01
Separate air condition from material condition
Air psychrometrics describes the gas state. Drying rate also depends on material moisture, surface area, airflow, transfer resistance and time. Storage risk also depends on product and enclosure surface temperatures.
Use the calculator to establish the air-side moisture potential, then apply material-specific limits and measurement practice.
02
Verified air-state examples
At 30 °C/40% RH/101.325 kPa, air contains 10.604 g/kg, has a 14.936 °C dew point and 57.293 kJ/kg enthalpy. At 20 °C/60% RH, it contains 8.736 g/kg with a 12.008 °C dew point.
The warmer air has lower RH yet more water per kg dry air. This is why RH alone cannot rank moisture load across temperatures.
03
Assess condensation risk
Compare dew point with the coldest plausible product, wall, pipe or package surface. At 5 °C/80% RH, dew point is 1.842 °C and humidity ratio is 4.314 g/kg. Moving that air into a warmer space changes RH but not its moisture coordinate unless water transfers.
Use an uncertainty margin and account for thermal bridges, door openings and overnight transients. A room-average probe cannot guarantee every surface is safe.
04
Assess drying direction
Compare inlet and exhaust humidity ratio. Rising exhaust W supports moisture pickup when airflow and sampling are representative. Multiply delta W by verified dry-air mass flow to estimate a water rate, keeping units and time basis explicit.
Do not infer product dryness from air equilibrium alone. Hygroscopic materials require sorption data and an acceptance method appropriate to the product.
05
Limits and next action
The model excludes liquid films, adsorption, biological growth and transient heat/mass transfer. It cannot set a universal safe RH or storage duration.
Next action: calculate inlet and exhaust states at measured pressure, compare humidity ratio and dew point, then document the material-specific criterion used for the actual decision.