Design Of Embedded Control System For Central Air Conditioning

With the development of the society and living standards, people show more demands on both living and office environment. Thus, lots of concepts emerge, such as Intelligent Building, Smart Planet, Internet of Things. During all these systems which help to improve our living condition greatly, Intelligent Building deserves more discussions. Intelligent Building adds hommization and technology to traditional buildings, and its key point is the optimal combination of monitoring system, warning system, intercom system, access control system, conference system. Thanks to all these systems, the buildings become safer, more convenient, more efficient, and more energy-efficient. Central air conditioning system, enriches the concept of Intelligent Building, promotes buildings’intelligent, plays an important role in temperature regulation, and does good to energy saving.Central air conditioning system improves both office and living condition, but also causes lots of energy consumption. There are still some problems in central air conditioning system, and the problems mainly caused by the decentralized control method which can hardly realize intelligent management. In office buildings, as well as government buildings, the energy waste is considerable which caused by staff’s forgetting to turn off the switch of central air condition system. Some central air conditioning manufactures tried to add network to the control system, but the communication methods are mainly confined to RS485or I2C so that there are many defects in such systems such as the limit of communication distance and the capacity of terminals. At the same time, because the controller is mainly8051or its enhanced series in traditional control system, the function of the control system is restricted.With the development of INTERNET, people become interested in connecting various devices to an exciting network such as Ethernet. This demand helps to produce many compact TCP/IP protocol stack, such as uIP and LWIP, which should be a gospel to some low-end processors. uIP, which is programmed by C language, makes the protocol stack transplanting progress simpler. The code size as well as demand for RAM is very little, which makes the low-end processor with low performance has the access to INTERNET. With the development of uIP, its safety, reliability, real time performance has been further improved, so that it becomes possible that making INTERNET applied to central air conditional system. At the same time, it emergences lots of powerful controller which has high speed, low power consumption, and large storage capacity, such as enhanced51series designed by STC and STM32series designed by ST. Therefore, it is possible to design a low cost but powerful central air conditional system.Based on the analysis above, this paper aims at the research and development of an modern central air conditional system with remote monitoring function, which makes the usage of INTERNET possible. The purpose of the system is to connect the monitoring software and terminals by Ethernet, so that the control center can monitor every terminal. The whole control system realizes centralized control by Ethernet, and it realizes the centralized management, energy saving, and high efficiency.The control system adopts hierarchical network. The first layer is PC equipped with monitoring software whose function is to monitor the system, print statements, and calculate charge. The monitoring software is programmed by visual c++6.0and SQL Sever2000. The second layer is middle station, which is embedded uIP and has the access to Ethernet, and it is based on STM32F103VET6and ENC28J60. The third layer is repeater, which is based on STC12C5A16S2which has two UARTs. One UART is connected with middle station, and the other is connected with terminals. The forth layer, temperature controller which is also called terminal, is based on STC10F08XE. The terminal controls the temperature of the room, and communicates with repeater by RS-485.On the overview of current central air conditional system, this paper emphasizes the design scheme of the control system, the hardware and software structure, design method, schematic diagrams, as well as key control procedures. Finally, this paper summarizes the whole system objectively.