Abstract: A heat pump system is provided. The heat pump system comprises a compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger and a six-way valve. The compressor comprises an air suction port and an air discharge port. The first heat exchanger is arranged in a first circulation path, the second heat exchanger is arranged in a second circulation path, and the third heat exchanger is arranged in a third circulation path, wherein the first circulation path, the second circulation path and the third circulation path are parallel paths. A first end of the first circulation path, a first end of the second circulation path and a first end of the third circulation path are connected to the six-way valve and are in controllable communication with the air suction port and the air discharge port of the compressor by means of the six-way valve.

Abstract: A heat pump unit and methods for operating the heat pump unit are provided. The heat pump unit includes a compressor (101), a throttling device (107), a first heat exchanger (104), a second heat exchanger (102), a third heat exchanger (103) and a mid-pressure tank (110). The heat pump unit operates in multiple run modes and switches between the run modes without shutdown. The first heat exchanger or the second heat exchanger is capable of acting as a condenser in the multiple run modes. When switching from a pre-switching run mode to a post-switching run mode, a control device determines whether to perform a pressure release operation to the first heat exchanger or the second heat exchanger.