The primary network is the management layer network, which can actually be the building’s computer network system or a dedicated local area network (LAN) built exclusively for BAS.
The secondary network is the building’s monitoring layer network.
First-level: Central Workstation
Installed in the control center.
Second-level: Universal Gateways and Routers
Installed in each low-voltage shaft.
Third-level: Direct Digital Controllers (DDCs), Sensors for Collecting Field Signals, and Actuators for Driving Field Control Devices
Installed locally alongside the controlled equipment.
It adopts TCP/IP network transmission with a data transmission rate of not less than 100 Mbps.
This layer can connect servers, operator stations, BAS network controllers, Ethernet routers, and interface routers.
Its core functions are to centrally manage the building’s electromechanical equipment and monitor their operation status. It transmits large volumes of data to the network server within the shortest time to complete data acquisition tasks promptly, enabling the server to calculate optimal control parameters based on data statistics and ensure reliable communication connections and fast response speeds.
The main intelligent building equipment operating on this network includes:
Building Management Server: Installed in the control center.
Building Management Workstation: Can be located anywhere on the network.
Network Controllers: Deployed at control sites, low-voltage shafts, etc.
Building Management Clients (Browsers): Accessible from any location on the network.
It adopts advanced and comprehensive Ethernet technology and complies with the BACnet IP standard protocol.
The adoption of BACnet technology is driven by its inherent advantages. A large number of VAV (Variable Air Volume) systems are used in this project, which are characterized by adaptability to the flexible and variable needs of modern office applications.
BACnet networks feature excellent openness, enabling seamless connection between BACnet devices from different manufacturers. Therefore, using a BACnet network to construct the monitoring layer network of this project ensures maximum system flexibility, making the system easy to expand, modify, and maintain, and providing great convenience and possibilities for future system upgrades and maintenance.
All equipment controllers and Direct Digital Controllers (DDCs) in the control layer communicate point-to-point via the control layer network, independent of upper-layer equipment and networks.
The network can connect real-time field controllers, intelligent communication interfaces, intelligent instruments, BACnet frequency converters, etc. DDCs can independently implement on-site control and regulation functions.
The two-level networks are connected via Network Controllers (NCs).
NCs feature high reliability support, independent CPUs, and large-capacity memory, equipped with independent embedded operating systems to provide efficient real-time data processing capabilities.
The overall system is a distributed intelligent system. Each network controller can independently manage at least 1,500 hardware points. In the event of a network controller failure, all on-site DDC controllers can continue to operate normally independently.
In addition, network controllers support devices using protocols other than BACnet IP, including but not limited to open protocols such as BACnet MS/TP, LonWorks, Modbus, and other proprietary protocols, maximizing the compatibility and scalability of the entire system.
Network controllers have sufficiently powerful hardware and software performance and achieve hardware-software decoupling, meaning that data, programs, and other content in the network controller are stored independently of the controller hardware. In case of hardware damage to the network controller, all stored data and programs remain unaffected, and the problem can be solved directly by replacing the hardware device.
The on-site Direct Digital Controllers (DDCs) adopt Ethernet controllers, complying with the BACnet IP standard protocol and meeting the BACnet B-AAC standard.
The controllers shall have built-in points, including at least 4 different types of points, and the number of points per field controller shall be no less than 21 points to facilitate independent control of on-site equipment.
For complex working conditions, the field controllers shall support I/O point expansion as required, with the maximum expandable points (excluding the DDC’s own points) being no less than 128 points. The expansion modules and DDC controllers shall be products of the same brand.
Since Modbus RTU is a widely adopted bus protocol for current field devices, the on-site DDCs can directly connect to standard Modbus RTU devices for communication and ensure support for at least 128 Modbus points.
Monitoring of fresh air and return air temperature and humidity;
Monitoring of supply air temperature and humidity (available on some devices);
Monitoring of fan operation status, manual/automatic status and fault status;
Monitoring of air filter "clogging" status and alarm;
Detection of CO₂, PM2.5, VOC and formaldehyde concentrations in return air;
Monitoring of fan differential pressure alarm;
Monitoring of supply air duct static pressure (available on some devices);
Fan frequency regulation control and frequency feedback monitoring (available on some devices);
Adjusting the opening degrees of fresh air dampers and return air dampers by comparing the return air CO₂ concentration with the set value to save energy;
Both startup and shutdown of fans are controlled by preset time programs;
Monitoring of outdoor temperature and humidity.
Startup sequence: Open fresh air/return air dampers → Start the fan → Confirm fan operation → Adjust air conditioning water valves.
Shutdown sequence: Stop the fan → Close fresh air/return air dampers → Close air conditioning water valves.
When the monitored air quality is below the adjustable set value, the fresh air damper is maintained at the minimum adjustable opening degree;
When the monitored air quality is above the adjustable set value, the fresh air damper is opened to the maximum adjustable opening degree;
The sum of the opening degrees of the return air damper and the fresh air damper is 100%.
Winter mode:
If the return air temperature is below the adjustable set value, the hot water valve moves toward full opening and the chilled water valve is fully closed;
If the return air temperature is above the adjustable set value, the hot water valve moves toward full closing and the chilled water valve is fully closed.
Summer mode:
If the return air temperature is below the adjustable set value, the chilled water valve moves toward full closing and the hot water valve is fully closed;
If the return air temperature is above the adjustable set value, the chilled water valve moves toward full opening and the hot water valve is fully closed.
Transition season mode: Both the chilled water valve and hot water valve are fully closed.
Filter Alarm: Differential pressure switches are installed on both sides of the primary filter. When the filter is clogged and the primary differential pressure exceeds the set value, an alarm is automatically triggered to remind cleaning or replacement of the filter.
Fan Fault Alarm: When the fan experiences overcurrent or short circuit, the protection device sends an alarm signal.
Fan Differential Pressure Alarm: The differential pressure across the fan is monitored, and an alarm is generated when the differential pressure exceeds the limit.
Alarm Function: When any of the above faults occur, an automatic alarm is triggered to remind relevant personnel for maintenance. Each point of the unit is reported in a list, with alarm display and other functions.
Supply air temperature and pressure monitoring: Only for monitoring supply air temperature and pressure.
Return air temperature, and return air CO₂, PM2.5, VOC, formaldehyde concentrations.
Operation status: Operation status of the supply fan.
Monitoring of supply air temperature and humidity;
Monitoring of fan operation status, manual/automatic status and fault status;
Monitoring of air filter "clogging" status and alarm;
Monitoring of PM2.5 concentration in air ducts, and outdoor PM2.5 concentration (available on some devices);
Monitoring of supply air duct static pressure (available on some devices);
Fan frequency regulation control and frequency feedback monitoring (available on some devices);
Adjusting the opening degree of the electric two-way valve by comparing the measured supply air temperature with the set temperature;
Manually adjusting the opening degree of the fresh air damper according to the number of indoor personnel to save energy;
Both startup and shutdown of the fan are controlled by preset time programs.
Supply Fan Interlock Control: The fresh air damper, electric water valve, and humidifier are interlocked with the supply fan. Monitor the manual/automatic, operation, fault signals, and frequency feedback signals in the supply fan power distribution cabinet to control the startup and shutdown of the supply fan.
- Startup sequence: Open fresh air damper → Start the fan → Confirm fan operation → Turn on the humidifier and electric water valve according to temperature and humidity sensors and seasonal mode;
- Shutdown sequence: Reverse of the startup sequence.
Fan On/Off Control: The fan is started during working hours according to the "time schedule" function, with no fault alarm or anti-freezing alarm status.
Water Valve Regulation Control & Supply Air Temperature Control: When the unit is in operation, the control logic varies by season:
- Winter mode: If the supply air temperature is below the adjustable set value, the hot water valve moves toward full opening and the chilled water valve is fully closed; if the supply air temperature is above the adjustable set value, the hot water valve moves toward full closing and the chilled water valve is fully closed.
- Summer mode: If the supply air temperature is below the adjustable set value, the chilled water valve moves toward full closing and the hot water valve is fully closed; if the supply air temperature is above the adjustable set value, the chilled water valve moves toward full opening and the hot water valve is fully closed.
- Transition season mode: Both the chilled water valve and hot water valve are fully closed.
Supply Air Humidity Control: When the unit is in operation, the monitored supply air humidity is compared with the adjustable set humidity. If the monitored supply air humidity is below the adjustable set value, the humidifier is turned on; if it is above the adjustable set value, the humidifier is turned off.
Graphic Display: After the system is started, color graphics are used to display different states and alarms, showing the value of each parameter and the cumulative operation time of the air conditioning fan. The set value can be arbitrarily modified with a mouse to achieve the optimal working condition.
Filter Alarm: Differential pressure switches are installed on both sides of the primary filter. When the filter is clogged and the primary differential pressure exceeds the set value, an alarm is automatically triggered to remind cleaning or replacement of the filter.
Fan Differential Pressure Alarm: The differential pressure across the fan is monitored, and an alarm is generated when the differential pressure exceeds the limit.
Fan Fault Alarm: When the fan experiences overcurrent or short circuit, the protection device sends an alarm signal.
Alarm Function: When any of the above faults occur, an automatic alarm is triggered to remind relevant personnel for maintenance. Each point of the unit is reported in a list, with alarm display and other functions.
Supply air temperature and pressure.
PM2.5 concentration.
Operation status: Operation status of the supply fan.
Both startup and shutdown of the fans are controlled by preset time programs;
Monitoring of fan operation status, manual/automatic status and fault status;
Monitoring of indoor temperature in equipment rooms with high heat generation and ventilation requirements, such as power transformation and distribution rooms;
CO concentration monitoring points are installed in the underground garage to implement garage air quality control.
Fan Start/Stop Monitoring: Normally controlled by BAS, the fan is started during working hours according to the "time schedule" function with no fault alarm; the fan power supply is cut off when a fire alarm is triggered.
Carbon Monoxide Monitoring: When the CO concentration is above the adjustable set value, the fan starts automatically; when the CO concentration is below the adjustable set value, the fan turns off automatically.
Equipment Room Control: For equipment rooms with high heat generation and ventilation requirements such as power transformation and distribution rooms, adjust the fan start/stop, number of operating units and rotation speed according to the usage of heat-generating equipment or indoor temperature.
Supply Fan Frequency Control: Manual frequency conversion can be performed in the central control room.
Monitoring: Monitor the manual/automatic, operation and fault signals of the circuits in the power distribution cabinets of normal fans and fire-fighting cum normal fans.
Graphic Display: After the system is started, color graphics are used to display different states and alarms, showing the value of each parameter and the cumulative operation time of the fan. The set value can be arbitrarily modified with a mouse to achieve the optimal working condition.
Fan Fault Alarm: When the fan experiences overcurrent or short circuit, the protection device sends an alarm signal.
Alarm Function: When any of the above faults occur, an automatic alarm is triggered to remind relevant personnel for maintenance. Each point of the unit is reported in a list, with alarm display and other functions.
Indoor carbon monoxide concentration;
Operation status: Operation status of the fan.
Monitoring of operation status, manual/automatic status and fault status of domestic water pumps;
Monitoring of overflow and low liquid level of domestic water storage tanks;
Monitoring of operation status, manual/automatic status and fault status of sewage pumps;
Monitoring of overflow and low liquid level of sump wells.
Monitoring: Monitor the manual/automatic, operation status and fault alarm signals of drainage pumps and domestic water pumps;
Graphic Display: After the system is started, color graphics are used to display different states and alarms, showing the value of each parameter and the cumulative operation time of the water pump. The set value can be arbitrarily modified with a mouse to achieve the optimal working condition.
Automatic Water Level Alarm for Sump Wells and Domestic Water Tanks: An alarm signal is sent when the water level exceeds the set alarm line.
Water Pump Fault Alarm: When the water pump experiences overcurrent or short circuit, the protection device sends an alarm signal.
Alarm Function: When any of the above faults occur, an automatic alarm is triggered to remind relevant personnel for maintenance. Each point of the unit is reported in a list, with alarm display and other functions.
