Formula
Pw_line × P_atm = Pw_atm × P_line (partial pressure of water scales with total pressure)Dryer ratings list pressure dewpoint (PDP) at line pressure. Instrument and outdoor air specs are often quoted as atmospheric dewpoint (ADP) at 0 psig. ADP is always colder than PDP at the same line.
Atmospheric dewpoint (at 0 psig)
-4.6°F
-20.3 °C
Reference points
- Refrigerated dryer at 100 psig, 38°F PDP ≈ 1°F ADP.
- Desiccant dryer at 100 psig, –40°F PDP ≈ –68°F ADP.
- Desiccant –100°F PDP ≈ –123°F ADP — meets ISO 8573 Class 2 humidity.