Moist Air - Psychrometric Terms

Psychrometry is the science of studying thermodynamic properties of moist air and the use of these to analyze humid air conditions and processes. This tool helps you understand and visualize the key psychrometric properties including dry-bulb temperature, wet-bulb temperature, relative humidity, humidity ratio, specific volume, dew point temperature, and enthalpy.

Calculator

Inputs

Results

Wet-Bulb Temperature-- °C
Dew Point Temperature-- °C
Saturation Pressure-- hPa
Vapor Pressure-- hPa
Humidity Ratio-- kgH₂O/kgair
Specific Volume of Humid Air-- m³/kg
Enthalpy-- kJ/kg

Psychrometric Properties Reference

Dry-Bulb Temperature (Tdb)

The air property most commonly used; measured with a normal thermometer. It determines the sensible heat content in air.

Wet-Bulb Temperature (Twb)

Associated with the moisture content of air. Always lower than dry-bulb temperature except at 100% RH where they are identical.

Relative Humidity (RH)

The ratio of actual water vapor content to maximum possible vapor content at the given temperature and pressure, expressed as a percentage.

Dew Point Temperature (Tdp)

The temperature at which water vapor starts to condense; the temperature at which air becomes completely saturated.

Specific Volume (v)

The space occupied by a unit weight of dry air, expressed in m³/kg or ft³/lb.

Humidity Ratio (x)

The amount of water vapor by weight in dry air, expressed in kgH₂O/kgair or lbH₂O/lbair.

Enthalpy (h)

The measure of total thermal energy in air, expressed per unit weight of air (kJ/kg or Btu/lbair).