Systems and methods for defrosting an outdoor heat exchanger of a heat pump

A heat pump for conditioning an interior space, the heat pump comprising:

• an outdoor unit comprising:
• an outdoor heat exchanger that is configured to exchange heat between a refrigerant and an outdoor environment;
• an outdoor expansion device that is configured to expand the refrigerant flowing into the outdoor heat exchanger when the heat pump is operating in a heating mode;
• an indoor unit comprising:
• an indoor heat exchanger that is configured to exchange heat between the refrigerant and the interior space;
• and
• an indoor expansion device that is configured to expand the refrigerant flowing into the indoor heat exchanger when the heat pump is operating in a defrost mode;
• a thermal storage device in fluid communication between the outdoor expansion device and the indoor expansion device;
• and
• a reversing valve that is actuatable between:
• a first position during the heating mode to direct refrigerant through the indoor heat exchanger, the thermal storage device, the outdoor expansion device, and then the outdoor heat exchanger to heat the interior space and to transfer heat from the refrigerant to the thermal storage device;
• and
• a second position during the defrost mode to direct refrigerant through the outdoor heat exchanger and then the thermal storage device to transfer thermal energy to the outdoor heat exchanger from the thermal storage device.