To learn about cold chain shipping containers, let’s start with definitions taken from the World Health Organization (WHO) publication “Model requirements for the storage and transport of time and temperature sensitive pharmaceutical products“.
- Active systems: Actively powered systems using electricity or other fuel source to maintain a temperature-controlled environment inside an insulated enclosure under thermostatic regulation (e.g. cold rooms, refrigerators, temperature-controlled trucks, refrigerated ocean and air containers).
- Passive systems: Systems which maintain a temperature-controlled environment inside an insulated enclosure, with or without thermostatic regulation, using a finite amount of pre-conditioned coolant in the form of chilled or frozen gel packs, phase change materials, dry ice or others.
Both of these definitions refer to “thermostatic regulation” which is active temperature control. The thermostat provides the intelligence in the container to make the decision to activate cooling when the temperature inside the insulated enclosure rises and deactivate cooling when the internal temperature drops.
In the cold chain shipping industry, the normal tendency has been to think that a system must be an active system to have active temperature control, but such is not the case. I applaud the WHO for including the phrase “with or without thermostatic control” in its definition of a passive system. A thermostat can be designed into a passive system and the resulting system does not require any external power or fuel source, but can regulate the temperature just like an active system that requires power to operate.
With the ability to actively control the internal temperature, the passive cold chain shipping container with this new technology makes the decisions when to cool and when to stop cooling. This eliminates the need for various packing protocols used to create passive packages that do not have active temperature control.
Without the need for different packing protocols such as “ship hot, arrive cold” or “ship cold, arrive hot”, a company can ship from the northern hemisphere in the dead of winter to the southern hemisphere where it is the middle of the summer without having to take any special precautions. The active control in the passive container compensates for the wide swings in ambient temperature.
How does it work?
The passive cold chain shipping container with active thermal control uses a thermostat that senses the internal temperature in the container. When the internal temperature rises above approximately 5°C, the thermostat connects a conduction path to allow the heat in the container to flow to the “heat sink” of frozen phase change material (PCM). When the internal temperature drops below approximately 5°C, the thermostat disconnects the conduction path to stop the cooling.
In order to prevent the flow of heat from the payload area of the container to the frozen PCM except when the thermostat permits it, the PCM must be separated from the payload area. This is accomplished by vacuum panel insulation that separates the PCM from the payload area. The thermostat and the conduction path are installed through a penetration in this insulation so heat can flow through the conduction path to the PCM when the thermostat turns on the cooling.
As you can appreciate, a passive cold chain shipping container with active control has a distinct advantage over a completely passive container. The active thermal control compensates for unpredicted ambient temperature events during transit, and it eliminates the need for the various packing protocols required by passive packages that do not have active temperature control. In cold weather, active thermal control stops cooling where a passive package without temperature control continues to cool which potentially freezes the payload.
Most active systems are pallet sized shipping containers which are great for large, bulk shipments. However, there is more volume of small package shipments and this is where the passive system with active thermal control will primarily be used. It is much smaller and lighter than the smallest active system.
In conclusion, a passive cold chain shipping container with active temperature control will revolutionize the cold chain small package shipping industry.
John V. W. Howe, CTO, Sofrigam USA