For the transportation of temperature-sensitive cargo goods, a special type of shipping container with already installed refrigeration units is used. Reefer containers are capable of maintaining cold temperatures suitable for cargo goods inside them. They are called refrigeration containers and are commonly known as ‘Reefer containers’ and are generally seen on ‘Reefer ships‘.
Types of Reefer Containers
Integrated reefer containers
These containers have an integrated cooling system and can be easily transported either by ship/rail/road. They depend on an external electrical power source and can be powered by a diesel power generator. They are capable of maintaining a temperature range around 60°- 40° Celsius.
Porthole reefer containers
These have ventilation holes and have a water-cooling or an air-cooling system, usually an air cooling is used. Thus, they need to be connected to a system that passes cool air into them.
Cryogenically cooled reefer containers
For a short journey (less than 20-30 days), dry ice or liquid nitrogen is used for cooling. The container remains cold as long as the cryogenic liquids are present. The only benefit is that they do not require an external power source and hence can be stored anywhere onboard a ship.
Refrigerator cargos are categorized into 2 categories
These containers contain mostly meat and fishes at a temperature around -20°C, to prevent the growth of bacteria.
These containers mostly carry dairy products, fruits and vegetables at a temperature range of 1°C to 8°C. The temperature can vary depending on the type and nature of goods being carried and the duration.
Principle and Working behind reefer containers
Reefer containers works on the principle of refrigeration. Heat always flows to the body of lower temperature from a body of higher temperature. We can extract heat from a body of lower temperature to a body of higher temperature by doing some work / providing mechanical work (by heat pump).
The liquid refrigerant at high pressure, volume and temperature are expandable through a Thermostatic Expansion Valve (TEV), this expansion results in a little fall in pressure and a large fall in temperature. The vaporized refrigerant is then allowed to be in contact with the place to be cooled, through flowing in evaporator coils, then it absorbs heat and again condenses to liquid. This process continues. Further, the insulation of the container isolates it from the outside high temperature and thus prevents the temperature from rising back to normal and the container is kept cool for a longer duration.
If cargo is meat/fish/flesh, holds should be swept and cleaned after discharge of cargo. If the container is badly littered, careful detergent washing with a high-pressure machine must be done. It should not be pointed at a 90-degree angle, but horizontal for proper removal of dirt.
The cooler room, containing evaporator coils and blowers must also be cleaned from time to time. Bilges and scrapper should be working and capable of pumping the bilge dry. Brine traps that prevents warm air from entering the compartment and cold escaping must be checked, tested and refilled. All airflow channels must be cleaned and checked for blockage. If space is cluttered up, air circulation will be throttled. Fresh air valves and ducts should be free and clear. Circulation fans should be working properly.
The refrigeration system should be cleared of leakage and be in working condition, suitable for the intended voyage. All sensors and recording equipment must be in proper working condition. The thermometer should be in position and plugs tightly welded. There should be no leakage/break in insulation. Sufficient storage materials like walking board, sling, T-bars etc. should be available. The vessel should be 360 quality certified.
Cost of a Reefer container
The cost of a Reefer container is higher as compared to normal shipping containers due to the thick insulation and refrigeration unit.
- A 20ft reefer container costs around $5700-$7000.
- A 40ft reefer container costs around $10,000-$12,000.
However, containers can also be rented within price range of $30-$85 per day, depending on size, and customization required