Many people assume that the refrigeration units in refrigerated trucks can arbitrarily cool or heat the cargo loaded in the compartment to the necessary temperature. However, the refrigeration unit is actually used to maintain the temperature of the cargo, not to lower the cargo’s temperature. It’s somewhat similar to using a blanket to keep cold drinks cool in the past; it wraps the cargo, and as external temperature enters the truck body through radiation, conduction, and convection, the cold air blown by the refrigeration unit carries it away, isolating the heat from the cargo.
Cargo Needs to Be at Required Transport Temperature to Avoid Spoilage
If cargo with a temperature that is too high or too low is loaded into the refrigerated truck and the refrigeration unit is set to the necessary transport temperature, it may take some time for the cargo’s temperature to reach the required level. However, the reality is the opposite; not only will the cargo’s temperature not decrease (or increase), but it may also cause the cargo to get damaged or spoil.
The cold air blown by the refrigeration unit can cause the cargo’s temperature to change, leading to moisture loss in the cargo, which results in quality changes, reduced storage time, or even spoilage.
For instance, fresh vegetables transported in a refrigerated truck might arrive at the destination drier and lighter, causing inconvenience. This is why refrigerated trucks usually pick up cargo from cold storage rather than directly from farms.
Pre-Cooling or Pre-Heating the Compartment Before Loading
Before loading cargo, the compartment must be pre-cooled or pre-heated for about 1.5 hours. Since the vehicle is often parked outdoors, the compartment temperature is typically the ambient temperature, which usually differs from the required transport temperature of the cargo. If the cargo is loaded into a compartment at ambient temperature, it could affect the cargo’s quality. Therefore, the compartment must be pre-cooled to the necessary temperature before loading.
Turn Off the Refrigeration Unit During Loading and Unloading to Minimize Temperature Loss
It’s essential to turn off the refrigeration unit during loading and unloading. Many people think keeping the unit on will slow down the temperature rise of the cargo, but this is a misconception.
If the refrigeration unit is not turned off when the compartment door is opened, the evaporator fan of the unit, which is in operation, will blow cold air out from the top of the compartment while quickly drawing in hot air from outside at the bottom. This causes the compartment temperature to rise rapidly. If the unit is turned off during loading and unloading, air movement stops, the air pressure inside and outside the compartment equalizes, and the hot air enters more slowly.
Cargo Placement Matters – Ensure Proper Cold Air Circulation
When placing cargo, consider the circulation of cold air within the refrigerated compartment. Ideally, cargo should be stacked on double-sided pallets. Fresh cargo pallets should not be wrapped in plastic film, as it obstructs the flow of circulating cold air. There should be at least 23 cm of space between the top of the cargo and the roof of the compartment.
Regularly Clean the Refrigerated Compartment to Maintain Hygiene
Cleaning the refrigerated compartment serves two purposes. Firstly, it maintains the internal hygiene, preventing unpleasant odors. This is similar to refrigerators; if not cleaned regularly, they can develop bad smells. Refrigerated trucks often transport various goods, especially fish and meat, so it’s best to clean the compartment after each use.
Secondly, regular cleaning prevents the evaporator fan of the refrigeration unit from drawing impurities into the evaporator coils, which can reduce the cooling efficiency of the unit. This is one reason why the cooling efficiency of refrigerated trucks may decrease after several years of use.
