Enthalpy Calculator

The Enthalpy Calculator determines the total heat content of moist air, combining sensible and latent heat components. Essential for HVAC design, energy analysis, and psychrometric calculations.

Modify the values and click the calculate button to use
Input Method
Dry Bulb Temperature °C
Relative Humidity %
Atmospheric Pressure kPa
Temperature Unit  
Output Units

Related Psychrometric Calculator | Relative Humidity Calculator | Dew Point Calculator

Understanding Enthalpy

Enthalpy is the total heat content of moist air, representing the sum of sensible heat (temperature-related) and latent heat (moisture-related) components. It's a fundamental property in HVAC design and energy analysis.

Enthalpy Components

Sensible Heat

Definition: Heat associated with temperature change

Formula: hsensible = cp × T

Where:

  • cp = specific heat of dry air (≈ 1.006 kJ/kg·°C)
  • T = dry bulb temperature (°C)

Latent Heat

Definition: Heat associated with moisture content

Formula: hlatent = W × hfg

Where:

  • W = humidity ratio (kg water/kg dry air)
  • hfg = latent heat of vaporization (≈ 2501 kJ/kg at 0°C)

Total Enthalpy Formula

Complete Formula

h = cp × T + W × (hfg + cpw × T)

Simplified (at standard conditions):

h = 1.006 × T + W × (2501 + 1.86 × T)

Where:

  • h = specific enthalpy (kJ/kg dry air)
  • T = dry bulb temperature (°C)
  • W = humidity ratio (kg/kg)
  • cpw = specific heat of water vapor (≈ 1.86 kJ/kg·°C)

HVAC Applications

Cooling Load Calculations

Air Mixing Calculations

System Performance

Typical Enthalpy Values

Condition Temperature (°C) RH (%) Enthalpy (kJ/kg)
Winter Indoor 20 40 35.6
Summer Indoor 24 50 47.7
Hot Humid Outdoor 35 70 100.8
Cold Dry Outdoor -10 80 -7.2

Psychrometric Processes

Sensible Heating

Sensible Cooling

Cooling and Dehumidification

Humidification

Energy Analysis

Cooling Energy Calculation

Cooling Load = ṁ × (hentering - hleaving)

Where:

  • ṁ = mass flow rate of air (kg/s)
  • hentering = enthalpy of air entering coil (kJ/kg)
  • hleaving = enthalpy of air leaving coil (kJ/kg)

Heating Energy Calculation

Heating Load = ṁ × (hleaving - hentering)

For sensible heating:

Heating Load = ṁ × cp × (Tleaving - Tentering)

Unit Conversions

From To Multiply by
kJ/kg Btu/lb 0.4299
Btu/lb kJ/kg 2.326
kJ/kg kcal/kg 0.2388

Measurement and Instrumentation

Direct Measurement

Calculated Values

Accuracy Considerations

Measurement Errors

Calculation Precision

Software and Tools

Psychrometric Software

Design Applications

Note: Enthalpy calculations assume ideal gas behavior and standard atmospheric composition. For high-precision applications or extreme conditions, consider using more detailed psychrometric equations and property correlations.