The characteristics of the field control level are mainly reflected in: multiple information systems, bidirectional multivariate communication, high reliability and accuracy, system self-diagnostic functions, convenient maintenance and repair, interoperability, low cost, and low installation cost. The main functions of the field control level are: acquiring process data, converting data, outputting control commands, performing direct digital control, completing data communication with substations, and monitoring and diagnosing field-controlled equipment. 2.2 Substation Monitoring Level The substation monitoring level is the upper-level monitoring and management level of the field level, composed of I/O cards. It transmits process information to upper and lower levels through a communication network. Its characteristics are as follows: high reliability, strong real-time performance, more flexible control, high communication speed, and large information capacity. The substation monitoring level is a crucial component of the building automation system. Its performance significantly impacts the real-time nature of information, the quality of control, and the accuracy of management decisions. Its main functions include: data acquisition, data conversion and processing, data monitoring and storage, continuous, batch, or sequential control calculations and output control, data and equipment self-diagnosis, and data communication. 2.3 The central management level, centered on the central control room operator station and supplemented by external equipment such as printers and alarm devices, serves as the human-machine interface. Its main characteristics include: using multimedia technologies such as screen prompts, sound, images, pictures, and curves to display the controlled building processes and output data; large data storage capacity and large display information volume; convenient and simple operation; alarm and fault diagnosis capabilities; optimized control; coordination of control among substations; printing and tabulation; and data communication. Its main functions include: data recording, display, storage, and printing; coordinated optimization, coordination, and maintenance; alarm and event handling and diagnosis; data communication; optimized control; and management and scheduling of the entire building automation system. 3. Basic Components of a Building Distributed Control System Although there are many types of building distributed control systems, from a system structure analysis, they consist of three main parts: distributed process control devices, centralized operation and management, and a communication system—a high-speed data channel. The distributed process control devices, equivalent to the field control level and substation monitoring level, consist of multi-loop controllers, single-loop controllers, multi-function controllers, programmable logic controllers, and data acquisition and processing devices. The centralized operation and management section consists of a central operation station, a central management computer, and external devices such as printers and plotters, providing a human-machine interface. Data communication between each level and between the computer and the microprocessor within each level is achieved through the communication system. The relationship between the three parts is shown in Figure 2. 3.1 Distributed Process Control Units Distributed process control units serve as the interface between the distributed system and the controlled process. They possess the following characteristics: adaptability to harsh environments; distributed control, implementing decentralized control of geographically dispersed process units, separating monitoring and control, and dispersing hazards to improve system reliability; real-time performance, with a fast clock frequency and sufficient word length in hardware, and real-time and multi-tasking operations in software; and independence, exhibiting strong independence compared to the overall building automation system, continuing to operate normally even in the event of communication failures or equipment malfunctions at the higher level. 3.2 Centralized Operation and Management Units The main function of the centralized operation and management unit is to centralize information from each distributed process unit, and through monitoring and operation, issue operating commands to each distributed control unit. The collected information is used for analysis, research, printing, and storage, serving as the basis for management, planning, and scheduling. Its main characteristics are: large information capacity, ease of operation, and good fault tolerance. While distributed automation systems typically consist of three basic components, each with its own characteristics depending on the manufacturer, they share common structural features. The most common structure is: distributed process control stations + local area network (LAN) + integrated information management system. LAN technology enhances the system's communication and networking capabilities. Through fieldbus, the system can communicate and operate with intelligent instruments and controllers in the field. Structurally, it is an open and interoperable system, representing the mainstream structure for building automation systems in current intelligent buildings. 3.3 Network Topology In distributed systems, the communication network is mostly a LAN, with topologies including bus, star, and ring. Furthermore, to accommodate system expansion requirements, communication networks of the same or different types can form various network structures. 4 Intelligent Distributed Building Automation Systems As mentioned earlier, distributed building automation systems are superior to centralized building automation systems in terms of functionality and reliability, and are widely used in equipment automation in intelligent buildings. However, they also have some shortcomings, the most prominent being limitations in openness and interconnectivity, making the configuration of building automation systems less flexible. In intelligent buildings, the devices requiring monitoring are not only diverse but also vary greatly in characteristics. Using only one type of distributed building automation system (DBA) product often cannot meet the control requirements of all devices. Therefore, it is frequently necessary to select DBA products from different manufacturers as individual DBA systems and combine them to form a unified building equipment automation system. This necessitates interconnection between different DBA systems. Currently, DBA systems from different manufacturers cannot directly interconnect, meaning their openness is relatively poor, thus limiting their application in building automation systems. With the development of computer communication technology and large-scale integrated circuit technology, some foreign manufacturers have introduced a new type of automation system: the intelligent distributed monitoring system. The core of the intelligent distributed system is a communication and control microprocessor made using very large-scale integrated circuit technology. Also known as a neuron chip (integrating three CPUs and corresponding memory, I/O interfaces, etc.), its communication and control functions are equivalent to an industrial PC. Using this chip as the basic control point of the distributed network not only enables communication and control but also allows for the integration of controlled devices distributed across the field, thereby achieving more ideal distributed control. The intelligent distributed building equipment automation system has the following characteristics: (1) The neuron chip, which serves as the basic control node, has strong communication capabilities and the network communication protocol is embedded in it. Therefore, the interconnection between nodes is very convenient and can form an open "monitoring bus". Various sensors and actuators of different devices can be directly "hung" on the bus, which is convenient for expansion and has good openness. Through programmable intelligent nodes, or by embedding the neuron chip into products from different manufacturers, these products can be easily connected directly to the same system to achieve interconnection. (2) Various transmission media and ordinary twisted pair, coaxial cable, optical cable, wireless radio frequency, infrared, and even power lines can be used for signal transmission to form a control network. (3) Programming is simple and changes in system layout do not require major changes to the application program. Therefore, development is convenient and the system development cycle is short. (4) The intelligent distributed system is a masterless distributed control mode. The failure of a control node only affects the connected devices and will not cause the paralysis of the entire system or subsystem. Even if the central control computer fails or goes offline, the entire system still completes the monitoring task of the equipment according to the program embedded in each node. Therefore, the overall reliability of the system is high. 5. Conclusion Intelligent buildings contain numerous building devices with varying operational characteristics and monitoring requirements. Typically, the entire building equipment monitoring system is divided into several subsystems based on equipment type, characteristics, and requirements. Smaller subsystems with fewer monitoring points can utilize a central control unit or operator station to form a distributed control system. Larger subsystems with numerous monitoring points can have individual intelligent terminals connected via a local area network (LAN) to form a building automation system. While offering significant flexibility in software implementation, the best choice is Wonderware's Factory Suite component system. Regardless of the existing system's type (distributed or programmable logic control), it allows access to the Wonderware software data platform via an I/O server. This platform provides powerful tools for building, testing, running, and verifying applications. Its software boasts strong functionality, excellent compatibility and scalability, and is easy to develop and use. It is being widely promoted and has been proven by engineering practice to be a wise choice.