Domekt Komfovent C4 Plus Modbus Registers
Domekt Komfovent C4 is a AHU (Air Handling Unit) for use in a HVAC system. The C4 is an older standard use from approx. 2011 to 2016.
Connection
Connect the unit to a computer using the provided RS485/ModBus cable extruding from the top. There is no need to add 820 Ohm 5V pull-up/gnd pull-down or 120 Ohm termination. It works fine as is.
The pin-out is as the following:
| RJ-45 flat cable | Wire color | Function |
|---|---|---|
| Pin 1 | Color | Not used |
| Pin 2 | Color | Not used |
| Pin 3 | Red | +24VDC |
| Pin 4 | Yellow | RS485 A+ |
| Pin 5 | Green | RS485 B- |
| Pin 6 | White | Gnd |
| Pin 7 | Color | Not used |
| Pin 8 | Color | Not used |
Modbus settings
To establish a working connection, it's important to match the following connection parameters. A single wrong setting will make the connection not work at all.
| Bits per second/baudrate | 19200 |
| Data bits/word length | 8 |
| Parity | Even |
| Stop bits | 1 |
It is also important to use the correct Modbus ID. It's the identifier on the bus and has to be correct in order for communication to happen with the AHU.
The C4 unit has a different Modbus ID than later models, so make sure to double check. Either of the following will work with only one unit on the Modbus line.
| Modbus ID | 20 (specific identification address) | 254 (common identification address) |
Register list
The C4 unit uses the following Modbus data register functions to read and write data.
A CR2032 battery keeps the registers concurrent when the unit is unplugged, ex. the time and date.
| Read data: | Function code 03 | Operation status, temperatures, fans speed, and etc. |
| Write data single register: | Function code 06 | Turn on/off unit, set temperature, change auto/manual mode |
| Write data multiple registers: | Function code 16 | Set values with decimals/floating integers |
Controller registers available on the C4 unit.
General settings and status
| Modbus register | Type | Access | Range | Description | Data values |
| 1000 | Read/write | Integer | 0..1 | C4 Start/stop unit | 1-Start, 0-Stop |
| 1001 | Read/write | Integer | 0..1 | Season, heating enabled or prohibited | 1-Winter, 0-Summer |
| 1002 | Read/write | 2x Char | 0x0000..0x2359 | Time, hh:mm | Ex. 8:05 => 0x0805 |
| 1003 | Read/write | Integer | 1-7 | Day of the week | 1-Mon, 2-Tue, 3-Wed, 4-Thu, 5-Fri, 6-Sat, 7-Sun |
| 1004 | Read/write | 2x Char | 0x0101..0x1231 | Month-day date | Ex. 9th May => 0x0509 |
| 1005 | Read/write | Integer | 1900-2100 | Year date | Ex. 2023 |
| 1006 | Read/write | Integer | 1..100 | Modbus ID, default 20 | Ex. 20 |
| 1007 | Read | Integer | - | Alarm status (warnings) | 14-Service, 13-Heater off, 11-Rotor stop |
| 1008 | Read | Binary | b0-b7, 0..1 | Alarm status (stop flags) | b1-Supply sensor B1, b2-Heater overheating, b3-Water temp. low, b4-Rotor stop, b5-Frost possibility, b6-Air temp. high, b7-Air temp. low |
| 1009 | Read | Integer | 3..28 | Alarm status (stop code) | 3-Rotor stop, 4-Heater overheating, 9-Supply sensor B1, 19-Air temp. low, 20-Air temp. high, 27-Water temp. low, 28-Frost possibility |
| 1010 | Read | Integer | 0..100 | Recuperation level (heat exchanger) | 0 to 100% |
| 1011 | Read | Integer | 0..100 | Electric heater level (heating element) | 0 to 100% |
| 1012 | Read | Integer | 0..100 | Water heating level (external) | 0 to 100% |
| 1013 | Read | Integer | 0..100 | Water cooling level (external) | 0 to 100% |
Ventilation settings and status
| Modbus register | Type | Access | Range | Description | Data values |
| 1100 | Read/write | Integer | 1..3 | Ventilation level (manual mode) | 1-Low fan speed, 2-Normal fan speed (recommended), 3-High fan speed |
| 1101 | Read | Integer | 0..4 | Ventilation level (current operation) | 0-Off, 1-Low fan speed, 2-Normal fan speed, 3-High fan speed, 4-Override mode |
| 1102 | Read/write | Integer | 0..1 | Mode (Auto/Manual) | 0-Manual (set fan speed), 1-Auto (schedule) |
| 1103 | Read/write | Integer | 20..100 / 0 | Intake ventilation intensity level 1 (EC-type fan) | 20 to 100% (EC-fan only) |
| 1104 | Read/write | Integer | 20..100 / 0..2 | Intake ventilation intensity level 2 (EC-type fan / AC-type fan) | 20 to 100% (EC-fan), 0 to 2 (AC-fan) |
| 1105 | Read/write | Integer | 20..100 / 0 | Intake ventilation intensity level 3 (EC-type fan) | 20 to 100% (EC-fan only) |
| 1106 | Read/write | Integer | 20..100 / 0 | Intake ventilation intensity level 4 (EC-type fan) | 20 to 100% (EC-fan only) |
| 1107 | Read/write | Integer | 20..100 / 0 | Exhaust ventilation intensity level 1 (EC-type fan) | 20 to 100% (EC-fan only) |
| 1108 | Read/write | Integer | 20..100 / 0..2 | Exhaust ventilation intensity level 2 (EC-type fan / AC-type fan) | 20 to 100% (EC-fan), 0 to 2 (AC-fan) |
| 1109 | Read/write | Integer | 20..100 / 0 | Exhaust ventilation intensity level 3 (EC-type fan) | 20 to 100% (EC-fan only) |
| 1110 | Read/write | Integer | 20..100 / 0 | Exhaust ventilation intensity level 4 (EC-type fan) | 20 to 100% (EC-fan only) |
| 1111 | Read/write | Integer | 0..1 | Override/"OVR"-mode | 0-Disable, 1-Enable |
| 1112 | Read/write | Integer | 1..90 | Override mode timer | 1 to 90 minutes |
| 1113 | Read | Integer | 0..90 | Override mode timer (current count down) | 0 to 90 minutes |
| 1114 | Read | Binary | 0..1 | AHU / Air Handling Unit fans status | 0-Stopped, 1-Operating |
| 1115 | Read | Integer | 0..100 | Supply fan level (current level) | 0 to 100% |
| 1116 | Read | Integer | 0..100 | Exhaust fan level (current level) | 0 to 100% |
