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How Does A Refrigerated Container Works & How Its Temperature Can Be Recorded?

Reefer containers need special care after they are loaded on board ship. These containers need to be supplied with the power to keep their generator running. Once plugged in, they should be monitored closely for proper function, and repaired as required in case of malfunction. The cooling of a reefer unit is performed by air. The generator, installed on one side of the Container, streams air into the box.

In most circumstances, the air is filled in through the bottom or side of the Container. The floor of a reefer container is ordinarily a T-style floor, which indicates the air can circulate through the floor and cool the cargo from the bottom up. After stuffing, the generator can be set to the right temperature, and the Container will take care of itself from thereon. The inner temperature can be maintained, even if the outside temperature suddenly increases or decreases. While a reefer freight container is excellent at keeping the temperature of its content, it is essential to learn that a reefer cannot be used to reach the aspired temperature. Therefore, reefer products need pre-cooling up to the desired temperature before stuffing into the Container.

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In addition to cooling by air, some refrigerated containers are provided with a cooling system that uses water to cool the cargo. Many Containerships got the advantage of loading reefers under the deck. If a box is stored below the deck or sometimes even when multiple containers are stacked together in a tight space, the cooling-water system can be utilized to ventilate the generated heat outside of the box and also the area it's being stored. However, because of the high cost of a cooling water system, these types of reefer containers are declining in popularity.

A refrigerated container can also be furnished with a Genset, which is short for the generator set. This Genset can be introduced as a clip-on Genset, which involves the Genset is mounted on the Container's side and can be more easily separated after delivery or storage. The Genset can also be installed as an underslung generator set; this is when the Genset is hung (or mounted) under the Container. It is mostly employed for trailer transportation, where the Genset is mounted on the trailer. This way, only the Container has to be interchanged and not the whole trailer.

The air temperature, drawn from the refrigerated hold/container, is called "Return air temperature." It is essential to maintain the return air temperature during refrigeration.

Insulated reefer container
Insulated container requiring external refrigeration source.
Bottom air delivery.

Maintaining proper records is as important as the actual performance of the job itself. In case of any cargo damage and claims, it is most important to prove that the Due Diligence was exercised by the master/vessel from when the container was loaded on board until the time it was discharged.
Therefore, the master should keep all records to prove due diligence on board, and send them to the company immediately if requested:

Item Records

i) Supply of electric power within a reasonable time after loading reefer containers Loading checklists including the loading/plug-in times and temperatures should be maintained.

ii) Monitoring the digital & chart temperatures of all reefer containers at least twice a day. Daily reefer container temperature checklists should be maintained, and printouts from monitoring unit should be preserved

iii) Notifying booking line and/or agent immediately in case of malfunction File of Reefer Unit Trouble Report should be maintained

iv) Keeping enough spare parts in good order & Record of regular inventories, and communication to booking lines for consumption and/or supply receipts

There may be some occasions when above Item (ii) and (iii) are not possible to comply due to weather conditions. The weather reports/faxes and other records should be well maintained on board, to prove the weather conditions at such dates/times.

Coolants used for refrigeration units

Originally, all refrigerated containers were operated using the coolants R11 and R12. After the destruction of the ozone layer became an issue, and consequently, these coolants were banned by the Montreal Protocol. Several manufacturers switched briefly to R22 as a substitute coolant. However, as this is also being phased out, the two coolants R134a and R404a subsequently being introduced. Later on, R134a also banned.

Electronic controllers

Refrigeration units are nowadays controlled and regulated by electronic controllers. Depending on the features of the device, these controllers perform a variety of complex tasks. It must be noted that the controllers themselves are very often a cause of problems. Much refrigeration damage is caused by faulty controllers or the peripherals associated with them (e.g., sensors). Therefore, the controllers must be designed to be as robust as possible and to withstand the prevailing ambient conditions in terms of heat, cold and moisture

Reefer Container Shipment

Procedures and guidelines for stowage of reefer containers shall be adhered to. A reefer container list or manifest must accompany every reefer container proposed for shipment. Additionally read our article on:
  1. Reefer cargo Handling In Port
    Reefer containers shall be plugged in and supplied with ships power as soon as practicable after loading. In case it is to be done by shore hands, ships crew shall still closely monitor the operation and confirm that all reefer containers are supplied with power earliest after loading....

  2. Reefer cargo care at sea
    At sea, all reefer containers shall be monitored by checking physically at least twice daily (weather permitting). All monitored data for each reefer container on board shall be entered in a reefer monitoring log and retained for three years. Some reefer containers with special cargo (e.g., VIP cargo) come with instructions for more frequent monitoring and reporting. Such instructions shall be strictly followed. ....

  3. Commodities Shipped In Reefer Containers
    Some cargoes may require controlled humidity (e.g. flower bulbs). In such cases, many refrigeration units are only capable of reducing humidity within the cargo space, and the settings should be applied accordingly. ....

  4. Reefer Cargo Temperature Recording
    A Partlow recorder registers temperature on a pressure-sensitive circular chart over 31 day period. If the voyage transit is expected to exceed 31 days, care must be taken to ensure charts are replaced before expiry. The first chart should be placed underneath the new chart to build up a complete temperature record for the entire voyage up until arrival at the final destination. .....

  5. Reefer Cargo Maintaining Records
    Monitoring the digital & chart temperatures of all reefer containers at least twice a day. Daily reefer container temperature checklists should be maintained, and printouts from monitoring unit should be preserved.....

  6. Reefer Cargo Care During Sea Transit
    Reefer containers usually have their own refrigeration unit, with an air or water-cooled heat exchanger. They have a data logger to record the temperature. The logger may be in the form of a Partlow chart or a digital logger. They usually contain high-value cargo, and any damage to cargo would likely result in substantial claims......

  7. Reefer Cargo Defrosting
    During the operation of a refrigeration unit, a layer of ice will form on the evaporator coils depending on the temperature set, the temperature of the cargo, the amount of fresh air ventilation and the cargo humidity. The unit periodically enters a phase where heat is produced by a series of electrical bars, allowing defrosting to occur. At such times, all fans are turned off automatically to prevent heat from entering the cargo compartment. ....

  8. Basic check item prior stowing Reefer Cargo
    Stowage location of reefers must be checked against vessels reefer receptacle locations. In case reefer containers must be loaded in random locations, it must be confirmed that monitoring and repair will be possible during the voyage, and that vessel has sufficient extension cables for providing power. ....

Container handling additional guideline:

Containership cargo stowage and planning

Stacking Weights Restrictions

Lashing strength calculation

Dangerous goods stowage and segregation

Reefer Container Stowage

Out of Gauge Container Stowage

Special Container Stowage

20 or 40 or 45 feet Compulsory Stowage Locations

Irregular Stowage of Containers

Over-stow of Containers

Hatch Cover Clearance (High cube containers Under Deck )

Other matters regarding cargo stowage as necessary

How to load maximum number 20 feet container on deck ?

What are the extra precaution should be taken prior loading a 45 feet container on deck ?

Container damage in ''2 in 1'' cargo Operation

Modern containership & loading of various container types

How to load containers coming in different forms/sizes

Our additional pages contain somewhat larger lists of resources where you can find useful informations

Other info pages !

Ships Charterparties Related terms & guideline
Stevedores injury How to prevent injury onboard
Environmental issues How to prevent marine pollution
Cargo & Ballast Handling Safety Guideline
Reefer cargo handling Troubleshoot and countermeasures
DG cargo handling Procedures & Guidelines
Safety in engine room Standard procedures
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