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[Solved] Domoticz and the Vents VUT R 600 VE EC A21 recuperator: communication via Modbus and Raspberry Pi

Daro1003 6087 62
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How can I read a Vents VUT R 600 VE EC A21 recuperator's temperatures over Modbus TCP from a Raspberry Pi into Domoticz?

Connect to the recuperator over Modbus TCP on port 502, use the register table from the manual, and first verify that you can read the data with a Modbus master tool or Node-RED before trying Domoticz [#20561989] [#20559769] [#21421375] The thread says the BMS function is Modbus TCP and the A21 module is likely the gateway, so if that module is already in use you should work over Wi‑Fi/Ethernet rather than adding another RS485 master; start by reading InputRegister at address 0 and then other registers from the table [#20559769] [#20560537] [#20561989] For Domoticz, the working approach was to format the values in Node-RED and send them as Domoticz udevice JSON, reusing the same pattern as other devices and changing only the idx and svalue fields [#21454792] If the recuperator returns scaled integers such as 183 for 18.3°C, divide by 10 in the Node-RED flow before sending to Domoticz [#21456187] The Node-RED setup used the recuperator network settings, MQTT broker settings, and Domoticz IDX values, and a temperature-reading flow was later shared as a working example [#21460452] [#21775494]
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  • Domoticz-to-recuperator control flow pending test

    #61 21460452
    Daro1003
    Level 34  
    Posts: 2716
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    zuhjk wrote:
    Fun that you have mastered this node-red.
    .

    Rather too serious a statement but I managed to install thanks to the help of @michal.zd and thanks to a colleague from the Domoticz forum to import the flows he wrote. This colleague is so kind that he also sent a flow to control my recuperator from Domoticz level, i.e. sending commands from Domoticz to the recuperator. Unfortunately I have not had time to implement and test this yet.

    In general, I know what NodeRed looks like and I manage to do something there I think it is a good start.

    @zuhjk take a look at the topic: https://forum.domoticz.com/viewtopic.php?t=43153
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  • #62 21460679
    michal.zd
    Level 31  
    Posts: 1703
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    Daro1003 wrote:
    Generally I know what NodeRed looks like and I manage to do something in it I think it's a good start.
    .
    Once you understand and get the hang of it, it turns out to be simple.
  • #63 21775494
    Daro1003
    Level 34  
    Posts: 2716
    Help: 295
    Rate: 608
    Installing NodeRed according to these instructions:
    https://nodered.org/docs/getting-started/raspberrypi

    Flow for temperature reading in the appendix.
    You need to adjust the network data of the Recuperator and broker and the IDX in domoticz.

    Maybe it will be useful to someone although there are rather few people using domoticz anymore.
    Attachments:
    • Przepływ Rekuperator.txt (3.99 KB) You must be logged in to download this attachment.
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Topic summary

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The discussion focuses on integrating a Vents VUT R 600 VE EC A21 recuperator with Domoticz on a Raspberry Pi via Modbus/RS485. The device exposes a Modbus TCP interface through the A21 module, and the main task is to read registers such as temperatures and humidity, then pass the values into Domoticz. Initial testing is done with a PC and Modbus tools such as Radzio Master Simulator, using port 502 and reading Input Registers from address 0 or other documented offsets. It is clarified that if communication is already handled through a LAN/ETH converter, the setup should use RTU over TCP; if using USB, only RTU is needed. The thread also covers fixed IP configuration, DHCP issues, and the fact that other Modbus clients must be disabled while Domoticz is reading. Later, Node-RED is introduced as the practical solution: Modbus data is read, scaled in function nodes, and forwarded to Domoticz via MQTT or direct udevice commands. The final setup includes Node-RED installed on Raspberry Pi, imported flows for temperature reading, and a separate flow for sending control commands back to the recuperator.
AI summary based on the discussion. May contain errors.
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FAQ LABEL_AI_GENERATED

TL;DR: For 15 FAQ answers, "read 90 registers" is the practical breakthrough for Domoticz users integrating a Vents VUT R 600 VE EC A21 via Raspberry Pi, Node-RED, Modbus TCP on port 502, MQTT, and JSON temperature publishing. [#21454785] Why it matters: This lets a Raspberry Pi turn recuperator data into usable Domoticz temperature devices without relying on unstable Modbus plugins.

Path Thread setting Best use Key limitation
Modbus TCP over LAN/Wi-Fi IP + port 502 Direct A21 network access Needs fixed IP
RTU over TCP LAN converter RS485 converter path Serial defined in converter
USB RS485 RTU USB adapter Direct A+/B- testing More wiring and port setup
Node-RED + MQTT JSON to broker on port 1883 Domoticz integration Needs flow formatting

Key insight: The Vents A21 path works once the network Modbus read returns real registers. Then Node-RED only has to scale values, map Domoticz IDX numbers, and publish JSON.

Quick Facts

  • The working test path used Modbus TCP-style access to the recuperator IP on port 502 before Domoticz integration. [#20561989]
  • A successful Node-RED read used address 1 and later expanded to 90 registers, matching the Radzio program view. [#21454803]
  • Temperature values arrive scaled by 10, so 199 must be divided by 10 to display 19.9 °C. [#21454831]
  • Domoticz publishing used MQTT on broker port 1883 with JSON payloads containing command, idx, and svalue. [#21454831]
  • Remote help was considered feasible with AnyDesk, port redirects, and proper network security, especially beyond 100 km travel distance. [#21065062]

How do I connect a Vents VUT R 600 VE EC A21 recuperator to Domoticz on a Raspberry Pi using Modbus?

Connect it through the A21 network interface, then bridge Modbus data into Domoticz with Node-RED and MQTT. Use the recuperator IP, port 502, and a Raspberry Pi running Node-RED. Then publish JSON messages to Domoticz through the MQTT broker. The thread later confirms a Node-RED flow for temperature reading, requiring adjusted recuperator network data, broker data, and Domoticz IDX values. [#21775494]

What Modbus register documentation is needed to read temperatures from a Vents VUT R 600 VE EC A21 recuperator?

You need the manufacturer’s Modbus register table with register addresses and descriptions. The key requirement is knowing which input registers contain temperatures and other values. One participant states that the linked manufacturer document contains the needed base for testing. Later, another confirms the descriptions of the read data are in the document sent for the recuperator. [#21454742]

How can I test Modbus TCP communication with a Vents recuperator on port 502 using Radzio Modbus Master Simulator?

Test it from Windows by connecting Radzio Modbus Master Simulator to the recuperator IP on port 502. 1. Set Modbus TCP connection to the recuperator IP. 2. Use port 502. 3. Read Input Registers from address 0 or 1 and compare values with the Vents table. A successful read means Domoticz integration can start. [#20561989]

What is Modbus TCP and how is it different from Modbus RTU over TCP when integrating HVAC equipment?

Modbus TCP uses an IP network connection, while RTU over TCP tunnels serial Modbus RTU frames through a network converter. "Modbus TCP is a network protocol that carries Modbus communication over Ethernet or Wi-Fi, using an IP address and port 502 instead of a local serial port." In the thread, the Vents documentation suggested Modbus TCP, but screenshots looked like RTU over TCP. [#20582734]

What is RS485 and why do A+, B-, and GND connections matter when connecting a recuperator or keypad?

RS485 is the two-wire bus used by the recuperator keypad, and A+, B-, plus GND must match the device terminals. "RS485 is a serial communication standard that lets one master poll multiple slave devices over differential A/B wiring, where polarity and shared ground affect reliable frames." The original setup connected in parallel to A+, B-, and GND at the keypad. [#20558215]

How do I find or set a fixed IP address for a Vents A21 recuperator connected over Wi-Fi or Ethernet?

Find the recuperator in the router client list, then reserve a fixed IP by MAC address or set Static instead of DHCP. The thread notes that the IP must be saved somewhere in the router. It also mentions a router MAC filter option for assigning a fixed IP. Wired Ethernet allowed fixed IP setup more clearly than Wi-Fi in this case. [#20562002]

Modbus TCP vs RS485 USB converter: which connection method is better for reading a Vents recuperator in Domoticz?

Use Modbus TCP over LAN when the A21 module exposes the recuperator on the network. It avoids an extra USB RS485 adapter and uses the existing IP path. If using USB, configure RTU only and omit TCP settings. If using a LAN converter, configure RTU over TCP and avoid defining the serial port in Domoticz. [#20582549]

How do I configure Node-RED to read Modbus registers from a Vents VUT R 600 VE EC A21 recuperator?

Configure a Modbus read node for the recuperator address, then read the documented register range. The working setup used address 1 and could read 90 registers. Change the start address to reach other groups, such as 21, 31, or 41. The register descriptions must come from the Vents Modbus document used during testing. [#21454780]

How can Node-RED send temperature readings from a Vents recuperator to Domoticz using MQTT and JSON?

Node-RED sends Domoticz updates by publishing JSON payloads through MQTT. The function node creates messages with command: "udevice", a Domoticz idx, and an svalue. The MQTT broker example used IP 192.168.10.51 and port 1883. For more readings, add more idx variables and return more message objects. [#21454831]

Why do Vents recuperator temperature registers show values like 199 instead of 19.9 in Node-RED or Domoticz?

The recuperator sends temperature as a scaled integer, so divide the value by 10 before publishing it. A value of 199 becomes 19.9 °C. The shown Node-RED function uses (msg.payload[1] / 10).toString() for this conversion. This keeps Domoticz from displaying raw register values instead of real temperatures. [#21456142]

How do I map Modbus register values to Domoticz IDX devices for recuperator temperature sensors?

Map each register value to one Domoticz IDX inside the Node-RED function node. Use one idx variable per Domoticz device, then set svalue from the selected msg.payload array element. For example, idx1, idx2, and idx3 can represent three temperature sensors. Replace placeholder values like 123, 456, and 789 with real Domoticz IDX numbers. [#21454831]

What are Domoticz IDX values and how are they used when publishing MQTT data from Node-RED?

Domoticz IDX values identify the target virtual devices receiving MQTT updates. "Domoticz IDX is a device identifier that tells Domoticz which sensor or switch should receive a JSON update, separate from Node-RED’s internal node IDs." The thread warns not to confuse Node-RED id and z fields with Domoticz IDX values. [#21456951]

How can I read multiple Modbus registers at once, such as 90 registers starting from address 1, in Node-RED?

Set the Modbus read node to start at address 1 and request 90 registers. This matched the earlier Radzio program readout in the thread. When the node still displayed 10, the user adjusted the setup and confirmed the 90-register read worked. Use the resulting payload array to select specific temperature positions. [#21454803]

What should I check when Domoticz freezes or crashes after adding Modbus plugins?

Check whether the plugin matches the real transport: Modbus TCP, RTU over TCP, or USB RTU. Wrong plugin settings can make Domoticz freeze for several minutes, as reported after adding and changing plugin options. Also close other Modbus programs while Domoticz communicates, because simultaneous polling can break the session. [#20582515]

How can the same Modbus and Node-RED approach be used with other devices like a Sofar inverter or Vaillant EcoTEC boiler?

Use the same method if the device exposes Modbus and you have its register documentation. The thread mentions Sofar inverter RS485, Vaillant EcoTEC, and other Modbus devices as candidates. The interface is standard, but the register meanings depend on the manufacturer. Node-RED can then format each value for Domoticz via MQTT JSON. [#21454900]
AI summary based on the discussion. May contain errors.
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