FGA anywAiR iO RTPU Auto Mode
Smart Temp SMT-770 integration with Rubix Compute 5 and Danfoss PAC control
Overview
This solution describes the configuration and operating logic used to integrate a Smart Temp SMT-770 wall controller with a Fujitsu rooftop packaged unit controlled by a Danfoss controller. A Rubix Compute 5 acts as the intermediary controller and processes the Modbus logic required for automatic heating, cooling, scheduling, after-hours operation and fault indication.
1. System components
| Component | Purpose |
|---|---|
| Rubix Compute 5 | Processes the control logic and communicates with the SMT-770 and Danfoss controller. |
| 4G router and SIM module | Provides authorised remote access for monitoring, programming and support. |
| Smart Temp SMT-770 | User interface for setpoint adjustment, mode selection, scheduling and after-hours override. |
| Danfoss PAC controller | Controls the rooftop packaged unit and supplies return-air temperature and fault information. |
| RS485 Modbus network | Provides serial communication between the three control devices. |
System architecture showing the Rubix Compute, SMT-770 and Danfoss controller network.
2. System operation
The user can operate the PAC unit from the SMT-770 wall controller. The controller is normally configured to show the setpoint only. The room temperature displayed by the SMT-770 is not used for system control; the operating temperature is taken from the wired return-air sensor connected to the Danfoss controller.
The SMT-770 provides the following functions:
- Change the temperature setpoint.
- Set a seven-day operating schedule.
- Select Off, Cooling, Heating or Auto mode.
- Start or cancel an after-hours override.
- Display an error indication when the Danfoss controller reports a fault.
3. Auto Mode operation
When Auto Mode is selected, the Rubix program compares the Danfoss return-air temperature against the setpoint entered on the SMT-770. The unit starts in ventilation mode and automatically changes between cooling and heating as required.
| Condition | System response |
|---|---|
| Return-air temperature is above Setpoint + Deadband | The unit enters Cooling Mode and remains in cooling until the temperature reaches setpoint. |
| Return-air temperature is below Setpoint - Deadband | The unit enters Heating Mode and remains in heating until the temperature reaches setpoint. |
| Return-air temperature is within the deadband | The compressors are disabled and the unit operates in Ventilation Mode. |
Cooling and heating compressor stages are controlled according to the temperature deviation from setpoint. In heating mode, the reversing valve remains energised until the unit is disabled or another operating mode is selected.
4. After-hours override
- Press the Override button on the SMT-770.
- The word Override appears on the controller display while the function is active.
- The PAC unit runs for the configured after-hours period.
- Press the Override button again to cancel the function before the timer expires.
The default after-hours duration is 120 minutes and can be adjusted by a technician.
5. SMT-770 programmable modes
| Mode | DIP switch setting | Functions |
|---|---|---|
| Residential | Switch 6 up, Switch 8 up | Basic unit control, setpoint adjustment and one schedule. |
| Commercial | Switch 6 up, Switch 8 down | Multiple schedules, after-hours operation and setpoint lockout. This is the default configuration. |
6. Default adjustable parameters
| Parameter | Default | Adjustment |
|---|---|---|
| Mode change delay | 0.5 minutes | Configured in the Rubix logic. |
| High setpoint limit | 30°C | User adjustable within the configured range. |
| Low setpoint limit | 18°C | User adjustable within the configured range. |
| Heating offset | 0.5°C | Technician adjustable. |
| Cooling offset | 0.5°C | Technician adjustable. |
| After-hours duration | 120 minutes | Technician adjustable. |
7. Modbus communication settings
| Device / network | Address / port | Baud rate | Parity |
|---|---|---|---|
| Serial network | RS485-1 or RS485-2 as configured | 9600 | None |
| Danfoss controller | 10 | 9600 | None |
| SMT-770 | 7 | 9600 | None |
Danfoss controller points
| Point | Register | Type | Use |
|---|---|---|---|
| Cool_Temp_Setpoint | 8621 | Int16 | Cooling setpoint written from the wall controller. |
| Heat_Temp_Setpoint | 8264 | Int16 | Heating setpoint written from the wall controller. |
| System_On_Off | 8398 | Int16 | 1 = On, 0 = Off. |
| On-Off Status | 16388 | Int16 | Read-only operating status. |
| System_heat_cool | 8400 | Int16 | 1 = Heating, 0 = Cooling. |
| RT_Temp | 21804 | Int16 | Return-air temperature used for system control. |
SMT-770 points
| Point | Register | Function |
|---|---|---|
| Thermostat Mode | 2 | 0 = Off, 2 = Heat, 3 = Cool, 4 = Auto. |
| Setpoint | 17 | User-entered temperature setpoint. |
| Fan_Mode | 3 | Read-only fan mode value. |
| Room_Temp | 322 | SMT-770 temperature value; not the default system control temperature. |
| Deadband | 40 | 0.5°C increments: 1 = 0.5°C, 2 = 1.0°C, 3 = 1.5°C. |
| Display_Mode | 24 | 0 = room and set temperature, 1 = set temperature only. |
| Heat Limit | 30 | Highest permitted heating setpoint. |
| Cool Limit | 31 | Lowest permitted cooling setpoint. |
8. Fault display
The Rubix Compute polls the Danfoss alarm registers over Modbus. When a Danfoss fault is detected, the SMT-770 displays Error on its LCD.
9. Rubix CE configuration
- Select the correct serial port in Rubix CE.
- Set the serial network to 9600 baud and no parity.
- Import the SMT-770 and Danfoss controller backups onto the Modbus network.
- Add a Flow Network node and select the correct MQTT topic.
- Deploy the node, load the approved Wires program and deploy the completed flow.
- Confirm that all required points are online and updating before testing the unit.
10. Functional testing
Complete the following checks after programming or replacing any controller:
- Confirm setpoint changes on the SMT-770 are reflected on the Danfoss display.
- Verify the setpoint cannot be reduced below 18°C or increased above 30°C.
- Test schedule ON and OFF operation and confirm the PAC fan starts and stops.
- Test Off, Cooling, Heating and Auto modes.
- In Auto Mode, test operation with the setpoint equal to, below and above the return-air temperature.
- Test after-hours override start and cancellation.
- Simulate a Danfoss fault and confirm that Error appears on the SMT-770.
- Clear the fault and confirm the Error indication is removed.
Summary
The anywAiR iO RTPU Auto Mode configuration provides automatic heating and cooling changeover, seven-day scheduling, after-hours operation, controlled setpoint limits and basic fault indication. Correct Modbus addressing, approved Rubix programming and complete functional testing are essential for reliable operation.