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Compressed Air Moisture Calculator

Calculate condensate produced at each stage of a compressed air system — aftercooler and dryer. Determine pressure dew point and atmospheric dew point for air quality specification.

Ambient Conditions
%
m

P_atm = 101.3 kPa

Compressor & Treatment

Typically ambient + 8-15°C (air-cooled) or + 5-8°C (water-cooled)

Results
Inlet humidity ratio11.89 g/kg
Inlet atm. dew point16.6 °C
Inlet moisture rate54.7 L/hr

Aftercooler

Temperature35.0 °C
Humidity ratio4.40 g/kg
Condensate34.5 L/hr
Pressure dew point35.0 °C
Atmospheric dew point2.1 °C
Total condensate34.5 L/hr
Total condensate827.4 L/day

About Compressed Air Moisture

Ambient air always contains water vapor. When this air is compressed to typical industrial pressures (7-13 bar), the same mass of water vapor occupies a much smaller volume. Since the air can only hold a limited amount of moisture at any given temperature and pressure, the excess condenses as liquid water. A typical 60 Nm³/min compressor operating at 7 bar in warm, humid conditions can produce over 500 litres of condensate per day.

Aftercoolers

Most compressors include an aftercooler that cools the compressed air from the high discharge temperature (80-200°C depending on compressor type) down to a practical temperature, typically 8-15°C above the cooling medium temperature. This is where the majority of condensate is removed. A moisture separator and automatic drain downstream of the aftercooler collect the liquid water before it enters the distribution system.

Dryers

For applications requiring dry air (painting, pneumatic instruments, food processing, pharmaceuticals), a dryer is installed downstream of the aftercooler. Refrigerated dryers cool the air to approximately 3°C pressure dew point, removing most remaining moisture at modest energy cost. Desiccant dryers use adsorption to achieve pressure dew points of -40°C or lower, required for critical applications and outdoor piping in freezing climates.

Pressure Dew Point vs Atmospheric Dew Point

The pressure dew point (PDP) is the temperature at which compressed air becomes saturated at line pressure. The atmospheric dew point (ADP) is the equivalent at ambient pressure — it is always lower than the PDP because at lower pressure the air can hold more moisture. ISO 8573-1 air quality classes reference pressure dew point for specifying compressed air dryness.

For moisture condensation in pipes carrying warm air through cold environments, see our pipe condensation calculator. For pipe insulation heat loss analysis, use the insulation thickness calculator. For full pipe network simulation, try SimuPipe.

Frequently Asked Questions

How much condensate does a compressor produce?
A typical 60 Nm3/min compressor operating at 7 bar in warm, humid conditions (30 degrees C, 80% RH) can produce over 500 litres of condensate per day. The exact amount depends on inlet air temperature and humidity, compressor discharge pressure, aftercooler outlet temperature, and dryer type. This calculator shows the condensate produced at each treatment stage.
What is pressure dew point and why does it matter?
Pressure dew point (PDP) is the temperature at which compressed air becomes saturated at line pressure. If any point in your distribution system drops below the PDP, condensation will occur. ISO 8573-1 uses PDP to classify compressed air quality. For example, Class 4 requires PDP of 3 degrees C or lower (typical refrigerated dryer), while Class 1 requires -70 degrees C (desiccant dryer).
What is the difference between a refrigerated and desiccant dryer?
Refrigerated dryers cool compressed air to about 3 degrees C PDP, condensing most moisture. They are energy-efficient and suit general industrial use. Desiccant dryers use adsorption media to achieve PDP of -40 degrees C or lower, required for critical applications (instruments, painting, food processing) and outdoor piping in freezing climates. Desiccant dryers consume more energy, typically 10-15% of compressor output for purge air.
How does altitude affect compressed air moisture?
Higher altitude means lower atmospheric pressure and typically lower absolute humidity in the intake air. At 1000 m elevation, atmospheric pressure drops to about 89.9 kPa, which changes the moisture capacity of the air. This calculator adjusts for altitude using the standard atmosphere model, ensuring accurate condensate and dew point predictions for installations at any elevation.
What happens if I don't remove moisture from compressed air?
Moisture in compressed air causes corrosion in pipes, cylinders, and tools; washes lubricant from pneumatic equipment; damages instruments and control valves; ruins paint finishes in spray applications; contaminates products in food and pharmaceutical manufacturing; and causes ice blockages in outdoor lines during cold weather. Proper moisture removal with aftercoolers and dryers prevents these costly problems.

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