Heat Pump Defrost Cycle

Air-source heat pumps quietly fight a losing battle with the weather: whenever the outdoor coil runs colder than freezing, moisture in the air deposits onto the fins as frost, and that frost — an insulator sitting right where the machine needs heat transfer most — steadily drags the coefficient of performance down. This simulator models that fight in real time. Dial in the outdoor temperature and humidity to see how fast frost forms (fastest not at the coldest temperatures but in a narrow band just above freezing, because very cold air holds little moisture), watch the refrigerant loop reverse direction and the outdoor fan stop when the controller calls a reverse-cycle defrost, and track the cumulative energy penalty that repeated defrosting adds on top of ordinary heating.