When the door of a refrigerated body opens, the heavy cold air flows out through the bottom of the opening while warm, humid air comes in at the top. One study reports that in delivery trucks this infiltration can account for about 34 per cent of the refrigeration load, and that the share grows as openings get longer or more frequent. A door opening touches fuel, product temperature and round time at once, yet it appears in few reports.
A one-week sheet gives the number. At each opening the driver marks:
- Time, stop and what was opened (vehicle door or container lid).
- How long it stayed open.
- The reason: delivery, forgotten case, paperwork, empties.
Put the openings on the same timeline as the product-zone readings; vehicle-air readings do not stand in for product temperature. The reason column points to the fix: take each stop's load and the empties in one opening, have the paperwork ready before the door opens. If the load travels split by stop in separate containers, the driver does not hunt inside the body and the air in a closed container does not change; the thing to count becomes the container lid. Compare the change on similar routes before and after.
