450 BELL SYSTEM TECHNICAL JOURNAL 



vantages from storage due to the elimination of lead press changes, it 

 was decided that a minimum moisture condition of .5 of one per cent 

 with storage periods not greater than 24 hours would result in minimum 

 conductance and capacitance values consistent with manufacturing 

 costs. The limit of .5 of one per cent was decided upon since to main- 

 tain humidities lower than that, costs would increase very rapidly and 

 entirely out of proportion to the change in relative humidity conditions 

 and the final result. 



The air conditioning equipment installed at the Baltimore plant is 

 unique, in that a relative humidity of .5-.8 per cent is maintained at a 

 temperature of 100° F. without resorting to refrigeration. Silica gel, 

 highly porous form of silicon dioxide, or sand, is used as the water 

 absorptive medium. Before deciding upon this method of dehydration 

 other existing types of equipment were investigated. To obtain such 

 low humidities with the usual types of dehumidification systems would 

 require more than one stage of cooling and result in more expensive 

 operation costs in comparison with silica gel units. 



The design requirements of this equipment were based on data 

 established for the following: 



(1) Heat losses in the walls and infiltration of moisture. 



(2) The movement into the storage room of core trucks filled with dry 



cable at temperatures of approximately 260° F., and the incident 

 rush of storage room air into the vacuum driers when the 

 vacuum was broken. 



(3) The loss of conditioned air when cables are being pulled through 



the bell mouth openings to the press and also when the storage 

 room doors are opened. 



(4) The actual moisture content of outside air, which must be dried to 



replace losses in the storage room. 



Based on a summary of the B.T.U. losses and gains which could be 

 expected in the manufacturing process, a study of the Baltimore tem- 

 perature conditions over a period of years, and an analysis of the 

 humidity conditions which would be encountered, equipment was de- 

 signed which will handle a volume of 13,000 cu. ft. of air per minute 

 amounting to a complete change of room air five times per hour. Of 

 this total amount approximately 10,300 cu. ft. is re-circulated, cooled, 

 dehydrated and brought back to the storage room requiring adsorber 

 capacity for only .6 pound of water per minute. Twenty-six hundred 

 cu. ft. of air is drawn from the outside to compensate for air losses at 

 various points in the room and to maintain an overall room pressure of 

 about \ ounce in excess of outside air pressures, requiring additional 

 adsorber capacity of approximately 4 jjounds of water per minute. 



