TOOL GUIDE
Psychrometric chart
Determine moist-air properties, compare A/B states, heat-transfer rate and dry-air-based mixing.
Purpose & scope
Determine moist-air properties, compare A/B states, heat-transfer rate and dry-air-based mixing.
Dry bulb −20…60 °C, pressure 60…110 kPa. Supersaturated mixture condensation/fog separation is not modelled; below 0 °C equilibrium is over ice.
Inputs
Use drawings, design conditions and manufacturer data. Units and example values follow the calculator; example values are not universal design requirements.
| Parameter | Value / interpretation |
|---|---|
| Atmospheric pressure · kPa | Local absolute atmospheric pressure for air properties. |
| Input property pair · kPa | Select the second property paired with dry bulb; the next field’s units follow that choice. |
| Dry-bulb temperature · °C | Dry-bulb temperature of the selected state A or B. |
| Relative humidity · % | Second property value: RH %, wet/dew point °C, humidity ratio g/kgda or enthalpy kJ/kgda. |
| Dry-air mass flow · kg/s | Dry-air mass flow for A → B, in kg/s. |
| Stream A fraction in mixture · % | Dry-air mass fraction of stream A in the A+B mixture, in %. |
Steps
- Enter atmospheric pressure and select the input property pair for A.
- Switch to B, enter its properties and enable the desired RH, enthalpy, wet-bulb or specific-volume lines.
- Enter dry-air mass flow and stream A fraction; inspect process results, mixture M and the report.
Worked example
This reproducible training example uses the values below. Select the appropriate mode and overwrite restored project values. Example rates, K values and equipment losses are assumptions, not mandatory design criteria.
Examples use a decimal point and no thousands separator.
All example inputs
| Parameter | Value / interpretation |
|---|---|
| A | 26 °C / 50% RH |
| B | 35 °C / 65% RH |
| Atmospheric pressure | 101.325 kPa |
| Mass flow | 1 kg/s dry air |
| A fraction | 50% A |
Expected results (rounded)
| Parameter | Value / interpretation |
|---|---|
| Humidity ratio A | 10.5 g/kgda |
| Enthalpy A | 52.91 kJ/kgda |
| Heat transfer rate A → B | 42.07 kW |
| Mixture M temperature | 30.55 °C |
Small differences in displayed rounding are normal. A result that passes the entered limits does not establish suitability for the complete system.
Method & limitations
Dry bulb −20…60 °C, pressure 60…110 kPa. Supersaturated mixture condensation/fog separation is not modelled; below 0 °C equilibrium is over ice.
The horizontal axis is dry-bulb temperature; the vertical axis is humidity ratio per kg of dry air. The boundary curve is 100% RH saturation. Toggle relative humidity, enthalpy, wet-bulb and specific-volume lines. Chart temperature range: −20 to 60 °C; the humidity axis expands to include valid points.
Saturation vapor pressure follows Hyland–Wexler/ASHRAE. W = 0.621945·Pv/(P−Pv); h = 1.006·T + W(2501 + 1.86·T). Wet bulb and dew point are solved iteratively. Below 0 °C, saturation and dew point use equilibrium over ice (frost point).
Total heat A → B = ṁda(hB−hA); water added/removed = ṁda(WB−WA). Mixing balances enthalpy and water vapor using dry-air mass fractions. Supersaturated mixtures are flagged; condensation or fog separation is not modeled. RH = 0 has no finite dew point.
ASHRAE — PsychrometricsCommon mistakes
Confusing g/kgda humidity ratio with RH%; entering volumetric flow as kg/s; treating A–B as a simulated coil process; misreading heat-transfer sign.
Projects & reports
- Choose or create an engineering project and enter your actual design inputs.
- Project inputs/results are autosaved in this browser. Where a saved-list panel is available, name and add the selected section or alternative to compare multiple options.
- Review the report before exporting PDF. In the print dialog select Save as PDF. Export JSON for backup and use Open file to restore it; PDF cannot restore project data.
Saved results do not automatically recalculate when another tool changes. Review any dependency warning, recalculate and update the affected results.
References & related tools
The tool implements the methods and limits stated above; linking a standard does not establish complete compliance with that standard.