Making Psychrometrics Simple
Psychrometrics is the study of air-water mixtures and their properties. Understanding these relationships is crucial for designing efficient HVAC systems, controlling indoor comfort, and solving various engineering challenges related to humidity and temperature control.
What You'll Discover
This tool isn't just another calculator—it's your visual playground for exploring how air behaves under different conditions. Whether you're designing HVAC systems, studying building science, or just learning about psychrometrics, our interactive chart helps you visualize and understand complex air property relationships.
- Evaluate air state and specify the following parameters:
- Multi-step air process calculation including Heating, Cooling, Humidification and Mixing
- Air state and process visualization on the psychrometric chart
- Support for both SI (metric) and IP (imperial) unit systems
| Parameter | Symbol | SI Unit | IP Unit |
|---|---|---|---|
| Dry Bulb Temperature | Tdb | °C | °F |
| Wet Bulb Temperature | Twb | °C | °F |
| Dew Point Temperature | Tdew | °C | °F |
| Humidity Ratio | W | kg/kgda | lb/lbda |
| Relative Humidity | RH | % | % |
| Specific Enthalpy | h | kJ/kgda | Btu/lbda |
| Density | ρ | kg/m3 | lb/ft3 |
| Dry Air Mass Flow Rate | ṁda | kg/s | lb/h |
| Volumetric Flow Rate | V̇ | m3/s | cfm |
Quick Start Guide
Follow these simple steps to solve your first psychrometric problems.
Sensible Heating of Moist Air
Scenario: Moist air, saturated at 2°C, enters a heating coil at a rate of 10 m³/s. Air leaves the coil at 40°C. Find the required rate of heat addition.
In sensible heating, the air temperature increases while the humidity ratio remains constant. This process moves horizontally from left to right on the psychrometric chart.
- Set Initial State:
- Pressure [Pa]: 101325.0
- Dry-bulb Temperature [°C]: 2
- Relative Humidity [%]: 100.0
- Volumetric Flow Rate [m³/h]: 36000.0
- Press "Set Initial State" Button
- Set Process 0→1:
- Process Type: Heating
- Input Type: ΔT
- ΔT [°C]: 38
- Press "Apply Process" Button
- The required heating capacity is presented in the results table
Solution: The required heating capacity is approximately 491 kW.
Psychrometric Process Visualization
Point 0: Initial air state (2°C, 100% RH)
Point 1: Final air state (40°C, 9.6% RH)
The horizontal line represents constant humidity ratio during heating.
Cooling and Dehumidification of Moist Air
Scenario: Moist air at 30°C dry-bulb temperature and 50% rh enters a cooling coil at 5 m³/s and is processed to a final saturation condition at 10°C. Find the kW of refrigeration required.
In this process, the air is cooled below its dew point temperature, causing moisture to condense out. The resulting air has both a lower temperature and lower humidity ratio.
- Set Initial State:
- Pressure [Pa]: 101325.0
- Dry-bulb Temperature [°C]: 30
- Relative Humidity [%]: 50.0
- Volumetric Flow Rate [m³/h]: 18000.0
- Press "Set Initial State" Button
- Set Process 0→1:
- Process Type: Cooling
- Input Type: ΔT
- ΔT [°C]: 20
- Press "Apply Process" Button
- The required cooling capacity is presented in the results table
Solution: The refrigeration required is approximately 199 kW.
Psychrometric Process Visualization
Point 0: Initial air state (30°C, 50% RH)
Point 1: Final air state (10°C, 100% RH)
Adiabatic Mixing of Two Moist Airstreams
Scenario: A stream of 2 m³/s of outdoor air at 4°C dry-bulb temperature and 2°C thermodynamic wet-bulb temperature is adiabatically mixed with 6.25 m³/s of recirculated air at 25°C dry-bulb temperature and 50% rh. Find the dry-bulb temperature and thermodynamic wet-bulb temperature of the resulting mixture.
In this process, two airstreams with different properties are mixed, resulting in a new air state with intermediate properties. The final state is determined by an energy and mass balance between the two streams, with the mixing point lying on a straight line connecting the two initial states on the psychrometric chart. The position of the mixing point on this line depends on the mass flow rates of the two streams.
- Set Initial State:
- Pressure [Pa]: 101325.0
- Dry-bulb Temperature [°C]: 4.0
- Wet-bulb Temperature [°C]: 2.0
- Volumetric Flow Rate [m³/h]: 7200
- Press "Set Initial State" Button
- Set Process 0→1:
- Process Type: Mixing
- Dry-bulb Temperature [°C]: 25.0
- Volumetric Flow Rate [m³/h]: 22500
- Relative Humidity [%]: 50.0
- Press "Apply Process" Button
- The resulting dry-bulb temperature and wet-bulb temperature of the mixed air are presented in the state table.
Solution: The dry-bulb temperature is approximately 19.6 °C, and the wet-bulb temperature is approximately 14.6 °C.
Psychrometric Process Visualization
Point 0: Initial air state (4.0°C, 70.7% RH)
Point 1: Final air state (19.6°C, 58.0% RH)
Implementation Standards
The psychrometric calculations in this tool follow the standards established by ASHRAE [1], [2]. The calculation library is open source and available on GitHub: https://github.com/kanamesasaki/psychroid. Contributions are welcome! Please open an issue or submit a pull request if you have suggestions for improvements, bug fixes, or additional features.