Calculator
EngineeringPsychrometric Calculator
Free online psychrometric calculator for HVAC calculations. Calculate relative humidity, dew point, wet bulb temperature, enthalpy, and other air properties based on dry bulb temperature and humidity.
What is a Psychrometric Calculator?
A psychrometric calculator is an HVAC engineering tool that determines the thermodynamic properties of moist air. Given dry bulb temperature and one humidity parameter (such as relative humidity, wet bulb temperature, or dew point), it calculates all other psychrometric properties including enthalpy, humidity ratio, specific volume, and vapor pressure. These calculations are essential for HVAC system design, air conditioning load calculations, and indoor air quality management. The calculator implements the same principles as a psychrometric chart but provides precise numerical values.
Psychrometric Properties Explained
- Dry Bulb Temperature (DBT): The actual air temperature measured by a standard thermometer
- Wet Bulb Temperature (WBT): Temperature measured with a wet cloth covering the thermometer bulb, accounting for evaporative cooling
- Dew Point Temperature: Temperature at which air becomes saturated and water vapor begins to condense
- Relative Humidity (RH): Ratio of actual water vapor to maximum possible at given temperature (percentage)
- Humidity Ratio: Mass of water vapor per unit mass of dry air (g/kg or lb/lb)
- Specific Enthalpy: Total heat content of moist air per unit mass (kJ/kg or BTU/lb)
- Specific Volume: Volume of moist air per unit mass of dry air (m³/kg or ft³/lb)
- Vapor Pressure: Partial pressure of water vapor in the air mixture
Key Psychrometric Equations
- Saturation Pressure: Pws = exp(77.345 + 0.0057T - 7235/T) / T^8.2
- Humidity Ratio: W = 0.622 × Pw / (P - Pw)
- Enthalpy: h = 1.006T + W(2501 + 1.86T) kJ/kg
- Relative Humidity: RH = Pw / Pws × 100%
- Dew Point: Inverse of saturation pressure equation at RH=100%
Common Applications
- HVAC system design: Sizing cooling and heating equipment
- Cooling load calculations: Determining sensible and latent heat loads
- Dehumidification: Designing moisture removal systems
- Humidification: Calculating water addition requirements
- Air mixing: Determining properties of mixed air streams
- Energy recovery: Analyzing heat and moisture transfer
- Industrial processes: Drying, conditioning, and climate control
- Indoor air quality: Managing comfort and preventing condensation
- Data center cooling: Precision environmental control
Usage Tips
- Standard conditions: 20-25°C dry bulb, 40-60% RH for comfort
- Cooling mode: Process moves air from warm/humid to cool/dry
- Heating mode: Air typically becomes drier (lower RH) when heated
- High altitude: Lower atmospheric pressure affects calculations
- Dew point below 10°C: Low risk of mold and condensation
- Enthalpy difference: Drives cooling/heating energy requirements
- Summer design: Typically 35°C DB, 24°C WB for outdoor air
- Winter design: Varies by climate, often -10 to 5°C with low humidity
