In recent years, with the continuous development of automatic control technology and the continuous decline of hardware costs, computer automation has more applications in the field of HVAC. Properly applying the self-control technology to the control and management of HVAC systems can effectively improve the system operation quality, save operating energy consumption, improve management level, reduce operational labor intensity, and achieve good economic and social benefits. Based on the construction practice of the Shanghai Songjiang University City Foreign Trade College project, this paper describes the application of automatic control technology in the central air conditioning system. This article refers to the address: http:// The project is the administrative building of Shanghai Institute of Foreign Trade, with a construction area of ​​10,000 square meters and a total of 4 floors. The air conditioning and ventilation system basically adopts the air conditioning mode of the fan coil and the fresh air. The new fan group is set in the air conditioner room of each floor. The fan coil is concealed and horizontal, with 130 units and 4 new fans. The air duct system is a low pressure system. The whole system includes: ducted axial flow fan, air handler, fan coil, muffler louver, fire damper and exhaust valve, air distributor, various side air supply and return air, Diffusers, etc. The self-control of central air-conditioning systems is mainly divided into the following three aspects: 1. Comprehensive adjustment and control of cold and heat sources and water pipe systems At present, the host system has a microprocessor-based unit controller that provides control of the inlet and outlet temperatures of the evaporator and condenser, the inlet and outlet pressure of the water flow switch compressor, and the temperature. 1. The unit adopts the group control scheme to complete the automatic interlock control of the heat pump, and complete the monitoring, query and alarm of the target. When the unit is in normal operation, the system accumulates the running time. When the unit fails, it can display and alarm in the main controller in time. 2. The system obtains the temperature, pressure and flow value of the cold water supply and return water through the RS232 interface, calculates the total cooling load and the circulating water volume of the whole building, and automatically adjusts the chilled water bypass valve according to the total supply of chilled water and the pressure difference of the return water. Ensure the stability of the pressure inside the pipe. 3. Change the set value of the system according to the working time schedule. For example, during the daytime office hours, the set value is different from the nighttime no-management period. 4. Start and stop the compressor according to the command, adjust the compressor inlet guide vane valve according to the outlet setting value of the freezer room, and set the chilled water outlet temperature. Water temperature sensors, flow sensors, etc. are installed to monitor the operating status of these hosts. The collection and control of monitoring point information is implemented by a microprocessor system (DDC controller). The system is a system composed of a microprocessor, a RAM, a ROM, etc., and can collect various information of the monitored points to complete the control task. 5. The chilled water system is composed of a chilled water circulation pump connected to the freezer evaporator through the piping system and various cold water equipment (air conditioner and fan coil) of the user. The monitoring task of the automatic control system is to ensure that the evaporator of the freezer passes enough water to make the evaporator work normally and prevent freezing; to provide sufficient water quantity to the users of the chilled water to meet the requirements of use, and to meet the requirements of use as much as possible. Reduce the power consumption of circulating water pumps, etc. Second, the measurement of basic parameters of fresh air and air conditioning units, start and stop control of equipment 1. In the central air-conditioning system, in order to improve indoor comfort, air freshness, cleanliness, etc., it is necessary to add a proper amount of fresh air, and the fresh air volume accounts for a large proportion of the air-conditioning heat and cold load. The building has 4 new wind turbines, each of which must guarantee fresh air requirements at this level. 1) Install a temperature and humidity sensor on the air duct of the fresh air air conditioning unit and the air supply duct in the typical area, and adjust the flow rate of the unit coil water flow and humidification method to make the temperature meet the requirements, and the air cooler of each fresh air and air conditioning unit. The electric regulating valve and the actuator on the coil and the humidifying steam pipe are controlled by a nearby controller to realize one-to-one distributed control; 2) The system calculates the temperature and humidity load according to the indoor temperature and humidity value, automatically determines the gear position of the fan speed, and controls the air volume to meet the indoor and outdoor comfort requirements. When the unit is working, according to the indoor and outdoor temperature and humidity and the set temperature and humidity, the opening of the fresh air valve is determined, and the opening of the exhaust valve and the bypass valve is controlled to achieve energy-saving operation. When the unit stops working, the fresh air valve and the exhaust valve Keep closed and the return air valve remains fully open; 3) Monitor the operating status of the fan, record the running time of the fan, and have the function of local and remote control and automatic control of the start and stop of the fan. 2. The air water heat exchanger is connected to the cold water in the summer to cool and dehumidify the fresh air, and the hot water is heated in the winter to heat the air. The dry steam humidifier humidifies the fresh air during the winter. Therefore, the on-site DDC controller has to perform the following functions: 1) Start and stop new fans as required. According to the fresh air temperature, the PID adjusts the water valve, keeps the supply air temperature as the set value, and controls the dry steam humidification valve so that the relative temperature of the outlet air of the winter fan reaches the set value; 2) Monitor the working status and fault status of the new fan. Measure the air temperature and humidity parameters of the fan outlet and make it meet the control requirements. Measure the pressure difference between the two sides of the fresh air filter. When it reaches a certain value, a filter clogging alarm is generated and an alarm is displayed; 3) In winter, when the temperature after the hot coil is lower than a certain set value, the antifreeze protector operates, the controller will stop the fan operation and close the fresh air damper, and open the hot water valve to 100% to prevent The coil is cracked and alarmed. Third, the monitoring and control of the fan coil 1. In the central air conditioning system, in addition to the new fan unit and air conditioning unit, the heating and cooling equipment also uses a large number of fan coils. Its function is similar to that of an air conditioning unit, but it is much simpler. 2. At present, there are two kinds of controllers on the market, one is that the coil controller is DDC control, and has the function of communicating with the host. This controller can be controlled centrally and can be adjusted for cold water and cold, but it is more expensive and not used much. The other is a coil controller that does not have a communication function. The fan coil can be divided into several groups according to the connection of the water system. A flow meter, a return water differential pressure transmitter, and a return water temperature sensor are installed at the branch entrance of each group. This building uses the latter control. Of course, the automatic control of the central air-conditioning system can not be completely controlled by the DDC. When the final system commissions the air volume and the cooling effect, the automatic control cannot automatically adjust the size of each damper to achieve the design requirements. We generally use the “reference air vent method†to manually adjust the air volume. Before the air volume adjustment of the system, the air volume of all the air outlets is initially measured, and the ratio of the initial air volume to the design air volume after each air outlet is calculated. After comparing the air outlets, the air outlet with the smallest ratio is found, and the air outlet with the smallest ratio is used as the reference. The tuyere is adjusted by the tuyere. Nowadays, the central air-conditioning of many buildings is only at the maximum load for several days in a year, and the central air-conditioning cooling load is always in a dynamic state. Most central air conditioners are driven by the system with most of the maximum cooling load for maximum power. In this way, the contradiction between the actual need of the cold load and the maximum power output is caused, resulting in huge energy waste, causing huge electricity expenses to the user and increasing the cost of the operator. Therefore, the central air-conditioning automatic control system with energy saving, good control performance, fast control rate and convenient centralized management will have more room for development in future projects. Auto Identify Technology - The LENCENT multi usb plug charger would identify the connected devices intelligently and provide optimized charging universal compatibility. 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