Building automation management subsystem (BAS) building automation management subsystem is the core of weak current system of intelligent engineering building. Its high reliability is the cornerstone of high reliability of the whole weak current system. Therefore, BAS system adopts three-level control mode. The operation station level is composed of computer and printer. It adopts real-time graphic monitoring operation software and is the man-machine interface of BAS system. It can not only observe the operation status and data of the current or previous system and various electromechanical equipment monitored by displaying or printing various information, but also change the operation of various electromechanical equipment through the operation of keyboard or mouse, So as to meet the specific monitoring requirements.

1、 Network controller level
Network controller is not only an important device of BAS system communication network, but also the heart of the whole BAS system. On the one hand, it communicates with the operation station and other network controllers through Ethernet, on the other hand, it communicates with the direct digital controllers distributed throughout the building through fieldbus network. All information of the whole system is stored in the network controller. The network controller has a variety of control functions, such as operation time statistics of various electromechanical equipment, event statistics, peak shaving and load limiting calculation of power load, linkage control, unit group control and other complex high-performance control functions, which systematically monitors the whole BAS system. At the same time, the network controller is an important interface for connecting each subsystem to the BAS system for facility integration.

2、 Field controller level
The field controller constitutes the third level of the system. Its main function is to receive the data sent by various sensors and detectors installed on various electromechanical equipment, carry out corresponding calculations (such as PID, maximum value, delay, etc.) according to the preset parameters and pre prepared control program in the controller, and control various electromechanical equipment, At the same time, adjust parameters or start relevant programs according to various instructions sent by the operation station through the network controller at any time to change or start the monitoring of corresponding equipment.

3、 The characteristics of three-level control are as follows:
The three-level control of the system adopts the structure of decentralized control and centralized management. Even if a part of the control or line of the system network is damaged, only this part of the system is paralyzed and will not affect the operation of the whole system. At the same time, the field controller adopts industrial devices and has independent operation function. Even if the operation station or network fails to work in case of problems, the field controller can still continue to operate according to the preset parameters and pre prepared control program in the controller, and the whole system can still operate. The three-level control structure is adopted to make the structure of each layer relatively simple and reduce the complexity of maintenance. At the same time, the primary network is 10 megaethernet and the secondary network is 9600 baud RS-485 bus, which reduces the possibility of interference between system networks, especially the field environment. The building automation management subsystem monitors all mechanical and electrical equipment in the building, such as cold and heat source units, air conditioning units, fresh air units, VAV terminal devices, water supply and drainage, air supply and exhaust, power transformation and distribution, lighting, elevators and other equipment.

4、 Cold and heat source unit:
Modern cold and heat sources are generally chillers and heat pumps, equipped with a variety of water pumps, cooling towers, butterfly valves, water level switches, thermometers, flow meters, etc.

The cold and heat source system is the heart of the HVAC system in the building. It is also a large energy consumer and has high control requirements. Its general monitoring contents are as follows: unit operation parameters: including the start and stop status of the unit, fault alarm, supply and return water temperature, flow, start and stop status of each water pump and fault alarm. Remote measurement and control of differential pressure of main water supply and return pipe. Switch on and off the unit, water pump, cooling tower, butterfly valve, etc. according to the given time procedure. Determine the number of units to be started according to the cooling / heating load, and implement unit group control. Air conditioning unit:

Unit operation parameters: including return / supply air temperature, humidity, filter blockage status, fan operation status and overload alarm. Start and stop the fan according to the given time procedure. Adjust the water valve opening of the air conditioner according to the temperature. The water valve is interlocked with the fan. Fresh air unit: unit operation parameters: including inlet and outlet temperature, filter blockage status, fan operation status and overload alarm. Start and stop the fan according to the given time procedure. Adjust the opening of water valve of fresh air fan according to the temperature. VAV terminal device: monitor the temperature and air volume of the terminal device. Start and stop the fan according to the given time procedure. Controls the damper baffle angle of the end device. Water supply and drainage monitoring: monitor the high and low liquid levels and alarms of various water tanks. Monitor the operation status and overload alarm of various water pumps.

Control the start and stop of the water pump according to the parameter requirements. Supply / exhaust fan monitoring: monitor the operation status and overload alarm of supply / exhaust fan. Control the start and stop of the fan according to the time program. Power transformation and distribution monitoring: monitor high / low voltage electrical parameters, including voltage, current, frequency, active power, reactive power, power factor, etc. Monitor the operation status and fault alarm of the contactor in the switch cabinet. Monitor transformer temperature and fault alarm. Lighting monitoring: monitor the operation status of each lighting circuit. Control the opening and closing of the main contactor of the selected circuit according to the time program. Elevator monitoring: monitor the operation status and fault alarm of each elevator.