Alnor HRU-P
Controls Alnor HRU-P heat recovery ventilation units via Modbus RTU.
This template monitors and controls Alnor HRU-P heat recovery ventilation units via Modbus RTU at 115200 baud. It reads temperatures, fan speeds, airflow, humidity, CO2, filter status, and bypass position. It also provides write access for work mode selection, fan speed and airflow settings, bypass control, and GHE configuration.
- Protocol
- Modbus RTU
- Connection
- RS485, 115200 baud
- Registers
- 49, read and write
- Key readings
- Supply/Extract/Inlet/Exhaust temperatures · Supply and exhaust fan speed (%) · Supply and exhaust airflow (m3/h) · Indoor humidity and CO2 · Filter depletion and days left · Bypass position and status
- Available commands
- Work mode and turn on/off · Fan speed settings (Speed 1-3) · Fan flow settings (Speed 1-3) · Bypass and GHE control
- Compatible models
- HRU-SlimAIR-250-H-P · HRU-SlimAIR-250-H-CF-P · HRU-SlimAIR-250E-H-P · HRU-SlimAIR-250E-H-CF-P · HRU-SlimAIR-L-250-H-P · HRU-SlimAIR-L-250-H-CF-P · HRU-SlimAIR-L-250E-H-P · HRU-SlimAIR-L-250E-H-CF-P · HRU-SlimAIR-350-H-P · HRU-SlimAIR-350-H-CF-P · HRU-SlimAIR-350E-H-P · HRU-SlimAIR-350E-H-CF-P · HRU-SlimAIR-400-H-P · HRU-SlimAIR-400-H-CF-P · HRU-SlimAIR-400E-H-P · HRU-SlimAIR-400E-H-CF-P · HRU-SlimAIR-300-H-P · HRU-SlimAIR-300-H-CF-P · HRU-SlimAIR-300E-H-P · HRU-SlimAIR-300E-H-CF-P · HRU-SlimAIR-500-H-P · HRU-SlimAIR-500-H-CF-P · HRU-SlimAIR-500E-H-P · HRU-SlimAIR-500E-H-CF-P · HRU-SlimAIR-800-H-P · HRU-SlimAIR-800-H-CF-P · HRU-SlimAIR-800E-H-P · HRU-SlimAIR-800E-H-CF-P · HRU-SlimAIR-1000-P · HRU-SlimAIR-1000E-P · HRU-SlimAIR-1000E-CF-P · HRU-SlimAIR-1000-CF-P · HRU-PremAIR-350-P · HRU-PremAIR-350-CF-P · HRU-PremAIR-350E-CF-P · HRU-PremAIR-350E-P · HRU-PremAIR-450-P · HRU-PremAIR-450-CF-P · HRU-PremAIR-450E-P · HRU-PremAIR-450E-CF-P · HRU-PremAIR-500-P · HRU-PremAIR-500-CF-P · HRU-MinistAIR-L-250E-H-CF-P · HRU-MinistAIR-L-250E-H-P · HRU-MinistAIR-L-250-H-CF-P · HRU-MinistAIR-L-250-H-P · HRU-MinistAIR-L-325E-H-CF-P · HRU-MinistAIR-L-325E-H-P · HRU-MinistAIR-L-325-H-CF-P · HRU-MinistAIR-L-325-H-P · HRU-MinistAIR-L-350E-H-CF-P · HRU-MinistAIR-L-350E-H-P · HRU-MinistAIR-L-350-H-CF-P · HRU-MinistAIR-L-350-H-P · HRU-MinistAIR-LS-250E-H-CF-P · HRU-MinistAIR-LS-250E-H-P · HRU-MinistAIR-LS-250-H-CF-P · HRU-MinistAIR-LS-250-H-P · HRU-MinistAIR-LS-325E-H-CF-P · HRU-MinistAIR-LS-325E-H-P · HRU-MinistAIR-LS-325-H-CF-P · HRU-MinistAIR-LS-325-H-P · HRU-MinistAIR-LS-350E-H-CF-P · HRU-MinistAIR-LS-350E-H-P · HRU-MinistAIR-LS-350-H-CF-P · HRU-MinistAIR-LS-350-H-P · HRU-MinistAIR-R-250E-H-CF-P · HRU-MinistAIR-R-250E-H-P · HRU-MinistAIR-R-250-H-CF-P · HRU-MinistAIR-R-250-H-P · HRU-MinistAIR-R-325E-H-CF-P · HRU-MinistAIR-R-325E-H-P · HRU-MinistAIR-R-325-H-CF-P · HRU-MinistAIR-R-325-H-P · HRU-MinistAIR-R-350E-H-CF-P · HRU-MinistAIR-R-350E-H-P · HRU-MinistAIR-R-350-H-CF-P · HRU-MinistAIR-R-350-H-P · HRU-MinistAIR-RS-250E-H-CF-P · HRU-MinistAIR-RS-250E-H-P · HRU-MinistAIR-RS-250-H-CF-P · HRU-MinistAIR-RS-250-H-P · HRU-MinistAIR-RS-325E-H-CF-P · HRU-MinistAIR-RS-325E-H-P · HRU-MinistAIR-RS-325-H-CF-P · HRU-MinistAIR-RS-325-H-P · HRU-MinistAIR-RS-350E-H-CF-P · HRU-MinistAIR-RS-350E-H-P · HRU-MinistAIR-RS-350-H-CF-P · HRU-MinistAIR-RS-350-H-P · HRU-FlatAIR-80E-H-P · HRU-FlatAIR-80E-H-CF-P · HRU-FlatAIR-80-H-P · HRU-FlatAIR-80-H-CF-P · HRU-FlatAIR-100E-H-P · HRU-FlatAIR-100E-H-CF-P · HRU-FlatAIR-100-H-P · HRU-FlatAIR-100-H-CF-P · HRU-FlatAIR-120E-H-P · HRU-FlatAIR-120E-H-CF-P · HRU-FlatAIR-120-H-P · HRU-FlatAIR-120-H-CF-P · HRU-FlatAIR-125E-H-P · HRU-FlatAIR-125E-H-CF-P · HRU-FlatAIR-125-H-P · HRU-FlatAIR-125-H-CF-P · HRU-FlatAIR-150E-H-P · HRU-FlatAIR-150E-H-CF-P · HRU-FlatAIR-150-H-P · HRU-FlatAIR-150-H-CF-P · HRU-FlatAIR-200E-H-P · HRU-FlatAIR-200E-H-CF-P · HRU-FlatAIR-200-H-P · HRU-FlatAIR-200-H-CF-P · HRU-FlatAIR-225E-H-P · HRU-FlatAIR-225E-H-CF-P · HRU-FlatAIR-225-H-P · HRU-FlatAIR-225-H-CF-P · HRU-FlatAIR-250E-H-P · HRU-FlatAIR-250E-H-CF-P · HRU-FlatAIR-250-H-P · HRU-FlatAIR-250-H-CF-P
- Last updated
Registers (49)
49 read, 23 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Error Status (R) | Read | ||||
| Work Mode (RW) | Read and write | ||||
| Exhaust temperature sensor (R) | °C | Read | |||
| Extract temperature sensor (R) | °C | Read | |||
| Inlet temperature sensor (R) | °C | Read | |||
| Supply temperature sensor (R) | °C | Read | |||
| Pre-heater thermostat (R) | Read | ||||
| Afterheater thermostat (R) | Read | ||||
| Bypass status (R) | Read | ||||
| SAP signal (R) | Read | ||||
| Pre-heater status (R) | Read | ||||
| Afterhater status (R) | Read | ||||
| Bypass position (R) | % | Read | |||
| Time Mode OUT (RW) | Read and write | ||||
| Time Mode PARTY (RW) | Read and write | ||||
| Fireplace Mode (RW) | Read and write | ||||
| Supply fan speed (R) | % | Read | |||
| Exhaust fan speed (R) | % | Read | |||
| Supply fan speed - Speed 1 (RW) | % | Read and write | |||
| Supply fan speed - Speed 2 (RW) | % | Read and write | |||
| Supply fan speed - Speed 3 (RW) | % | Read and write | |||
| Exhaust fan speed - Speed 2 (RW) | % | Read and write | |||
| Exhaust fan speed - Speed 3 (RW) | % | Read and write | |||
| Exhaust fan speed - Speed 1 (RW) | % | Read and write | |||
| Flow setpoint supply (R) | m³/h | Read | |||
| Supply fan flow - Speed 2 (RW) | m³/h | Read and write | |||
| Flow setpoint exhaust (R) | m³/h | Read | |||
| Flow reading supply (R) | m³/h | Read | |||
| Flow reading exhaust (R) | m³/h | Read | |||
| Supply fan flow - Speed 1 (RW) | m³/h | Read and write | |||
| Supply fan flow - Speed 3 (RW) | m³/h | Read and write | |||
| Exhaust fan flow - Speed 1 (RW) | m³/h | Read and write | |||
| Exhaust fan flow - Speed 2 (RW) | m³/h | Read and write | |||
| Exhaust fan flow - Speed 3 (RW) | m³/h | Read and write | |||
| GHE status (R) | Read | ||||
| GHE mode (RW) | Read and write | ||||
| GHE winter temperature (RW) | °C | Read and write | |||
| GHE summer temperature (RW) | °C | Read and write | |||
| Filter alarm (R) | Read | ||||
| Turn ON/OFF (RW) | Read and write | ||||
| Supply filter days left (R) | days | Read | |||
| Exhaust filter days left (R) | days | Read | |||
| Supply air filter - depletion (R) | % | Read | |||
| Exhaust air filter - depletion (R) | % | Read | |||
| Reset filter counting (RW) | Read and write | ||||
| Bypass control (RW) | Read and write | ||||
| Airing time mode (RW) | Read and write | ||||
| Humidity indoor (R) | % | Read | |||
| CO2 indoor (R) | ppm | Read |
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Use cases
- Monitor supply and exhaust temperatures on a live dashboard to verify heat recovery efficiency.
- Create an alert when filter depletion reaches a critical level or remaining days drop below a threshold.
- Remotely switch the ventilation work mode or turn the unit on and off without an on-site visit.
- Track indoor CO2 and humidity trends over time to ensure healthy indoor air quality for occupants.
- Adjust fan speed and airflow setpoints for Speed 1 through Speed 3 from the cloud during commissioning.
- Log bypass position and GHE status to verify seasonal free-cooling operation.
Installation
Connect the ModbusCloud Gateway to the HRU-P unit's PCB using the RS-485 A, B, and GND terminals, following the correct wiring structure for your model family (SlimAIR/PremAIR/MinistAIR or FlatAIR).
Set the Modbus RTU baud rate on the gateway to 115200 to match the Alnor HRU-P default communication speed.
Configure the Modbus slave address on the HRU-P unit and ensure it matches the address set in the ModbusCloud template.
Import the Alnor HRU-P template from the ModbusCloud template library and assign it to the correct gateway and slave address.
Verify communication by checking that live temperature, fan speed, and airflow readings appear on the ModbusCloud dashboard.
Test write functionality by toggling the work mode or adjusting a fan speed setpoint and confirming the unit responds.
Things to watch for
Communication fails after wiring. What should I check first?
Verify the baud rate is set to 115200 on both the gateway and the HRU-P unit. Also confirm that the RS-485 A and B lines are not swapped and that a common GND connection is present.
Which wiring diagram should I use for my model?
HRU-SlimAIR-P, HRU-PremAIR-P, and HRU-MinistAIR-P models share one PCB connection structure. HRU-FlatAIR-P models use a different layout. Check the Alnor installation documentation for the correct pinout before connecting.
Can I connect multiple HRU-P units on the same RS-485 bus?
Yes, as long as each unit has a unique Modbus slave address. Make sure the total cable length and number of devices stay within RS-485 bus limits, and add a termination resistor at the end of the bus if needed.
Some sensor readings show zero or are missing. Why?
Not all HRU-P models include internal humidity or CO2 sensors. If a sensor is not physically present in the unit, the corresponding register will return zero or a default value. Confirm the sensor configuration of your specific model.
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