Refrigerated vs Desiccant Air Dryer Selection Guide
The real question is how dry your air needs to be in your conditions, and how much air you have left for production after the dryer. Use this worksheet to compare dryer quotes fairly.
1. Decide how dry the air needs to be
Pressure dew point is the temperature where water condenses out of the air at line pressure. It isn’t the same as atmospheric dew point. Say where it’ll be measured and the pressure there; a reading taken after the air expands has to be converted.
Compare your coldest pipe or process temperature with the dew point you need. A refrigerated dryer (dew point above freezing) is often fine indoors, but not where pipes go below freezing. When you need much drier air, look at a desiccant dryer.
| Decision | Refrigerated | Desiccant adsorption |
|---|---|---|
| Moisture removal | Cools air so water condenses and is drained. | Adsorbs water vapor; the desiccant must be regenerated. |
| Typical PDP reference | Pneumatech’s overview describes approximately +2 to +10°C, depending on equipment and conditions. | The PH 230–635 HE family lists −40°C (−40°F), with a dedicated −70°C (−94°F) option. |
| Operating load | Compare refrigeration power, controls at part load, ambient limits and drains. | Compare purge flow, regeneration heaters/blowers where used, switching and controls. |
| Maintenance | Keep condenser/heat exchanger and drains working; trend temperature and differential pressure. | Maintain prefilters/afterfilters, desiccant, switching valves, exhaust silencers and dew-point controls. |
These are typical figures, not guaranteed dew points for every site. Choose based on the manufacturer’s rating conditions and your process spec. OEM dew-point explanation and PH model source.
2. Correct the rating for your real conditions
- Write down the most air the dryer will see, your lowest operating pressure, the hottest inlet air, and the hottest room or cooling-water temperature. Note the conditions your flow figure is based on.
- Get the manufacturer’s correction table. Check whether you multiply the rating by the factors or divide your flow by them; makers do it differently.
- If the factors multiply the rating, usable capacity = nominal rating × combined correction factor. Just as an example, if the combined factor were 0.75, 200 SCFM of inlet air would need a dryer rated at least 200 / 0.75 = 266.7 SCFM. The 0.75 is made up, not a real manufacturer’s factor.
- Separately check maximum pressure, allowed pressure drop, electrical supply and any cooling-water needs. The CFM on the label doesn’t tell you how it performs in summer.
3. How much air the dryer uses (purge)
Heatless desiccant dryers use some of the dried air to regenerate (purge). Other types use less air but add heaters, blowers and controls. Ask for the actual model’s purge rate, cycle and part-load operation instead of using one percentage for every desiccant dryer.
Illustrative air balance: if production needs 200 SCFM and purge is 15% of the air going into the dryer, the dryer needs 200 / (1 - 0.15) = 235.3 SCFM in. That’s 35.3 SCFM of purge. The 15% is just an example, not a Pneumatech rating. If the maker measures purge against outlet flow, the math changes.
Your compressor has to supply that extra air at pressure. If your measured plant flow already includes purge, don’t add it again. Ask whether dew-point control cuts purge when moisture is low, how it’s measured, and what happens if the sensor fails. Pneumatech’s PH family offers optional dew-point control and purge nozzle tuning; confirm what’s on the unit you order.
4. Compare operating costs the same way
Use your yearly operating hours, how loaded the system is, your electricity rate and the compressor’s power use at your pressure. Add up dryer power (refrigeration, heater or blower), the extra compressor power for purge, and the cost of pressure drop, without counting anything twice.
| Input to request | Why it changes the decision |
|---|---|
| Rated and corrected inlet capacity | Reconciles the brochure flow with the actual site. |
| Guaranteed PDP and test location | Defines acceptance under specified conditions. |
| Net usable air and purge basis | Shows what remains for production. |
| Part-load controls and auxiliary kW | Avoids judging only full-load electrical draw. |
| Filter/dryer pressure drop, clean and service limits | Allows evaluation of pressure and maintenance cost. |
| Service items and planned downtime | Includes desiccant, valves, filtration, drains and refrigeration service. |
For a rough number, multiply the extra SCFM for purge by your compressor’s kW per SCFM at pressure. Controls and part-load efficiency change the result. Ask the vendor for an operating cost estimate; this guide doesn’t promise any savings or payback.
5. Check performance and track down water
- Agree how you’ll test it: load, pressure, temperatures, where you measure, with what, and how long it runs first. Log dew point and pressure drop under normal demand.
- If water shows up downstream, check the drains, separator, bypass valve, overloading, hot inlet air and low pressure before you assume the dryer needs replacing.
- On desiccant dryers, check regeneration, valve switching, contamination and sensors using the manufacturer’s steps. On refrigerated dryers, check cooling, drains and temperature limits.
- Dry air isn’t necessarily clean air. Oil and particle filtration are separate.
Use the installation checklist for power and site prep. We can look at equipment and treatment requirements, measured system performance and maintenance scope. Send your flow, pressure, target dew point, hottest and coldest conditions, schedule and current dryer model.
Common questions
Is a desiccant dryer always the better choice?
No. Pick based on how dry your process needs the air and your coldest pipes, then compare corrected capacity, air used, energy and maintenance.
Can I size a dryer from the compressor horsepower?
No. Use your actual flow, pressure, temperatures and the manufacturer’s correction factors and limits.
Does the purge example apply to every desiccant dryer?
No. It’s just math with an assumed number. Get the real model’s purge rate, how it’s measured, how it regenerates and its controls.
Sources
Checked October 22, 2026. For your project, go by the current data sheet and installation manual for the exact model.
Discuss your project requirements
Send your site ZIP and whatever requirements you have. We’ll tell you what fits. Call (844) 310-8665 or email [email protected].