Heat pump system and control method thereof

A control method of a heat pump system, which has an outdoor unit including an outdoor air heat exchanger, at least one first indoor unit including an indoor air heat exchanger, at least one second indoor unit including an indoor water-refrigerant heat exchanger, and a water circulation pipe unit connected to the outdoor unit, the at least one first indoor unit, and the at least one second indoor unit to circulate a refrigerant, comprising:

• alternately operating the at least one first indoor unit and the at least one second indoor unit, upon judging that a simultaneous operating condition of the at least one first indoor unit and the at least one second indoor unit is satisfied.

A control method of a heat pump system, which has at least one first indoor unit including an indoor air heat exchanger and a first expander, at least one second indoor unit including an indoor water-refrigerant heat exchanger and a second expander, an outdoor unit including an outdoor air heat exchanger, a compressor, and a third expander, a refrigerant circulation pipe unit connected to the at least one first indoor unit, the at least one second indoor unit, and the outdoor unit to circulate a refrigerant, and a refrigerant distribution unit to circulate the refrigerant selectively to the at least one first indoor unit and the at least one second indoor unit, comprising:

• executing a preliminary heating operation by driving the compressor, under the condition that the expander of one of the at least one first indoor unit and the at least one second indoor unit, a heating operation of which is executed, is closed and the expander of the other one of the at least one first indoor unit and the at least one second indoor unit is opened, before the heating operation of the one of the at least one first indoor unit and the at least one second indoor unit is executed.