A method for controlling a heat pump including an outdoor unit including a compressor and a first heat exchanger, an indoor unit including a second heat exchanger and an expansion valve to perform air stream cooling and heating operations, and a hydro unit connected among the compressor, the first heat exchanger, and the expansion valve, the outdoor unit further including a 4-way valve to change a flow direction of refrigerant in accordance with cold water and hot water operations, the method comprising: determining whether the hot water operation and the air stream heating operation are simultaneously selected, and adjusting an opening degree of a first flow rate control valve included in the outdoor unit when the hot water operation and the air stream heating operation are simultaneously selected, to adjust amounts of refrigerant respectively supplied from the indoor unit to the hydro unit and the first heat exchanger of the outdoor unit; and determining whether the hot water operation and the air stream heating operation are simultaneously selected, and adjusting an opening degree of a second flow rate control valve included in the hydro unit when the hot water operation and the air stream heating operation are simultaneously selected, to adjust amounts of refrigerant respectively supplied from the compressor to the hydro unit and the indoor unit, characterised in that the adjusting the opening degree of the second flow rate control valve comprises: identifying a capacity of the indoor unit; selecting the opening degree of the second flow rate control valve such that the selected opening degree corresponds to the identified capacity of the indoor unit; detecting an outdoor temperature; compensating the selected opening degree of the second flow rate control valve, based on the detected outdoor temperature; and adjusting the opening degree of the second flow rate control valve such that the adjusted opening degree corresponds to the compensated opening degree. determining whether the hot water operation and the air stream heating operation are simultaneously selected, and adjusting an opening degree of a first flow rate control valve included in the outdoor unit when the hot water operation and the air stream heating operation are simultaneously selected, to adjust amounts of refrigerant respectively supplied from the indoor unit to the hydro unit and the first heat exchanger of the outdoor unit; and determining whether the hot water operation and the air stream heating operation are simultaneously selected, and adjusting an opening degree of a second flow rate control valve included in the hydro unit when the hot water operation and the air stream heating operation are simultaneously selected, to adjust amounts of refrigerant respectively supplied from the compressor to the hydro unit and the indoor unit, characterised in that the adjusting the opening degree of the second flow rate control valve comprises: identifying a capacity of the indoor unit; selecting the opening degree of the second flow rate control valve such that the selected opening degree corresponds to the identified capacity of the indoor unit; detecting an outdoor temperature; compensating the selected opening degree of the second flow rate control valve, based on the detected outdoor temperature; and adjusting the opening degree of the second flow rate control valve such that the adjusted opening degree corresponds to the compensated opening degree. identifying a capacity of the indoor unit; selecting the opening degree of the second flow rate control valve such that the selected opening degree corresponds to the identified capacity of the indoor unit; detecting an outdoor temperature; compensating the selected opening degree of the second flow rate control valve, based on the detected outdoor temperature; and adjusting the opening degree of the second flow rate control valve such that the adjusted opening degree corresponds to the compensated opening degree.