If anyone is interested in building your own heat pump efficiency monitor, this has worked out well. At least qualitatively, it is very useful to see how the COP is affected by changes to the system (setting the outdoor unit capacity high/low, fast/slow responding, changing water flow rate, flow and return temperatures).
This project is a Coefficient Of Performance heat meter for an air-to-water heat pump, using an ESP8266 board with OLED display.
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 other data to MQTT and the screen. An IOTstack RPI collects and plots the data.
Current working code here: GitHub - dalklein/esp_COP_meter
Some discussion here: Reddit - Dive into anything
