Cascade unit and refrigeration cycle apparatus

A refrigeration cycle apparatus comprising

• a first circuit in which a heat medium conveying heat flows and that includes a first heat exchanger that exchanges heat between a heat source and the heat medium;
• a second circuit in which a refrigerant flows and that includes a compressor and a second heat exchanger that exchanges heat with indoor air;
• a cascade heat exchanger that exchanges heat between the heat medium flowing in the first circuit and the refrigerant flowing in the second circuit;
• and
• a cascade unit comprising:
• the compressor;
• the cascade heat exchanger;
• an electric component;
• a cooling portion that cools the electric component by the refrigerant flowing through the second circuit;
• and
• a cascade casing that accommodates the compressor, the electric component, and the cooling portion,
• wherein the refrigerant is a refrigerant including a carbon dioxide refrigerant, and
• the refrigeration cycle apparatus includes a controller that controls a state of the refrigerant flowing through the cooling portion to be equal to or less than a critical pressure or equal to or less than a critical temperature.