Video (speaking in Finnish)
Notable changes to the original SW and HW:
Two additional Dallas sensors in heat exchanger pipes (used for research and as spare parts)
Current clamp sensor monitoring input power of the heat pump
Variable temperature delta threshold to start defrosting:
if (input) power < 500W, threshold = 4
if 900W ⇐ power < 1000W, threshold = 5
if power >= 1000W, threshold = 6