Design And Realization Of Central Air Conditioning System Based On BACNet

In recent years, the popularity of central air-conditioning is growing rapidly. The system design of the traditional central air-conditioning generally use load estimation method and the design is based on the maximum load of the central air-conditioning. Besides, the operation mode of the water system and fan coil management system both apply to constant flow and constant air volume. So the energy consumption of the central air conditioning system is extremely huge and the building operation costs are very high.Based on the data analysis of the non-central air conditioning units, currently the output power is far greater than the actual environmental load the during the90%of the running time of the central air-conditioning system, which contributes to the great energy loss. According to the survey of China’s construction energy consumption, the energy consumption of the central air-conditioning normally accounts for40%to60%of the total energy consumption of large public buildings. So, it is very necessary for the central air conditioning to improve its cooling, heating and ventilation energy-saving according to its demand.For the problem of large energy consumption of air conditioning system, this article describes a thermostatic energy saving control system based on BACnet (building automation control network data communication protocol). The system combines WSN network distribution detection technology and every executive node collects the flow of people, humidity, air quality and other environmental variables data real-time. The host computer does the data collection and analysis and builds the temperature distribution field. The combination of the parameters of the distribution field can adjust the compressor power、fan speed and steering using coordination inverter technology and make each fan coil work together to achieve the variable air volume、 frequency conversion、 sentinel directional cooling and heating effect according to needs, thus matching the output power of central air-conditioning with the actual load. In addition, in order to better control the temperature, this article also uses fuzzy PID algorithm which helps to obtain the exact values of the output of the pulse width modulation. The rotational speed of the fan motor can be changed through changing the duty cycle of the pulse width modulation, thus changing the temperature finally.In addition, the new interface standard based on BACnet protocol can make the seamless connection of the electrical interface come true deeply between air-conditioning systems and other building control equipments, thus reaching the various building equipment control linkage and the integrated energy saving purpose. The system achieve access to the internet through the gateway node and sends each node status information to the control center and accept the control information from the remote control center.Firstly, this paper introduces the key technologies of the central air-conditioning control system based on BACNet protocols. Secondly, explains the BACNet protocol、 WSN network distribution detection technology and fuzzy PID control algorithm. Then, introduces the overall scheme and workflow of the control system and describes the sub-modules respectively from the hardware design and software design. At last, the system was tested by building experimental platform to simulate the experimental environment and the test results were verified.