Inner housing unit and fresh air system housing

The utility model relates to an inner housing unit and a fresh air system housing, and belongs to the technical field of fresh air systems. The fresh air system housing comprises an outer housing body and an inner housing body, the inner housing body is arranged in the outer housing body, and the inner housing body is formed by sequentially splicing at least three inner housing body units. The inner housing unit comprises a shell and a first access door, the shell is provided with an access hole, the first access door comprises a door frame and a second access door, the first access door can open or close the access hole, the second access door can open or close the door frame, and the opening direction of the first access door is opposite to that of the second access door. According to the fresh air system housing, no matter how the installation direction of the first access door is, a worker can open the first access door or the second access door in different directions according to needs, the requirement