Calculate moist air properties including dew point, humidity ratio, and enthalpy for HVAC design and analysis.
Last updated: March 2026 | By Summacalculator
Psychrometrics is the study of the physical and thermodynamic properties of gas-vapor mixtures, most commonly moist air. This field is essential for HVAC (Heating, Ventilation, and Air Conditioning) design, meteorological analysis, and industrial drying processes.
Key properties include dry-bulb temperature (actual air temperature), wet-bulb temperature (cooling effect of evaporation), relative humidity (percentage of saturation), and dew point (temperature at which condensation begins).
The relationships between these properties are governed by thermodynamic laws and are typically displayed on a psychrometric chart. This calculator uses the Magnus formula for vapor pressure and standard ASHRAE equations to compute air properties accurately.
Saturation pressure: es = 0.61078 × exp((17.27 × T) / (T + 237.3)) kPa
Actual vapor pressure: e = RH × es
Humidity ratio: w = 0.62198 × (e / (P - e)) kg/kg
Enthalpy: h = 1.006 × T + w × (2501 + 1.86 × T) kJ/kg
Calculate air properties for a typical summer day with 30°C dry-bulb temperature and 60% relative humidity at sea level pressure.
The comfort zone is the range of temperature and humidity (typically 20-25°C and 30-60% RH) where most humans feel comfortable. HVAC systems are designed to maintain conditions within this zone.
Lower barometric pressure at higher altitudes increases the humidity ratio for the same relative humidity, as air can 'hold' more moisture relative to its mass. Always adjust pressure for altitude in HVAC calculations.
As sweat evaporates, it absorbs latent heat from your skin (enthalpy transfer), lowering your body temperature. This cooling is less effective in high humidity because evaporation slows when the air is already saturated.
It is a graphical representation of all air properties. If you know any two independent properties (like dry bulb and RH), you can find all others on the chart. Digital calculators like this one replace the manual chart reading process.
Dew point is the temperature at which condensation begins. Wet-bulb temperature is the lowest temperature achievable by evaporative cooling. Wet-bulb is always between dry-bulb and dew point temperatures.
Enthalpy represents the total energy content of air (sensible + latent heat). It's used to calculate cooling loads, size equipment, and determine energy requirements for air conditioning and dehumidification.
Theoretically yes, creating supersaturated air, but it's unstable and quickly condenses into fog or clouds. In practice, 100% RH is the maximum for stable air at a given temperature.
This calculator uses the Magnus formula and ASHRAE standard equations, providing accuracy within ±0.5°C for dew point and ±2% for humidity ratio in the range of -20°C to 50°C, suitable for most HVAC applications.
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