A compressor used in a multi-box refrigeration system has 4 of its 6 cylinders controlled for variable loads. Assuming that the controlled cylinders are unloaded singly in incremental steps, if two of five boxes are currently feeding, what will be compressor capacity at step 3 of incremental unloading? See illustration GS-RA-13.
⢠Cylinder unloading steps in a 6âcylinder compressor where 4 cylinders are controlled and unloaded one at a time ⢠Relationship between number of active (loaded) cylinders and compressor capacity fraction ⢠Effect of number of evaporators/boxes actually calling for cooling (2 of 5) on how far the capacity control will unload
⢠If there are 6 cylinders total and 4 can be unloaded one by one, how many different loading "steps" are possible, starting from all 6 loaded? ⢠At step 3 of incremental unloading, how many of the 4 controlled cylinders will be unloaded, and therefore how many cylinders will still be doing work? ⢠What fraction is that remaining number of loaded cylinders compared with the fully loaded 6âcylinder capacity, and which choice is closest to that fraction?
⢠Be sure you are counting total loaded cylinders, not just the controlled ones ⢠Confirm that capacity is proportional to the number of loaded cylinders (same stroke and displacement for each) ⢠Verify that your final fraction is written as a decimal matching one of the choices (e.g., 0.833, 0.667, 0.5, 0.333)
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