Reefer containers

This time our blog will focus on reefer containers.

Refrigerated containers (also known as reefer containers or reefers) are containers that have usually been equipped with their own reefer machine so that the inside temperature can be adjusted to being cold or warm, anything between -35 °C and +15 °C degrees. The first reefer containers were modified from the cooling spaces of lorries and were already in use in the 1960s, but the actual reefer containers equipped with their own machines came into the picture in the 1970s.

There are also more specialized (and way more expensive) freezer containers intended mainly for laboratory use, where the temperature can be set to as much as -65 degrees Celsius or +40 degrees. Superfreezer containers are also used in shipping, especially for the transportation of more demanding fish and shellfish, so that their taste and structure will remain similar to what it was when they were captured. 

Some containers have other special features, for example, the so-called controlled atmosphere, which can be used to control the balance of oxygen, carbon dioxide and nitrogen as well as the moisture of the air. However, these are rarely seen and we will focus on the more common models in this text. 

Porthole containers with hatches at the end.
Photo: Dr. Karl-Heinz Hochhaus / Creative Commons
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Usually refer containers are rented for food storage. For example, berry pickers and hunters use them in the summer and in the autumn for storing berries and hanging meat. Christmas hams are stored in containers during the holidays, and they have also been used for example to eliminate pests from furniture, among other things.

Temperature alone is not critical for food, as the ventilation feature of the machine has a major role for preservation. Many fruits and vegetables for example release gases that can cause the other fruit to ripen prematurely. Bananas are the largest single thing that is transported in shipping containers.

As much as 20% of all reefer shipments are banana shipments!

Reefer containers can be divided roughly into two different categories: the nowadays most common versions that have a built-in machine (which still requires electricity) and the so-called Porthole containers (also called Conair containers) that require an external machine for cooling. Porthole containers are becoming less and less popular.

Maintenance of reefer containers during the unloading of a ship at Oulu harbour in 2016. The containers have built-in machines.

Reefer containers in shipping use

A diesel generator attached to a reefer container that also has its own machine (underneath).
Photo: Ursula Horn / Creative Commons
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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.

Clip-on cooling system on land.
Photo: Dr. Karl-Heinz Hochhaus /
Creative Commons
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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.

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