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Quotes - Engineering - SalesSizing an Aftercooler
IPAC aftercoolers are catalogued by SCFM at a stated set of conditions, and sizing is a matter of correcting your conditions to theirs.
The published ratings assume compressed air at 100 PSIG entering at 250°F, which is typical of a two-stage rotary screw. The A Series air-cooled table then assumes a 75°F ambient and cools to within 15°F of it; the water-cooled tables assume 80°F inlet water and give the water flow in GPM needed to reach the series approach. A single-stage reciprocating compressor may discharge at 350°F and needs a larger unit or more water for the same SCFM - the water-cooled part pages list the GPM at 200, 300 and 400°F inlet for that reason.
Rule of Thumb
Before the calculation.
- About 4 SCFM per compressor horsepower for a rotary screw
- About 1 GPM of 80°F water per 100 SCFM on a water-cooled unit at 250°F inlet
- Air-cooled: pick the model whose compressor HP column matches
- When in doubt, one size up costs less than a wet air system
Start With the Compressor, Not the Horsepower
Start with the compressor's rated delivery in SCFM at its working pressure, not the nameplate horsepower alone; the catalogue's horsepower column is a guide, not a rating. Then fix the cooling medium: room air temperature on the hottest day for an air-cooled unit, or the warmest cooling water of the year for a shell and tube. Then decide the outlet temperature the plant needs - within 15°F of the room is fine for shop air, but a refrigerated dryer or a paint line is better served by the 59 Series approach.
Check the Pressure Class
Finally, check the pressure class. Standard units are 200 PSIG; the small NPT water-cooled models are 300 PSIG; anything higher, or any unit that must be U-stamped, CRN-registered or PED-marked, is specified at the time of order.
| RANGE | TYPE | COVERS | RATING |
| Air-Cooled Aftercoolers | Air-Cooled Aftercooler | Fifteen catalogued sizes from 30 to 2,800 SCFM, matched to compressors from 5 to 700 horsepower | 200 PSIG / 400°F |
| Water-Cooled 51 Series | Water-Cooled Aftercooler | Fifteen shell and tube models from 38 to 4,785 SCFM, all 51-1/8 inches long | 200 PSIG (300 PSIG small NPT units) |
| Water-Cooled 59 Series | Water-Cooled Aftercooler | Nineteen close-approach models from 37 to 11,970 SCFM, all 59 inches long | 200 PSIG (300 PSIG small NPT units) |
Common FAQs
As a first guess only - about 4 SCFM per horsepower on a rotary screw. The catalogue's horsepower column is a guide; the rating is in SCFM at 100 PSIG and 250°F inlet, and that is the figure to match.
Yes. Single-stage reciprocating machines run hot, and the water-cooled tables list the GPM needed at 200, 300 and 400°F inlet for that reason. Expect more water or one size larger for the same SCFM.
The warmest of the year. An aftercooler sized on winter tower water will deliver wet air in August. For an air-cooled unit use the room temperature on the hottest day.
Related Pages
Approach Temperature: 51 vs 59
What approach temperature means for a water-cooled aftercooler, and when the IPAC 59 Series 5-10 F approach is worth choosing over the 51 Series 15-20 F approach.
READ
Air-Cooled Aftercoolers
Fifteen catalogued sizes from 30 to 2,800 SCFM, matched to compressors from 5 to 700 horsepower.
READ
Water-Cooled 51 Series
Fifteen shell and tube models from 38 to 4,785 SCFM, all 51-1/8 inches long.
READ
