Heat exchanger unit, header part, and method for manufacturing header part

A header member that is attached to a heat exchanger in which a plurality of first heat transfer pipes through which a first fluid flows and a plurality of second heat transfer pipes through which a second fluid different from the first fluid flows are disposed to be adjacent to each other, the header member comprising:

• one first external pipe connecting portion that is disposed at a position away from an end portion of the heat exchanger and to which a first external pipe for supplying or discharging the first fluid to or from the heat exchanger is connectable;
• a first flow channel portion that is disposed between end portions of the plurality of first heat transfer pipes and the first external pipe connecting portion;
• one second external pipe connecting portion that is disposed at a position away from the end portion of the heat exchanger and to which a second external pipe for supplying or discharging the second fluid to or from the heat exchanger is connectable;
• and
• a second flow channel portion that is disposed between end portions of the plurality of second heat transfer pipes and the second external pipe connecting portion,
• wherein the first flow channel portion includes a plurality of first flow channels coupled respectively to the plurality of first heat transfer pipes,
• the plurality of first flow channels are sequentially connected in a stepwise manner and are connected to the one first external pipe connecting portion,
• the second flow channel portion includes a plurality of second flow channels coupled respectively to the plurality of second heat transfer pipes and formed independently of the plurality of first flow channels, and
• the plurality of second flow channels are sequentially connected in a stepwise manner and are connected to the one second external pipe connecting portion.