Reefer containers usually have their own refrigeration unit, with an air or water cooled heat exchanger. They have their own data logger to record 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 claims.
The common goal is the prevention of claims, and to ensure that the cargo transit is carried out in a safe and efficient manner with minimum loss of product quality.
A reefer container is designed to maintain cargo at the pulp temperature prevailing at the time of stuffing. Although the container machinery over a period of time can bring cargo delivered at too high a temperature down to (or closer to) the designated temperature, this is not the primary function of a reefer container.
If a container is loaded with a cargo where the pulp temperature exceeds the carriage temperature stipulated by the shippers, the "Warm" or Hot cargo will cause the temperature of the delivery air to raise very rapidly when passing up and through the cargo. Eventually, the return air may reach a temperature level whereby the refrigeration machinery cannot cool it down sufficiently prior to re-circulating it as delivery air. In this event, the tracking pattern on the chart or logger will show a temperature higher than that of the temperature control setting.
The delivery/return air differential will in most cases narrow as the continuous circulation of air, being cooler than the cargo, brings the cargo temperature down towards the desired level. Any rise in return air temperature will be arrested as the refrigeration unit begins to run in standard operational mode.
In cases where the stuffing temperature is higher than the stipulated carriage temperature, the refrigeration unit will cool down the surface layer of the cargo relatively quickly (within days). However, the centre of the stow will not reach the desired temperature for a considerable period of time.
The temperature of a cargo stuffed into a refrigerated container should not, in general, deviate by more than 3°C (5°F) from the specified carriage temperature. Chilled cargo (excluding bananas) should not deviate by more than 0.4°C (1°F). This does not mean that even these deviations should be encouraged; the objective is to receive and deliver the cargo at the carriage temperature.
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