COLD STORAGE FOR APPLES AND PEARS 



57 



During the cooling period, when the refrigerating equipment is 

 operating to full capacity, the volume of air circulation may be 

 considered in balance if the temperature difference between deliv- 

 ery and return air does not exceed 10° F. A lower split is desir- 

 able, but if it is greater than 10° an increased volume of air cir- 

 culation will be found beneficial. As the load is cooled down and 

 as less warm fruit is brought in, the split will decrease and should 

 reach 1° to 2°. After fruit temperatures become about stationary, 

 a split exceeding 1.5° is an indication of insufficient air volume. Dur- 

 ing this period further cooling is not required, but it is necessary 

 to maintain uniform temperatures throughout the room. 



Uniformity of temperature depends first on an adequate volume 

 of air. If the volume is sufficient, as indicated by the split between 

 delivery and return, and if temperatures in some parts of the room 

 are still too high, the air is not being distributed to best advantage. 

 This may sometimes be corrected by readjusting the delivery or re- 

 turn openings, giving special attention to increasing the volume of 

 air entering the return ducts near the points of highest temperature. 



AMMONIA PRESSURES 



Koutine observation of the gage pressures on the refrigeration equip- 

 ment should be made. Too low suction pressures or too high head 

 pressures are signs that the system needs attention. Ordinarily suc- 

 tion pressures below 20 to 25 pounds indicate that the cooling coils 

 are not picking up heat as rapidly as they should. Head pressures 

 of over 160 to 170 pounds indicate lack of sufficient cooling in the 

 condenser. These limits depend upon the kind of system used, but 

 the cause of any unexpected changes in pressure should be found 

 and corrected. If pressures are normally outside the above limits 

 the possibility of making adjustments or changes in the installation 

 should be investigated in order to reduce power consumption and 

 get more refrigeration. Table 9 shows how power consumption in- 



Table 9. — Relation of head or condensing and suction pressures to horsepower 

 requirements per ton for typical ammonia compressors 



6- BY 6-INCH COMPRESSOR 







Condensing pressure (pounds) 



Suction pressure 



of— 





10 pounds 



20 pounds 



25 pounds 



30 pounds 



35 pounds 



85 -- 



1.30 

 1.42 

 1.62 

 1.75 

 1.94 

 2.12 

 2.29 



0.90 

 1.04 

 1.18 

 1.33 

 1.47 

 1.60 

 1.76 



0.77 

 .90 

 1.03 

 1.17 

 1.31 

 1.44 

 1.57 



0.66 

 .79 

 .91 

 1.03 

 1.17 

 1.30 

 1.42 



0.56 



105 



.68 



125 



.82 



145 



.93 



165 



1.05 



185 



1.17 



205 __- --- 



1.29 







9- BY 9-INCH COMPRESSOR 







85 . 



1.20 

 1.32 

 1.50 

 1.67 

 1.83 

 2.00 

 2.17 



0.84 

 .97 

 1.11 

 1.25 

 1.39 

 1.53 

 1.67 



0.71 

 .84 

 .97 

 1.10 

 1.23 

 1.36 

 1.50 



0.61 

 .73 

 .86 

 .98 

 1. 11 

 1.23 

 1.36 



0.52 



105-. 



.64 



125 . 



.77 



145 



.88 



165 



1.00 



185 



1.11 



205 



1.24 







