A typical container refrigeration apparatus disclosed, for example, in Patent Document 1 cools air in a container used for marine transportation, for example.
Plants (e.g., bananas and avocados) in such a container still breathe even after harvest by absorbing oxygen in the air and releasing carbon dioxide. These breathing plants consume nutrients and water stored in the plants themselves, and the plants significantly deteriorate as their respiration rate increases. Thus, oxygen concentration in the container is preferably low to the degree that the plants do not develop a breathing problem.
Patent Document 1 discloses an internal environment control system to reduce oxygen concentration of air inside a container by generating nitrogen-enriched air higher in nitrogen concentration than atmosphere and supplying this nitrogen-enriched air into the container. When the internal environment control system reduces the oxygen concentration of the inside air, a respiration rate of plants in the container decreases, curbing deterioration of the plants.