Psychrometric Calculator
Calculate comprehensive properties of moist air for HVAC, meteorology, and atmospheric analysis
Calculate Psychrometric Properties
Atmospheric pressure: 1013.3 hPa
Ambient air temperature
Percentage of saturation
🏠 Comfort Assessment
Generally comfortable conditions
Temperature Properties
Humidity Properties
Air Properties
Key Formulas Used
Humidity Ratio: ω = 0.6219 × Pv / (Pa - Pv)
Relative Humidity: φ = Pv / Ps × 100%
Enthalpy: h = 1.006 × Tdb + ω × (2499.86 + 1.84 × Tdb)
Specific Volume: v = 0.287 × (Tdb + 273.15) × (1 + 1.608 × ω) / Pa
Example Calculation
HVAC Design Conditions
Location: Office building at 100m altitude
Dry Bulb Temperature: 25°C (77°F)
Relative Humidity: 60%
Atmospheric Pressure: 1002 hPa
Calculated Properties
1. Saturated vapor pressure at 25°C: 31.69 hPa
2. Partial vapor pressure: 0.6 × 31.69 = 19.01 hPa
3. Humidity ratio: 0.6219 × 19.01 / (1002 - 19.01) = 0.0120 kg/kg
4. Dew point: 16.7°C
5. Enthalpy: 55.5 kJ/kg
Result: Comfortable conditions for office environment
Psychrometric Terms
Dry Bulb Temperature
Ambient air temperature measured by thermometer
Wet Bulb Temperature
Lowest temperature achievable by evaporative cooling
Dew Point
Temperature at which condensation begins
Humidity Ratio
Mass of water vapor per mass of dry air
Comfort Guidelines
Optimal Comfort
20-24°C, 40-60% RH
Acceptable
18-26°C, 30-70% RH
Humidity Issues
<30% or >70% RH
Uncomfortable
<18°C or >26°C
Applications
HVAC system design & control
Industrial drying processes
Agricultural storage conditions
Meteorological analysis
Indoor air quality assessment
Understanding Psychrometric Properties
What is Psychrometry?
Psychrometry is the science of moist air - studying the thermodynamic properties of gas-vapor mixtures. It's essential for HVAC design, industrial processes, and understanding atmospheric conditions.
Key Properties
- •Dry Bulb Temperature: Actual air temperature
- •Wet Bulb Temperature: Adiabatic saturation temperature
- •Dew Point: Saturation temperature at constant pressure
- •Humidity Ratio: Mass of water per mass of dry air
HVAC Applications
Psychrometric calculations are fundamental for designing heating, ventilation, and air conditioning systems. They help determine cooling loads, ventilation requirements, and energy consumption.
Industry Standards
- •ASHRAE (American Society of HVAC Engineers)
- •ISO 7730 (Thermal comfort standards)
- •Psychrometric charts for various pressures
- •Building energy modeling requirements
Mathematical Relationships
ω = 0.6219 × Pv / (Pa - Pv)
Humidity ratio from vapor pressure
φ = Pv / Ps × 100%
Relative humidity definition
h = 1.006×Tdb + ω×(2499.86 + 1.84×Tdb)
Enthalpy of moist air
v = 0.287×(Tdb+273.15)×(1+1.608×ω)/Pa
Specific volume calculation
• 0.6219 (ratio of molecular weights)
• 1.006 kJ/(kg·K) (specific heat of dry air)
• 2499.86 kJ/kg (latent heat at 0°C)
• Pa = atmospheric pressure
• Pv = partial vapor pressure
• Ps = saturated vapor pressure
• Air conditioning load calculations
• Ventilation system design
• Industrial drying processes