How many pallets went out on a trip is easy to measure. How much of the load stayed cold is not. Turkey's vocational module on refrigerated vehicles connects the two with numbers.
The volume to leave free. According to the module, room must be left so that the cold air blown across the evaporator can reach all the goods evenly, and that volume should be at least 15 to 20 per cent of the volume of product loaded.
Fifteen per cent is close to one row of pallets. Set the gain from loading one extra pallet per trip against the risk of the whole load leaving its regime, and the arithmetic changes.
Three clearances
| Between | Minimum gap |
|---|---|
| Front wall of the body and the goods | 5 cm |
| Lower edge of the evaporator air outlet and the goods | 20 cm |
| Floor of the body and the goods | 10 cm pallet or grating |
The floor gap does two jobs: it lets air return underneath, and it separates the goods from the surface most exposed to heat from the engine and the asphalt.
The same clearance rule applies to a load going from the production line to the shelf.
Why the air returns unevenly. The module notes that air returns to the evaporator through many gaps and at widely differing temperatures. Air leaking past the doors, leaks through the walls, air passing over the goods and short-circuit air combine into a single stream. Short circuit is the key term: if the discharged air runs straight back to the return without travelling around the load, the unit runs and the product does not cool.
The module puts it directly: the refrigeration unit may have more capacity than needed, yet because the load is badly stacked and badly packed the unit cannot draw enough heat out of the product and move it outside.
The share belonging to packaging
The module asks for packaging to be sound and sealed, and for a stacking plan suited to the vehicle to be prepared in advance, taking the dimensions of the packaging or crate into account. Preparing the plan in advance is a different activity from deciding on the dock.
Inside a closed container the picture changes
When the load travels inside a closed container, the air-circulation problem moves inside that container. There, too, a gap is needed between the plate and the goods. The difference is that the volume is small and repeatable, so the same stack produces the same result every time.
