Refrigerated and Desiccant Air Dryer Sizing

Typically 100 psig inlet, 100 degF inlet air, 100 degF ambient -- and a plant almost never sits at all three. Every correction runs the same way: hotter inlet air carries far more water and derates the dryer, lower pressure means more actual volume per unit mass and derates it, and a hotter ambient hurts the condenser and derates it again. BECAUSE THEY MULTIPLY, three individually modest factors compound: 0.80 times 1.10 times 0.95 is 0.836, so a 200 scfm nameplate delivers only 167 scfm and the honest requirement is 239. A dryer selected on its badge number is the reason water comes out of the drops. The choice between refrigerated and desiccant is a DEW POINT decision, not a capacity one. A refrigerated dryer holds roughly a 35 to 40 degF pressure dew point and cannot go below freezing without icing, so anything running outdoors, feeding an unheated line, or supplying instrument or breathing air needs desiccant. The cost of desiccant is the purge: a heatless regenerative dryer diverts around 15% of its own throughput to regenerate the offline tower, and that purge is real compressor capacity which must be ADDED to the compressor sizing rather than subtracted from the dryer's -- delivering 200 scfm to the plant through a 15% purge means the compressor supplies 235. This applies correction factors the user takes from the manufacturer's own tables; it does not supply them, because they differ by model and by dryer technology and a generic table is the thing that goes stale. It does not select a dryer, determine the required pressure dew point for the application, or evaluate whether a refrigerated unit will ice; it does not size the pre-filters and after-filters that a desiccant bed requires and without which the bed is destroyed by oil carryover; and it does not address drain traps, which are where most compressed-air moisture problems actually originate. It does not compute the moisture load itself. The dryer manufacturer's correction tables and dew point ratings, and the requirements of the air application, govern.

the inlet temperature, operating pressure and ambient correction factors MULTIPLY: corrected capacity = rated x their product, and required rating = actual flow / their product; a regenerative desiccant dryer's compressor load = actual flow / (1 - purge fraction).

The compressed-air dryer correction-factor method as standard practice, by name, with the factors taken from the dryer manufacturer's OWN tables because they differ by model and technology. A refrigerated dryer holds roughly a 35 to 40 degF pressure dew point and cannot go below freezing without icing. The dryer manufacturer's correction tables and dew point ratings, and the requirements of the air application, govern.

A product of correction factors the user reads off the manufacturer's table; no factor table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: actual_scfm, temp_correction, pressure_correction, ambient_correction, candidate_rated_scfm, purge_fraction, combined_factor, required_rated_scfm, candidate_delivers_scfm, purge_scfm, compressor_load_scfm

• Correction factors are entered, not supplied they differ by model and by dryer technologythe dryer manufacturer's tables
• Pre- and after-filters are not sized and oil carryover destroys a desiccant bedthe dryer manufacturer's data
• Drain traps are not addressed and they are where most compressed-air moisture problems originatecompressed air practice