It is customary that rented reefer containers are transported empty for from one place to another and only put to use there, but some are also transported with cargo on board from the ship to the store. For long journeys, the content is usually loaded on the refrigerated spaces of lorries.
Globally food is also transported with reefer containers being in use during transportation. The amount of reefer containers in use during transportation in ships and trains is dependent on the amount of electricity the ship/train is capable of providing.
Some lorries have a generator that runs on diesel. The downside to this is that the smell of diesel and exhausts also becomes attached to the food supplies inside the container. These diesel machines may be used as additional power sources on ships as well if the power output of the ship itself isn’t enough for the number of containers on board. Usually, products that need to be refrigerated are primarily transported on lorries that have their own cooling spaces and machines.
In addition to reefer containers equipped with their own machine, there are also Porthole reefer containers. These are basically insulated containers, as they don’t have their own cooling system. Porthole containers are used mainly for ship freight so that the cooling system of the ship will blow cold air inside the container from the opening on the foot of the end of the container. The air rises up via the floor and returns back to the cooling system through the ceiling and the opening at the upper part of the end of the container as ”warm” air. When the container is on land, it is kept cool with the help of a ”clip-on” system that is kind of like the machine in a normal reefer container, but separate from the container.
These models aren’t largely in use anymore though; instead, the containers that are used at sea are also equipped with their own cooling machines. Using a container that doesn’t have the machine in it may however be a good idea when transporting certain dangerous materials.
Reefer containers with machines
|The machine at the end of the reefer containers is connected to power current.
As we mentioned earlier, nowadays the term reefer container/refrigerated container refers to the models that are equipped with their own machines (this is the case in this article too, unless otherwise mentioned). In other words, the container itself contains a ”generator” that functions in a similar way to the external mechanism used in porthole containers:
The cooling system’s cooling agent cools the air and pushes it to the container from underneath the floor, and the air returns back to the system through the ceiling as “warm” air in order to be cooled again. As the air circulates through the container, it is important not to pack the container too full. Usually, there needs to be about 12cm of empty space beneath the ceiling (this has often been marked with warning stickers) and the floor area shouldn’t be fully covered with objects.
Sometimes we run into reefer containers that are cooled with water, but this is becoming increasingly rare due to the expensive price, so the method presented above is the most common. Liquid nitrogen and carbon dioxide ice (”dry ice”), i.e. cryogenic freezing, are also used every now and then for keeping the products cool.
Different manufacturers offer containers with different kinds of cooling machines (e.g. Daikin, Thermo King, Carrier etc.). Naturally, the weight of the machine will take away some of the allowed load capacity. The machine manufacturers are paying more and more attention to the energy efficiency of the machines. Even though we program the temperatures of the containers according to the customer’s wishes before the container is delivered, it is relatively easy to adjust the temperature of the container yourself, and simple instructions for some of the most common models can be found from the reefer container section on our site.
The structure of the containers
The inner walls of reefer containers are made out of stainless steel; the floor is stainless steel or aluminium. Due to this and the ventilation, there really is no actual possibility of water damage. The floor of the container can either be flat or equipped with a gridiron. The advantage of a flat floor is that it is easier to transfer goods to the container with trolleys that have wheels than it would be if the floor had a gridiron. The downside is that it becomes slippery easily. The gridiron floor allows for better air circulation, as the options are quite limited for the air to rise up if the floor is flat.
|A reefer container that has been decommissioned and modified to be used as an insulated container. This container has a gridiron floor.
As a rule, reefer containers are available with the lengths of 10′ (3m), 20′ (6m) and 40′ (12m) – just like shipping containers. The high cube model, which is around 30cm higher than a normal container, is also available as a reefer container, as well as the extra-large model that is 45′ long. The outer dimensions of a reefer container follow the ISO 6346 standard, so the measurements are the same as for shipping containers generally. The walls, floor and ceiling of the container usually have about 100mm of polyurethane isolation.
|10′ High Cube reefer container
The most common problems due to misuse are the gathering of ice, especially near the door, if the weatherstrips are allowed to get into poor shape and the door won’t close tightly because of this. Another common reason for a maintenance visit is that the antifreeze agent has run out.
When a reefer container is decommissioned, it takes only little to make it an isolated container. Some reefer containers already have lights in them, but it is common to add radiators and electrical sockets in connection with the isolation.