Cargo hold ventilation generally works well, but sometimes it does not, and some of these complications are difficult for people on shore to appreciate:
A. Ventilation is best if it can cool down and reduce humidity, but sometimes it will heat up when the humidity drops, or increase humidity when the temperature drops; Generally, goods are afraid of temperature and humidity. Fortunately, most goods are afraid of humidity and are not too afraid of heat, but too much heat is not enough. If both sides cannot be taken into account, they can only get wet first. Only a few goods are not afraid of heat and humidity, but can be ventilated at the same time to cool down, or even sprayed with water at the same time to cool down. Therefore, different treatment should be given to the ventilation of goods of different nature and the navigation areas and ports with different climate and meteorology, which is one of the reasons for the complexity.
B. Different temperatures in different parts of the cargo hold not only affect each other but also rise and fall by different factors. If the air temperature varies with the temperature outside the cabin and the heat emitted or absorbed by the cargo inside the cabin during ventilation; The surface temperature of the goods varies with the air temperature, temperature, characteristics of the goods and water content of the loading port. Hull plate temperature varies with seawater temperature; Deck temperature varies with temperature, sun, surf, snow and ice. In the temperature of the bulkhead and floor, the oil temperature varies with those adjacent to the fuel tank and with those separated from the engine room. Therefore, when warm and humid air into the cabin, some places in the cabin condensation dew, some places do not condensation, there are first after. That's the second reason for the complexity.
C. Theoretically cargo ventilation is equivalent to two different temperature humidity air swap places, but in fact the ventilation process is not so simple, low temperature dry outside air into the chamber to squeeze in high temperature and humidity air tank, the original is a good thing, but if enter too fast too hard, two different temperature humidity of air, near the place will be condensed water droplets, good thing into a bad thing, this is the third complexity. Generally speaking, the basic condition of ventilation is that the dew-point temperature of the air outside the cabin is lower than the surface temperature of the cargo.