A passive cold chain is an arrangement that consumes no energy during carriage: the cold is stored beforehand in frozen eutectic plates or dry ice, and an insulated container keeps that cold beside the goods. Nothing runs on the vehicle; the engine can stop, the vehicle can change, the power can fail, and the arrangement stands.
How the system works. As a frozen plate melts it draws heat from its surroundings; the insulation slows the heat coming in from outside. The balance of the two holds the target condition in the container for a defined period. The energy bill is paid not on the road but at the depot where the plates freeze, in many businesses on the night tariff.
Pre-cooling is the system's third leg. GEBHARDT recommends 12-20 hours of pre-cooling for Isotec TBX and gives the preparation targets as 0 to +2 °C for the fresh zone and -21 to -25 °C for the deep-freeze zone. Load goods into an unprepared container and the plate spends its cold on the container itself first.
Where it is strong
On delivery rounds: doors open often, the route is fragmented, and the cold needs preserving at every stop rather than regenerating. With mixed loads: fresh and frozen travel in one vehicle, in separate containers under separate regimes. On the fleet side: the vehicle stays standard, hired vehicles can be used, and there is no refrigeration unit to maintain or break down.
Where it is not. A passive container does not produce cold. It is not expected to chill goods loaded warm, the road does not compensate for a half-frozen plate, and very long uninterrupted routes call for active cooling. The system's discipline lives at the depot: the freezing rack, freezer capacity and lid habits.
A passive arrangement rests on three preparations: a rack that freezes plates through, pre-cooling that prepares the container, and a round plan that keeps the lid shut.
Together with active systems
The two routes are not rivals. Plenty of operations run a reefer on the long leg and passive containers on the last urban link; the cost side of that comparison has its own article, and the return of passive solutions its own heading.
Frequently asked question
How many hours of route can a passive arrangement carry?
There is no single number; the duration is set jointly by the plate regime, the starting temperature of the goods, the fill level, the ambient temperature and lid movements. GEBHARDT states that eutectic plates or dry ice can hold the cold chain for up to 24 hours; the figure for your own route is verified separately against those variables.
