Here are the usage requirements for refrigeration units:

1. After loading, the original quality of the refrigerated or frozen goods should be checked and noted on the packing list.

2. During loading, strict adherence to stacking principles is required to avoid short-circuiting of cold air, which could cause uneven cooling and reduce the refrigeration efficiency of the unit.

3. For long-distance transport of frozen goods, the temperature difference between the set temperature inside the container and the actual temperature should not exceed 3℃. For transporting chilled goods, the temperature error should not exceed 0.5℃, preferably not more than 0.25℃.

4. When transporting fresh fruits and vegetables in containers, the fresh air vents should be opened promptly for ventilation. However, when transporting frozen goods, the fresh air vents should be closed.

5. When transporting chilled goods in cardboard packaging, ventilation should be carried out promptly according to the outdoor temperature and humidity to keep the air inside the container dry and prevent condensation on the outer surface of the packaging.

Cooling and Insulation

When transporting frozen goods in refrigerated containers, the operating temperature should generally not exceed -18℃. Typically, the average cooling rate of a refrigerated container is 31.3℃/h (empty container). However, after loading, due to the larger heat capacity of the cargo, the cooling rate slows down significantly, sometimes requiring 15-16 hours to reach the set temperature. If the incoming cargo temperature is high, it may take 2-3 days to reach the set temperature.

The rate of temperature rise and fall inside a refrigerated container depends on the cargo loaded inside. Once the set temperature range of -18℃±3℃ is reached, the internal temperature should be maintained stable. However, when calculating the temperature rise inside a refrigerated container without refrigeration, the following empirical formulas can be used as standard values:

1) Cooled cargo (without ventilation): 0.0054*(tw-tn)℃/h

2) Frozen cargo: 0.0067*(tw-tn)℃/h

Where tw and tn are the outside temperature and the internal temperature (℃), respectively.