Heat pump with frost-free outdoor coil

摘要

A heat pump having an auxiliary outdoor coil equipped with heating means preventing the surface temperature during the heating cycle from falling below 32 DEG C. The heating means comprises an electrical resistance heater in thermal contact with the fins of the outdoor coil such that heat is transferred to the fins by conduction. The system incorporates means to permit functioning immediately upon return to the heating cycle from a cooling cycle even though the pressure in the receiver of the system initially exceeds that in the indoor coil. Additionally, the system incorporates means for protecting the compressor from liquid floodback when changeover occurs from heating to cooling.