This study explores the energy consumption during the defrosting process of a cascade air-source heat pump with phase-change energy storage for defrosting and from where it comes. Experiments are carried out at an outdoor temperature of ?9 ℃

relative humidity of 85%

and frosting volume of 1.5 kg. The experimental results show that the defrosting energy is mainly used in melting the frost layer

vaporizing the retained water

heating the fins and coils of evaporator

heat transfer with the ambient air

and heating the melted water. The proportion of each part is 15.7%

15.0%

23.4%

38.0%

and 7.9%

respectively. During the defrosting

the defrosting energy mainly comes from the heat released from the thermal accumulator to the lower pressure stage

heat stored in the system before defrosting

and heat provided by the compressor at lower pressure stage. The proportion of each source is 45.2%

30.4%

and 24.4%

respectively.