Refrigerant dryer vs adsorption dryer: when should you switch to adsorption?
A refrigerant dryer covers most industrial applications with a +3 °C pressure dew point. Adsorption goes down to −40 or −70 °C but consumes compressed air. When should you switch?
The difference in one mental picture
A refrigerant dryer cools the compressed air down to +3 °C in a plate heat exchanger, which condenses most of the water vapour; the condensate is then discharged by an electronic condensate drain. It is simple, compact and light on energy, but the pressure dew point is capped at +3 °C, which is enough for most industrial processes but not for demanding ones.
An adsorption dryer passes the air through an adsorbent (activated alumina or molecular sieve). Two towers operate alternately: while one adsorbs, the other regenerates with a share of the dry air, 6% at most on the heatless models of the catalogue, or with the help of an electric heater, which brings that purge down to 3% at most. The result: a pressure dew point down to −70 °C.
When a refrigerant dryer is enough
| Pressure dew point delivered | +3 °C ± 1, stable |
|---|---|
| ISO 8573-1 humidity class | Class 4 (by default) |
| Compressed air consumption | None |
| Typical pressure drop | 0.2 to 0.4 bar |
| Common applications | Mechanical engineering, plastics processing, workshops, painting |
When to switch to adsorption
- Outdoor air network exposed to frost: pressure dew point of −10 / −20 °C minimum
- Pharmaceuticals, food with direct product contact: Class 2 (pressure dew point −40 °C) or 1 (−70 °C)
- Electronics, semiconductors, cleanrooms: Class 1 or 0 (−70 °C)
- Very low temperature processes (cryogenics, industrial cold rooms)
- Pneumatic conveying of hygroscopic powders (cement, milk powder)
The hidden cost of adsorption: purge air
A heatless adsorption dryer regenerates with a share of the air it has just dried: 6% at most on the catalogue models. On a 100 m³/h compressor, up to 6 m³/h never reach the network, along with the compression energy spent on them.
The heat-regenerated version uses an electric heater during regeneration to bring the purge down to 3% at most in the catalogue. It therefore consumes electricity where the heatless version consumes none: in the catalogue, heat-regenerated adsorption dryers carry a power rating of 0.8 to 8 kW, while heatless models carry none. The trade-off lies between that electricity consumption and the compressed air saved on the purge, and it tips all the faster the more hours a year the machine runs.
Put a figure on the purge before choosing: multiply the treated flow by the purge rate, by the specific power of your compressor, then by your annual running hours. The result is the kilowatt hours that regeneration consumes each year, to be compared with the electricity consumption of a heat-regenerated model.
Recommended models for this topic
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Sécheur frigorifique normal (air) 1.5 Nm³/min
1,50 m³/min · 6-10 bar
Voir la fiche →Sécheur frigorifique normal (air) 2.6 Nm³/min
2,60 m³/min · 6-10 bar
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Sécheur adsorption compact (point d'usage) 1.56 m³/min
1,56 m³/min · 4.5-10 bar
Voir la fiche →Sécheur adsorption compact (point d'usage) 2.46 m³/min
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