Heat pump system

A heat pump system comprising:

• a heat-source-side refrigerant circuit having usage units connected to a heat source unit via refrigerant communication tubes, the heat source unit having a heat-source-side heat exchanger and a heat-source-side compressor configured to compress a heat-source-side refrigerant, and the usage units having first usage-side heat exchangers;
• and
• a controller configured to carry out a heating operation in which an aqueous medium is heated by heat radiation of the heat-source-side refrigerant in the first usage-side heat exchangers,
• the usage units further having second usage-side heat exchangers that function as an evaporator of the heat-source-side refrigerant, and
• the controller being further configured to cause the heat-source-side heat exchanger to function as an evaporator of the heat-source-side refrigerant or as a radiator of the heat-source-side refrigerant in accordance with an overall heat load of the plurality of first and second usage-side heat exchangers when the heating operation or a cooling operation has been set for each of the usage units, the aqueous medium being cooled by evaporation of the heat-source-side refrigerant in the second usage-side heat exchangers in the cooling operation, and
• to carry out an operation to balance an overall heat load of the plurality of first and second usage-side heat exchangers.