Depair AHU field devices now communicate over Modbus RTU

Temperature and pressure sensors, modulating dampers and fans: the field devices of Depair AHUs are now accessible over Modbus RTU. They integrate directly into another building automation system.

What it enables

The building controller reads measurements and operating states, whatever its manufacturer. It also sends setpoints to the dampers and fans. All devices share a single RS‑485 bus instead of one cable per signal.

What travels on the bus

Each device exposes its own data points:

• Temperature and pressure sensors: the measured value;
• Modulating dampers: the opening setpoint and the damper status;
• Fans: the speed setpoint and the operating status.

One bus, daisy-chained

The devices are daisy-chained on a single RS‑485 pair. Each has its own Modbus address: the building controller, as bus master, polls them in turn. A termination resistor closes the bus at each end.

There are fewer conductors to pull and label, and fewer terminals in the panel. An additional device connects to the existing bus.

Who it is for

BMS integrators, consulting engineers and facility teams who already run their own automation. The AHU fits into the existing installation without imposing its own controls.

Your BMS uses BACnet/IP or Modbus TCP? A standard gateway converts from the Modbus RTU bus.

With Depair controls

Nothing changes. When the AHU ships with its Depair controls, BMS integration takes place at the controller level, as described on the Controls page.

Commissioning

At commissioning, the integrator sets the baud rate and the address of each device on the controller. The register table gives each point’s address, unit and access, read or write.

Security

Modbus RTU provides neither authentication nor encryption. The bus therefore stays local: it links the devices to the building controller, with no direct access from outside.

Documentation

The Modbus register table is available on request.