This project is a Coefficient Of Performance heat meter for an air-to-water heat pump, using an ESP8266 node-mcu board with OLED display, only about $7.

It measures water flow from a hall-effect turbine meter, temperatures across the refrigerant to water heat exchanger with DS18b20 sensors, collects electric power consumption over MQTT from an Emporia Vue-2 monitor which has been ESPhome'd. It calculates and publishes the COP and data to MQTT and the cute little OLED screen. An IOTstack RPI collects and plots the data.