The Siemens BACnet ATEC (All-in-One Terminal Equipment Controller) is a high-performance DDC controller designed for Variable Air Volume (VAV) systems. It is widely used in commercial buildings, hospitals, schools, and data centers that require precise environmental control.
The controller integrates an actuator and a differential pressure sensor, supporting multiple VAV terminal applications such as cooling-only, cooling/heating, electric reheat, hot water reheat, and fan-powered units. Key advantages include:
Accurate PID control
Low power consumption
No calibration required
Suitable for pressure-independent airflow control
Typical scenario: In a cooling-only VAV system (Application No. 2860), commonly deployed in office buildings, the ATEC regulates airflow to maintain room temperature. By monitoring differential pressure, it achieves a balance between energy savings and occupant comfort.
Although ATEC supports BACnet MS/TP and can directly communicate with BAS, challenges remain in certain cases:
Compatibility issues with Modbus systems: Many EMS platforms support only Modbus TCP.
Cloud connectivity requirements: Lacks native MQTT support for direct cloud integration.
Multi-protocol complexity: BAS typically cannot handle MS/TP, Modbus TCP, and MQTT simultaneously.
A BACnet MSTP-to-Modbus TCP/MQTT gateway (e.g., BariumTech BL115P) resolves these issues by providing:
Protocol conversion: Translates BACnet MS/TP data into Modbus registers or MQTT messages.
Data aggregation: Multiple ATEC units can connect through a single gateway, reducing wiring complexity.
Remote configuration: Web-based mapping of datapoints, sampling intervals, and MQTT topics.
Physical Connection
Connect ATEC controllers to the gateway via RS-485 MS/TP bus.
Connect gateway to LAN via Ethernet or to the internet via 4G/5G.
Device Discovery & Datapoint Mapping
Gateway scans BACnet devices and identifies key objects:
Room temperature (AI)
Airflow setpoint (AO)
Damper position (AO)
Alarm status (BO)
Modbus TCP Mapping
Register 40001: Room temperature (×10, integer)
Register 40002: Airflow setpoint (CFM)
Register 40003: Damper position (0–100%)
MQTT Publishing
Data is published in JSON format, e.g.:
Topic structure: vav/atec/{device_id}/status
Security & Redundancy
TLS/SSL encrypted MQTT communication
Automatic reconnect & data buffering for reliability
Seamless integration: Existing Modbus systems can directly access ATEC data.
Cloud-ready: Easy connection to Alibaba Cloud, AWS IoT, ThingsBoard, etc.
Operational efficiency: Real-time monitoring, remote troubleshooting, reduced maintenance cost.
Energy optimization: Data-driven strategies improve system efficiency and reduce energy consumption.
In conclusion, Siemens BACnet ATEC plays a vital role in VAV systems. With a BACnet MSTP-to-Modbus TCP/MQTT gateway, multi-protocol integration and cloud connectivity become straightforward, enhancing building automation systems with greater intelligence and scalability. This solution is applicable to both retrofits and new installations.
