Refrigerated transport

Refrigerated transport is an important link in fresh supply chains. The topic covers maritime transport and road transport. Maritime transport is performed with reefer containers, road transport ranges from semi-trailer to minivan. Although the purpose is the same: transporting the fresh products with minimum quality loss, the transportation method requires different background knowledge.

Road transportation in a refrigerated truck. Photo by WUR

Reefer containers are stacking at yard.

Refrigerated transport vs. refrigerated storage

Refrigerated transport has a lot of analogies with refrigerated storage, but also a distinct difference: movement from A to B.

This movement has multiple consequences:

  • First: space and weight limitations to the climatization equipment, as one is paid to carry goods, and not the climatization installation, from A to B.
  • Second: versatility in application domain. After moving e.g. pears at -1.0 °C from A to B, it is effective to move a new cargo from B to C and that may e.g. be frozen fish at -22 °C.
  • Third: uncertainty about ambient conditions. When building a storage facility in location X meant to operate in only 6 months of the year the expected range of ambient conditions can be in a pretty narrow band. Transport equipment moving from A to B to C to wherever at any time of the year should be prepared for a much broader ambient conditions.

This means that the moving refrigeration system needs our special attention. For example, the diversity of cargos and ambient conditions results in a diversity of frost loads to the evaporator making defrost control in transport more challenging than in storage, and making the need for good automatic defrost control more pressing.

Reefer containers in a port. Photo by WUR
Reefer containers in a port. Photo by WUR

Reefer transport

Seagoing reefer containers are designed to maintain set temperatures between -30 and +30 °C in virtually all ambient conditions. This means that they are equipped with enough cooling and heating capacity. Because sea transport tends to take multiple weeks, it sometimes pays off to control more than only temperature. That is why in reefer containers, additional features are commonly available, such as selectable fresh air exchange, dehumidification and controlled atmosphere.

Refrigerated road transport vs. refrigerated sea transport

Although both refrigerated road transport and refrigerated sea transport of fresh products requires a moveable refrigeration unit, there are important differences in the characteristics of both forms of refrigerated transport. The table below lists the most important ones.
Characteristic Road equipment Reefer container
Dimensions From semi-trailer till minivan 40 ft, sometimes 20 ft
# Pallet positions 26 (in semi-trailer) 20
Internal width up to 2.50 m 2.29 m
# Times that door opens during transport In delivery transport up to every 30 minutes Usually none
Multi-temp available Around 20% of trucks and semi-trailers None
Typical trip duration < 1 day > 2 weeks
Power supply Diesel, semi-trailers may be self supprting Electric, dependent on external power source
Fresh air exchange facility Usually none Yes, fixed m3/h setting or CO2 based
Humidity control? No Yes (dehumidification)
Controlled atmosphere (O2, CO2) No Yes, in part of the reefers
Certification for cooling/insulation ATP None
Air delivery Top Bottom
Air ducts Optional Standard

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