Cycling Refrigerated Air Dryers, 300 to 1,250 SCFM

A 100 hp screw delivers about 450 SCFM, which the 500 or 510 SCFM size covers at the 100°F rating point. A room that runs hot in summer takes 10 to 20 percent off the dryer's capacity, so the same compressor in a poorly ventilated room belongs on the 550 to 650 SCFM sizes. Measure the room and the aftercooler discharge on a hot afternoon before ordering; guessing low is what puts water in the header in July.

That turns on how long the line idles and how tight the dew point must stay. Stored-cold dryers save the most across long stops, because the refrigeration compressor can rest for the whole gap. At restart, though, the first surge of demand draws the stored cold down quickly and the dew point can rise toward 45°F for a few minutes. If the batch cannot accept that, the digital-scroll dryer from 600 SCFM holds steady through the restart.

After it. The tank evens out the compressor's load and unload pulses, drops some free water and lets the air cool a few degrees before it reaches the exchanger, all of which help a stored-cold dryer hold its charge longer between restarts. Ahead of the receiver the dryer sees full discharge temperature and every pulse, and a unit sized correctly on paper starts passing water at the top of each loading cycle.

Yes. When both can load together, size it to their combined delivery: a 100 hp and a 150 hp at about 450 and 680 SCFM call for the 1,250 SCFM size, not the 1,050. When the smaller machine only runs as a standby, size it to the larger alone, which brings it down to the 800. Load-following refrigeration suits this arrangement well, because the dryer spends most of its hours far below its rating.