Psychrometric Calculator
Evaluate moist air properties from dry-bulb temperature, relative humidity, and pressure.
Air Properties Calculator
Humidity Ratio
9.881
g/kg dry air
Relative Humidity
50.0
%
Dew Point
13.9
°C
Wet-Bulb Temp
17.8
°C
Enthalpy
50.32
kJ/kg
Specific Volume
0.8580
m³/kg
Formula Block (Live Values)
Psychrometrics: The Science of Moist Air
Psychrometrics is the study of the thermodynamic properties of moist air — a mixture of dry air and water vapor. Understanding these properties is essential for HVAC system design, cooling tower sizing, grain drying, and industrial process control. This calculator uses the Hyland-Wexler equations for saturation pressure over water, which are the ASHRAE standard formulation.
The humidity ratio (W) is the mass of water vapor per unit mass of dry air. Relative humidity is the ratio of the actual vapor pressure to the saturation vapor pressure at the same temperature. The dew pointis the temperature at which air becomes saturated and condensation begins. The wet-bulb temperature is the temperature read by a thermometer covered in water-soaked cloth over which air is passed, and it approximates the lowest temperature achievable by evaporative cooling.
FAQ: Psychrometric Calculations
Dry-bulb is the actual air temperature. Wet-bulb is the temperature a thermometer reads when its bulb is wrapped in wet cloth and exposed to moving air — it reflects evaporative cooling potential.
Atmospheric pressure affects the boiling point of water and the saturation vapor pressure. At higher altitudes (lower pressure), air can hold less moisture for the same humidity ratio.
The enthalpy difference between outdoor and indoor air determines the total cooling or heating load. Coil sizing and energy consumption calculations rely on this value.
Example: Summer Air Conditioning Load
Outdoor air: 35°C, 60% RH → h ≈ 90.4 kJ/kg
Indoor setpoint: 24°C, 50% RH → h ≈ 47.8 kJ/kg
The overall enthalpy payload difference equates to 42.6 kJ/kg. For each 1 kg/s of total active mass airflow passing across your evaporator coil matrix, this yields a continuous cooling requirement profile of exactly 42.6 kW.