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PROJECT DESCRIPTION

ESPHome SensoStar is an open-source project designed to read heating energy usage data from Engelmann SensoStar series calorimeters and enable monitoring via ESPHome and Home Assistant.

The ESP32 periodically reads data such as accumulated energy, flow rate, supply and return water temperatures, and instantaneous heat output stored inside the calorimeter, and transmits this to Home Assistant, Web Interface, and MQTT systems via Wi-Fi or wired Ethernet based on WIZnet W5500.

Generally, calorimeter data must be viewed directly on the device screen or using a separate dedicated reader. This project extends existing meters into network-based smart energy monitoring devices by connecting the calorimeter's internal communication port to an ESP32.

WHAT IS A HEAT METER?

A calorimeter is a device that calculates the actual thermal energy consumed by utilizing the flow rate of water passing through heating pipes and the temperature difference between the supply and return water.

This project can read the following data from the SensoStar calorimeter.

• Cumulative thermal energy usage: kWh
• Cumulative heating water usage: m³
• Current thermal output: W
• Heating water flow rate: m³/h
• Supply water temperature: °C
• Return water temperature: °C
• Supply-return temperature difference: ΔT
• Calorimeter Operation and Error Status
• Calorimeter battery voltage

In ESPHome, accumulated energy and volume are registered as Total Increasing values, while temperature, flow rate, and output are registered as real-time measurements. Therefore, you can analyze changes in heating energy consumption by connecting with Home Assistant's Energy Dashboard or long-term statistics functions.

SYSTEM ARCHITECTURE

The overall data flow is as follows.

SensoStar Heat Meter
→ Internal Communication Connector
→ ESP32-S3 or ESP32-C6
→ Wi-Fi or W5500 Ethernet
→ ESPHome API / MQTT
→ Home Assistant and Web Interface

The calorimeter and ESP32 are connected using the RX, TX, and GND pins of the internal 12-pin connector.

In the project's ESPHome settings, configure the UART for calorimeter communication as follows.

Baud Rate: 2400bps

Parity: Even

Data Bits: 8bit

Update Interval: 10 seconds

The ESP32 transmits a data request frame to the calorimeter and interprets the received response data in M-Bus format. It also checks the start value, length, end value, and checksum of the received frame to prevent abnormal data from being registered as sensor values.

CUSTOM ESPHOME COMPONENT

The core of this project is the custom-made SensoStar_MBusESPHome Component.

This component analyzes the DIF and VIF information of M-Bus data transmitted from the calorimeter to determine the data type and unit.

This converts the following meter data into each ESPHome Sensor.

• Energy
• Volume
• Power
• Flow
• Flow Temperature
• Return Temperature
• Temperature Difference
• Meter Status

When an error status is received from the calorimeter, it is converted into a human-readable status message such as the following, rather than a simple number.

• Temperature Sensor Cable Break
• Temperature Sensor Short Circuit
• Flow Measurement Error
• Electronic Defect
• Reset
• Low Battery

In the normal state, OKit is displayed, and if no response is received from the calorimeter for a certain period of time, No readout from heat meterthe sensor value is treated as an invalid value along with the status.

HARDWARE VARIANTS

The project supports various ESP32 hardware configurations.

Wi-Fi Version

Connect to Home Assistant using the Wi-Fi function of the ESP32-S3 or ESP32-C6.

In the first boot state where Wi-Fi information is not configured, Sensostaryou can create an Access Point named and enter network information through the Captive Portal.

Wired Ethernet Version

The wired LAN version is configured as follows.

MCU: ESP32-C6

Ethernet Controller: WIZnet W5500

Interface: SPI

Connection Board: FFC Adapter Board

Network Interface: RJ45 Ethernet

The ESP32-C6 main board and the W5500 expansion board are connected via an FFC Adapter. The firmware sensostar_eth.yamlis configured to load a separate Connectivity Package instead of the Wi-Fi settings.

The project also includes STL files for the top and bottom 3D printed housings for wired LAN devices, so it can be manufactured as a device that can be installed around an actual calorimeter, rather than just a simple breadboard example.

ROLE OF WIZNET W5500

The W5500 serves to reliably connect calorimeter data to the network in the ESP32-C6-based LAN version.

The W5500 is connected to the ESP32-C6 via SPI and uses the following signals.

• SPI Clock
• MONEY
• MISO
• Chip Select
• Interrupt
• Reset

When the Ethernet Link is connected, the status LED turns on, and if the MQTT function is enabled, it initiates a connection with the configured MQTT Broker. The Link Status LED is implemented to turn off when the Ethernet connection is disconnected.

With the W5500, you can use a wired network even in environments where Wi-Fi signals are weak or wireless connections are unstable, such as boiler rooms or machine rooms where heat meters are installed.

In particular, since equipment measuring devices such as calorimeters are often operated continuously for a long period once installed, using a fixed Ethernet connection can reduce connection problems caused by wireless password changes or signal interference.

However, this project does not use a hybrid network method that utilizes both Wi-Fi and Ethernet simultaneously. It is structured to use either Wi-Fi or W5500 Ethernet as the network method by selecting a firmware file.

WEB INTERFACE

You can check calorimeter data in a web browser without a separate Home Assistant server through ESPHome's built-in Web Server.

You can check the following information in the Web Interface.

• Battery Level
• Calculated Power
• Energy
• Flow
• Flow Temperature
• Power
• Return Temperature
• Meter Status
• Temperature Difference
• Volume

It also provides a button to instantly re-measure the battery voltage and an OTA Firmware Update function. The Wi-Fi version also offers a feature to check the current Wi-Fi signal strength.

This feature allows users to directly check the status of the calorimeter by accessing the ESP32's IP address from a PC or smartphone connected to the same local network.

HOME ASSISTANT INTEGRATION

Using the ESPHome Native API, the device is automatically registered with Home Assistant.

Registered devices are displayed as Sensor Entities in Home Assistant as follows.

• Battery Level
• Calculated Power
• Energy
• Flow
• Flow Temperature
• Power
• Return Temperature
• Status
• Temperature Difference
• Volume

You can add each Entity to the Dashboard or use it as an automation condition. For example, you can configure it to send notifications if heating consumption increases sharply above normal, or if the heat meter runs low on battery or a sensor error occurs.

MQTT SUPPORT

In addition to the ESPHome Native API, MQTT can be used optionally.

MQTT is disabled by default, and you can configure the following information in the Web Interface or the Home Assistant Control Entity.

MQTT Broker Address

MQTT Port

MQTT Username

MQTT Password

MQTT Enable/Disable

The default MQTT port is 1883, and the entered settings are saved to the ESP32's NVS and retained even after a reboot. A verification process is also included to prevent MQTT from being enabled if the Broker Address is not entered or the Port is incorrect.

Using MQTT, you can link calorimeter data not only with Home Assistant but also with Node-RED, InfluxDB, Grafana, or your own energy management server.

LED STATUS INDICATORS

The device also features an LED function to check the current operating status.

Firmware Programming Status

Wi-Fi or Ethernet Link Status

Device Heartbeat

New SensoStar Data Received

The Heartbeat LED blinks periodically to indicate that the device firmware is operating normally.

When new data is received from the calorimeter, a separate Data LED blinks briefly, allowing you to check the communication status on-site without connecting to the network.

COMPATIBLE HEAT METERS

The storage explains that the following calorimeter has been confirmed to be working.

Engelmann SensoStar U

Engelmann SensoStar E

Water appliances Volumess VI E

Maddalena microCLIMA EVO

Maddalena microCLIMA U

Brummerhoop F90U3

Molline Wingman C3

However, since only calorimeters that support an internal communication module can be used, models without a communication module may not be compatible even if they have the same appearance.

KEY FEATURES

Real-time Heating Data Monitoring

You can check the heating energy status in a web browser or Home Assistant without checking the heat meter directly.

Wired and Wireless Connectivity

You can select the ESP32 Wi-Fi or W5500 Ethernet version depending on the installation environment.

Local Operation

You can manage data on your local network using Home Assistant, Web Interface, or MQTT Broker without relying on Cloud Services.

OTA Firmware Update

You can update ESPHome Firmware via the network without disconnecting the device.

Runtime MQTT Configuration

You can change MQTT Broker information from the Web Interface or Home Assistant without rebuilding the firmware.

Meter Error Monitoring

You can check the calorimeter's sensor open circuit, short circuit, flow measurement error, and low battery status in text form.

Open-source Hardware Expansion

The ESPHome Component, YAML settings, circuit configuration data, and LAN Housing STL file are publicly available, so you can modify them to suit your usage environment.

POSSIBLE APPLICATIONS

This project can be utilized in the following environments.

Home heating energy monitoring

Check heat usage per apartment household

Boiler and Heat Pump Efficiency Analysis

Building energy management system

Remote monitoring of district heating heat meters

Monitoring of machine room and boiler room facilities

Home Assistant-based heating automation

MQTT-based energy data collection

Long-term heating usage records and analysis

Calorimeter Error and Battery Status Notifications

CONCLUSION

ESPHome SensoStar is an open-source heating energy monitoring project that brings internal data from existing calorimeters into the ESP32 and ESPHome environment.

It is characterized by the fact that, rather than simply adding a temperature sensor, it directly reads the accumulated energy, flow rate, heat output, supply and return temperatures, and error status actually measured by the calorimeter.

In addition, it supports Home Assistant Native API, Web Interface, MQTT, and OTA Updates, enabling integration of collected data with various smart home and energy management systems.

In particular, the wired LAN version combining the ESP32-C6 and WIZnet W5500 is a project with high utility value, as it enables stable collection of heat meter data even in boiler rooms or machine rooms where Wi-Fi connections are unstable, and allows existing meters to be expanded into local network-based smart energy metering devices.