The performance of a spiral-tube heat storage tank added to a traditional cascade air source heat pump was experimentally investigated. The water temperature of different measuring points and the refrigerant temperature at the inlet and outlet of the heat storage tank were measured. The dry bulb temperature for indoor simulated conditions was 22 ℃ ± 0.1 ℃

the relative humidity was 50% ± 3%

and the dry bulb temperature for outdoor simulated conditions was ?12 ℃ ± 0.1 ℃. The characteristics of the heat storage tank in the thermal storage mode

thermal storage defrosting mode with intermittent heating

and thermal storage defrosting mode with continuous heating were experimentally studied. The experiment results indicated that the spiral-tube heat storage tank was effective for heat storage and heat release for low-grade heat sources at different temperatures. During a thermal storage defrosting mode with intermittent heating

and thermal storage defrosting mode with continuous heating

the amounts of heat release in the heat storage tank were 1642.7 kJ and 1892.4 kJ

respectively. These results can meet the requirements for defrosting and for part of indoor heating.