Heat dissipation processes
  1. Cooling with fresh air only: With this method, the ambient air on deck is drawn in and passed to each refrigeration unit with an air distribution system. If the vessel has a closed hold, it may also be necessary to install appropriate air extraction fans. A system of this type is shown in Fig. 33. The power requirements for a cooling system of this type, will depend on the design and the vessel type, and vary between 1.5 kW and 5 kW for each 40' container.
  2. Fresh air cooling with return cooling by sea water: With this method, air cooled by the sea water air cooler is circulated through the hold. This process is usually only used where it is not possible to achieve the necessary airflow cross-sections in the deck structure. The energy expenditure of this system is no more efficient than that of a cooling system using only fresh air.
  3. Sea water cooling of the containers: This method requires the use of specially designed containers which have a water-cooled condenser in addition to the usual air cooled condenser (see above). Water for cooling is then piped to the containers by the ship. However, some of the electrical power consumed must be dissipated with air from the hold since the hot parts of the refrigeration unit also give off heat to the air in the hold. A particular disadvantage of this method is that it is not suitable for use with all types of refrigerated container and thus results in very serious logistical limitations.
The general conclusion is that the removal of heat generated by refrigerated containers stored below deck requires a considerable amount of energy. Since the refrigeration units of the refrigeration containers usually have a maximum permitted ambient temperature of +45°C, this is also the maximum permitted air temperature when designing systems.

Click the graphic to enlarge.
Figure 33:
Ventilating a hold with refrigerated containers

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