A coupling sub-cooler vapor injection air source heat pump system is proposed
which consists of two sub-cooler vapor injection air source heat pumps and two triple tube heat exchangers.The defrost method involves a coupling defrost system based on traditional hot gas bypass defrost
so that the problem of liquid refrigerant evaporation is solved
which is usually encountered in the outdoor heat exchanger with traditional hot gas bypass defrost.The operation reliability of air source heat pump is improved in the environment of low temperature and high humidity.The simulation and optimization for the new system under normal heating conditions give the optimal medium temperatures and corresponding injection ratios in low temperature environment.A binary linear fitting formula for optimal medium temperatures from condensing temperature and evaporating temperature is obtained.