The door is open, the forklift is going in and out, and the unit is running. It is one of the most common sights on a loading bay. Turkey's Ministry of National Education module on refrigerated vehicles is unambiguous about it: after pre-cooling, the refrigeration system should be switched off and loading should begin immediately.
The three harms the module lists
- A forced-air cooling system cannot cool an uninsulated space with its door open to the outside, so fuel and energy are wasted.
- The evaporator fan throws the cooled air out of the body and the internal temperature rises.
- As much warm, humid outside air seeps in as cold air is pushed out; it condenses on the evaporator coils and then forms frost and ice.
The module closes the third point with a warning: working in these conditions can also cause serious faults in the refrigeration system. The issue is not only the cold that is lost but the unit itself.
Why the fan works against you
In a closed body the evaporator fan turns the air within a circuit. When the door opens the circuit is no longer closed. The fan does not know the door is open. It is now mixing the air between the body and the dock, and every cubic metre it blows out draws another cubic metre in from outside. The cooling looks as though it is running; what it is doing is cooling the yard.
Those three points describe where warehouse to store distribution breaks most often.
The bill for the icing arrives later
Ice building on the coil does two things: it narrows the air path and lowers heat transfer. The unit runs longer to hold the same temperature, the number of defrost cycles rises, and the internal temperature climbs during each one. Ten minutes gained on the dock is repaid over the next two trips.
The arrangement the module recommends
Loading should be planned and carried out briskly without leaving the door open longer than necessary, and an air curtain should be used inside the body where possible. An air curtain does not close the door; it slows the stream of air moving through the opening.
| Habit | What it produces |
|---|---|
| Unit on, door open, loading slow | wasted fuel, rising temperature, iced coil |
| Unit off, loading brisk, door open briefly | loss limited to the time the door is open |
| Load inside a closed container | opening the door does not reach the space holding the product |
