Control of air conditioning system in bas of a uni

2022-08-15
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The control of air conditioning system in bas of a university teaching building

Abstract: through the introduction of the control of air conditioning system in building automation system, this paper expounds the content and method of controlling air conditioning system. Keywords: building automation system combined air conditioning unit fresh air unit forced draft fan freezing station heat exchange station Untitled Document overview a university teaching building is a landmark building in the national university campus. The building area is about 70000 square meters, and the total height is nearly 100 meters. There are three floors underground and twenty-seven floors above the ground. At the same time, the lower room of the building is equipment room and parking lot; The group buildings are large laboratories and graduate classrooms, multimedia classrooms and multi-function halls, activity halls, international conference halls and small and medium-sized conference rooms; The main building is for office use. The building will be built into a real high-tech, intelligent weak current system. Its BAS system is designed by Metasys building management system of Johnson company in the United States. Here is a detailed introduction to the control of the air conditioning system in this system. 1. Overview of this building (BAS) according to the use characteristics and design requirements of this building, the requirements of building equipment automation management (BAS) for experimenters are not high. The system should monitor, control, record and alarm the air conditioning unit, ventilation unit and refrigeration station system; Monitor, record and alarm the main parameters of the power supply system; Detection and alarm of elevator, detection of ponding pit and control of sewage pump; The lighting system is monitored and managed to achieve the purpose of comfort, convenience, energy saving and easy management. The system is mainly composed of one operation station, one network controller and 24 DDC controllers. As shown in the following schematic diagram: operation station network controller

this system can connect the central operation station and the nodes of the network controller through Ethernet (N1). At the same time, the direct digital controller (DDC) installed everywhere in the building will be connected to the network controller through RS485 fieldbus (N2) to maintain close contact with the direct digital controller and the central operation station on other network controllers. Sensors and actuators are connected to the above direct digital controllers (DDC). 2. (BAS) control of air conditioning system the air conditioning system in this building mainly includes the following equipment: (1) 26 combined air conditioning units, (2) 31 fresh air units; 38 forced draft fans; (3) 1 refrigeration station system; 2.1 monitoring of air conditioning units there are 26 combined air conditioning units in the whole building. Among them, there are 8 sets on the first floor, 7 sets on the second floor, 3 sets on the third floor, 8 sets on the fourth floor and 3 sets on the fifth floor. The air conditioning unit is a comfortable air conditioning unit, which provides comfortable and high-quality air for meeting rooms, offices and classrooms. The air treatment method is as follows: the outdoor fresh air is regulated by the fresh air valve, and then sent through the primary effect filter and return air mixing preheating section, surface cooling heating section, and high-efficiency filter of the blower. The contents to be monitored are as follows: return air duct return air temperature (AI) fan operation monitoring (DI) fan fault alarm signal (DI) automatic or manual status display (DI) fan start and stop control (do) fresh air damper control (AO) two-way water valve control (AO) indoor temperature (AI) indoor humidity (AI) indoor static pressure difference (AI) on the operation station, each air conditioner will be displayed by color three-dimensional graphics compared with the previous group, Intuitively show the operation status and alarm signals of different air conditioning units, dynamically display the operation status, fault status and return air temperature of each unit, and at the same time, each air conditioning unit carries out timed start and stop control, and can modify the set value or the opening degree of end equipment through the mouse, and change the start and stop status of equipment, so as to achieve the best working environment. These air conditioning units are monitored and controlled by Metasys system according to the pre arranged time of each day, including holiday procedures. 2.1.1 control of the water valve and fresh air valve of the air conditioning unit. The control of the water valve is mainly to adjust the opening of the cold and hot water valve according to the feedback temperature signal of the return air temperature sensor, so that the supply air temperature tends to the set temperature (PI proportional adjustment); When the return air temperature is higher than the set temperature, DDC automatically outputs the off signal to close the hot and cold water valve, otherwise, it opens the hot and cold water valve, so as to meet the setting requirements of indoor temperature, prevent the inconvenience caused by too high and too low temperature to people's work, and save energy to the greatest extent. According to general experience, the opening degree of the valve before installing the regulating valve is generally about 85%. After installing the regulating valve for regulation, the opening degree of the valve is only 40% - 60%, so energy consumption can be reduced. The regulation and control of fresh air valve is mainly used in the following three aspects: (1) energy saving. Adjusting the fresh air valve can ensure the maximum use of fresh air. When the fresh air temperature is close to the indoor temperature, all fresh air valves are opened; When the temperature difference between the fresh air temperature and the set temperature is too large, it is only necessary to ensure the minimum fresh air volume, turn the fresh air valve to the minimum position, and maximize the use of return air. (2) Protect the fan. Due to the local air quality, the fresh air valve is normally open, and the filtration is easy to be dirty, so it needs to be cleaned frequently. Therefore, it is necessary to realize the interlock between the fresh air valve and the fan to lubricate the friction part of the machinery. When the fan is closed, the damper will automatically close to prevent dust from entering. (3) There are multiple indoor static pressure difference sensors in the room on each floor, which can detect the static pressure difference between the indoor and the external environment, and determine the opening degree of the damper according to the comparison between the static pressure difference and the set value, so as to make the room in the best working and learning environment. 2.2 monitoring of fresh air units there are 31 fresh air units in the whole building, including one on the lower second floor, one on the lower first floor, one on the first, second and fourth floors, two on the third floor, four on the fifth floor, and one on each floor from the seventh to the twenty sixth floors, which mainly provide high-quality fresh air for the rooms. The air treatment method is: the outdoor fresh air is sent to the rooms on each floor after passing through the fresh air valve, the primary effect filter, the surface cooling heating section and the blower. The monitoring contents are as follows: supply air duct supply air temperature (AI) fan operation monitoring (DI) fan fault alarm signal (DI) fan automatic or manual status display (DI) fan start and stop control (do) fresh air damper control (do) two-way water valve control (AO) fresh air temperature (AI) supply air temperature (AI) on the operation station, each fresh air unit will be visually displayed through color three-dimensional graphics

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