Chilled and frozen storage

 

In general, temperature is more strictly controlled in chilled-storage rooms than frozen-storage rooms.  This is in accordance to the fact that the temperature inside chilled rooms is closer to the point of initial freezing in food, which is generally close to 0°C.  Air temperature should be kept as close to 0°C. To obtain efficient heat transfer between cooling air and the products, free air flow must be secured throughout the room, see figure below. Air circulation ratio of 40 is commonly used which implies that the volume of circulating air in the room in 1 hour equals 40 times the volume of the empty room. 

airflow

Air flow in chilled room equipped with fan cooling equipment. To the left is restrained air flow due to overloading.
To the right is good air flow in the same cooling room.
(FAO Fisheries Technical Paper -340 Freezing and refrigerated storage in fisheries, 1994, 143 pp)

During chilled and frozen storage it is necessary to avoid temperature increase and temperature fluctuations. To ensure sufficient cooling the following is recommended:

  • Monitor temperature at several different locations inside the room, specially close to entrances and far away from cooling units (blowers or spirals), where higher temperature and more severe temperature fluctuations are expected
  • Equip the storage with entrances/docking stations, which minimize air exchange, e.g. with automatic power doors/sliding doors, protective strips and adjustable height gangplanks
  • Equip the storage with cooling units of sufficient cooling capacity to overcome daily temperature fluctuations
  • Limit the use of electric light, e.g. by turning off lights outside working hours
  • Avoid storing products within 1-2 m distance from the nearest entrance
  • Restrict unnecessary openings of the chilled room
  • Secure free air flow throughout the store and an air circulation ratio of 40 per hour
  • The insulation of the room should be sufficient to limit the heat flow rate per unit (inner) area to 6 to 12 W/m2

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