There are many reasons that will cause the shipping container condensation. Only five key reasons will be introduced here.

1. Temperature fluctuations in containers

Temperatures that change from day to night or when moving between different climates can cause the air inside to reach the dew point, which can cause condensation. Condensation usually occurs when the contents of the container (the cargo or the air itself) are warm or humid, and the container is in a cooler environment.

2. Container humidity is too high

Container humidity is too high when there are a lot of sources of moisture in the container, such as high moisture content in the cargo itself, humid conditions during transportation, or poor air circulation in the container that prevents moisture from being removed in time. When the humid air encounters the cooler container walls or cargo surfaces, the moisture will quickly condense into droplets, just like water droplets easily appear on glass in a cool room on a humid summer day, which can not only damage the cargo, but also increase the risk of rust on metal parts inside the container.

3. Air space

The air space inside the container has an important impact on changes in humidity and temperature. Larger air space means more air can hold water vapor, and the air’s ability to hold water vapor will also change when the temperature fluctuates. For example, when the temperature is high during the day, the air can hold more water vapor, while the temperature drops at night, and the air’s ability to hold water vapor decreases. The water vapor that was originally “dissolved” in the air during the day may precipitate due to supersaturating, forming condensation, just like a cup of hot water can dissolve more sugar, and some of the sugar will precipitate after cooling. Moreover, if the air in the air space does not flow, the humidity and temperature differences in different areas will increase, making it easier to condense locally.

4. Poor ventilation

Poor ventilation is a common factor that causes problems in containers. If the ventilation system of the container is not designed properly, or the vents are blocked, etc., good air exchange cannot be achieved. In this case, the water vapor emitted by the cargo in the container and the excess water vapor generated by temperature changes cannot be discharged, and will continue to accumulate in the box, causing the humidity to continue to rise. At the same time, poor ventilation also makes the temperature distribution in the box uneven, and condensation is more likely to occur between hot and cold areas, just like in an unventilated room, corners are prone to dampness and mold.

5. Moisture content of cargo

The moisture content of the cargo itself is a key factor affecting the internal environment of the container. If the goods are not fully dried before loading, such as fresh fruits and vegetables, which contain a lot of water, they will continue to release water vapor into the surrounding air during transportation, causing the humidity in the container to rise. When this air containing high water vapor encounters the lower temperature container wall or other colder goods, the water vapor will condense into water. In addition, some highly hygroscopic goods, such as wood and textiles, will absorb a lot of water in a high humidity environment. When the ambient temperature changes, the absorbed water may be released again, further exacerbating the humidity changes and condensation in the container.