To calculate and monitor the performance of my heat pumps (COP), I added several DS18B20 temperature sensors and a current sensor to measure the compressor's power input.

The temperature sensors are mounted in all relevant locations on the heat pump, such as the compressor discharge, and they terminate at a common ESP32. From there, the data is sent via MQTT to my Node-RED and CodeSys PLC. //Please don't judge me for my power supply. ;)

The COP calculation is still a bit off, but it is improving, and I can monitor the performance and power consumption over time via InfluxDB.