COLD STORAGE FOR APPLES AND PEARS 23 



Table 3. — Relation of coil-room temperatures to relative humidity in storage room 



Degrees (F.) to which 



Maximum relative humidity when the temperature (° F.) is raised to — 



air is chilled 



24° 26° 



28° 



30° 



32° 



34° 



36° 



38° 



40° 



16... 



Percent 

 68 

 75 

 83 

 91 

 100 



Percent 

 62 

 68 

 76 

 83 

 91 

 100 



Percent 

 57 

 62 

 69 

 75 

 83 

 91 

 100 



Percent 

 52 

 57 

 63 

 69 

 76 

 83 

 91 

 100 



Percent 

 47 

 52 

 57 

 63 

 69 

 76 

 83 

 91 

 100 



Percent 

 43 

 48 

 53 

 58 

 64 

 70 

 77 

 84 

 92 



Percent 

 40 

 44 

 49 

 54 

 59 

 64 

 71 

 78 

 85 



Percent 

 37 

 41 

 45 

 49 

 54 



66 

 72 

 79 



Percent 

 33 



18 



36 



20 



39 



22 



44 



24 



48 



26 



53 



28 





58 



30 







64 



32.... 









70 















Cold-Storage Rooms 



Two general methods are used in the distribution of refrigeration 

 units in cold-storage rooms for apples and pears: (1) Placing refrig- 

 eration pipes on the ceilings and (2) circulating cold air through the 

 rooms. The first is more commonly the direct-expansion system, 

 though cold brine may be pumped through the pipes from a brine 

 cooler. The gradual evolution in the use of refrigeration for fruit 

 from the direct-expansion to the brine-spray system has included the 

 dry-coil bunker system in the intermediate stage. The unit-cooler 

 system is a modification of either the brine-spray or the dry-coil 

 system and is especially convenient for small plants. 



Fruit keeps equally well under any of these systems, provided they 

 are installed so that cooling will be equally fast and temperatures 

 will be kept uniform, with atmospheric humidity at about 85 percent. 

 The choice hinges largely upon economy in installation and oper- 

 ation. 



DIRECT-EXPANSION SYSTEM 



In direct-expansion rooms, that is, where cold ammonia is cir- 

 culated in exposed pipes near the ceiling, the air in contact with 

 the coils becomes cold and, being denser than warm air, moves down- 

 ward. As it picks up heat from the fruit it rises to the pipes to be 

 again cooled. This gravity circulation, caused by differences in air 

 temperatures, results in heat movement by convection. Air veloci- 

 ties in such currents are relatively low, but take place in all parts 

 of the room if the pipes are well distributed over the ceiling, and 

 produce fairly fast cooling. To dispose of the accumulated frost 

 or condensed water the pipes are usually put in groups or banks, and 

 gutters for catching the drip are hung under them, as illustrated in 

 figure 4. 



In rooms where large areas of the ceiling are without coils, direct 

 expansion alone cannot cool the fruit very promptly, and there may 

 be fairly large temperature differences between various parts of the 

 room, even after the fruit has cooled to its final temperature. In 

 such cases, use of either portable or permanent fans operating in 



