Heat transport system

A heat transport system comprising:

• a refrigerant circuit that seals therein a fluid comprising HFC-32 and/or HFO refrigerant as a refrigerant and that comprises:
• a refrigerant booster that boosts the refrigerant;
• an outdoor air heat exchanger that exchanges heat between the refrigerant and outdoor air;
• a medium heat exchanger that exchanges heat between the refrigerant and a heat transfer medium;
• and
• a refrigerant flow path switch that switches between a refrigerant radiation state and a refrigerant evaporation state, wherein
• in the refrigerant radiation state, the outdoor air heat exchanger functions as a radiator of the refrigerant and the medium heat exchanger functions as an evaporator of the refrigerant, and
• in the refrigerant evaporation state, the outdoor air heat exchanger functions as an evaporator of the refrigerant and the medium heat exchanger functions as a radiator of the refrigerant;
• and
• a medium circuit that seals carbon dioxide therein as the heat transfer medium, wherein the medium circuit comprises:
• a medium booster that boosts the heat transfer medium;
• the medium heat exchanger;
• a first medium flow path switch that switches between a first medium radiation state and a first medium evaporation state, wherein
• the medium heat exchanger functions as a radiator of the heat transfer medium in the first medium radiation state and as an evaporator of the heat transfer medium in the first medium evaporation state;
• and
• indoor air heat exchangers that exchange heat between the heat transfer medium and indoor air.