304 PRESERVATION METHODS 



density of the product involved. Precooked or breaded packaged seafoods 

 such as fish sticks, shrimp, or fish portions have space requirements of 

 about 25 to 30 pounds per cubic foot. Packaged fish fillets or fish blocks 

 have higher densities of 55 to 60 pounds per cubic foot. Round or dressed 

 fish stored in wooden boxes or stacked individually within the freezer 

 have densities ranging from 30 to 35 pounds per cubic foot. In storing 

 round fish, average weight 10 pounds, on shelves, about 1 square foot of 

 shelf space should be allotted for each 73-2 pounds of fish. In the case of 

 10-pound, 23/^-inch-thick packages of fish fillets, about 1 square foot of 

 shelf space should be allocated for each 10 to 11 pounds of fish. 



Temperature. The cold store is maintained at the desired temperature 

 by natural or forced circulation of air over an evaporator located in the 

 room. If the refrigerant used in the mechanical refrigeration system is 

 circulated directly through the evaporator, then the system is referred to 

 as being of the direct type. However, when a secondary cooling medium 

 such as brine is circulated through the evaporator, then the system is of 

 the indirect type. Ammonia is used almost universally in large instal- 

 lations because of its excellent thermodynamic characteristics. However, 

 the use of nontoxic Refrigerant 12 and 22 is increasing. 



The evaporators used consist of bare-pipe coils, finned-pipe coils, 

 refrigerated plates, or blower-type unit coolers. The unit coolers are not 

 satisfactory for storing unpackaged seafoods because of excessive product 

 dehydration resulting from circulation of the air. 



Relative Humidity. To maintain a high relative humidity the temper- 

 ature of the evaporator cooling coils must be as close as possible to the 

 room temperature. If warm moisture-laden air enters the storage room — 

 through cracks in the insulation or by continual opening of the doors — 

 then frost will accumulate on the evaporator surfaces, retarding heat 

 transfer and causing a lower coil and dew point temperature. Widely 

 fluctuating air temperatures within the storage room will also have a 

 similar effect. 



In designing new installations, the temperature of the evaporator coils 

 should be 5 to 10°F lower than the room temperature. Heat transfer 

 from the evaporator coil to the surrounding air is rated in BTU per hour, 

 per square foot of coil surface area, per degree Fahrenheit temperature 

 difference between the coil and the room. Therefore, the difference be- 

 tween coil and room temperature can be decreased proportionally by 

 increasing the evaporator surfaces. 



In conventional designs, economic considerations limit the relative 

 humidity to a range of 70 to 80 per cent. A jacketed-type cold-storage 

 room has been designed, however, for maintaining almost constant room 

 temperatures and relative humidities as high as 90 to 95 per cent. Cana- 



