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En^ineet'in^ 



COMPRESSOR LOW-SIDE CONTROL ADJUSTMENT FOR HIGH RELATIVE HUMIDITY 



IN CA ROOMS 



In view of the fact that most humidistats presently available are designed 

 to operate in the range of 30-70 per cent relative humid:'.ty and good control at 

 85-90 per cent relative humidity is difficult, a practical solution to maintain 

 at least 85 per cent relative humidity is as follows: 



1. Thoroughly wet down boxes and fruit on loading. 



2. Use mist nozzles to saturate the air as it leaves the refrigeration 

 cooling coils. 



3. Periodically measure R.H. by means of a wet and dry bulb thermometer 

 and operate mist nozzles accordingly. 



4. Adjust the low pressure (suction side) control on the compressor, so 

 that at CA room operating temperatures of 37°F / 1-2°F, the outside 

 surface temperature of the refrigeration cooling coils does not fall 

 below 340F / 1-2 °F. This coil surface temperature will prevent the 

 R.H. from dropping below 85% once it has been attained. The table 

 following gives the suction pressures corresponding to 34°F for the 

 two most commonly used refrigerants in CA rooms. 



Low side gag e pres sure corresponding to 340F . 



Refrigerant 



Freon 12 

 Ammonia 



Theoretical 



31.7 psi 

 50.2 psi 



Allowance for 3° temp. diff. 

 inside to outside of coil 



29.3 psi 

 46.3 psi 



