Calculator Inputs
Page sections stay in one vertical flow. The input area uses three columns on large screens, two on medium screens, and one on mobile screens.
Example Data Table
| Scenario | Dry-Bulb | RH | Pressure | Humidity Ratio | Dew Point | Wet-Bulb | Enthalpy |
|---|---|---|---|---|---|---|---|
| Office Comfort Point | 24.00 °C | 50.00 % | 101.325 kPa | 9.276 g/kg | 12.94 °C | 17.14 °C | 47.76 kJ/kg |
| Humid Coastal Air | 30.00 °C | 70.00 % | 101.325 kPa | 18.752 g/kg | 23.93 °C | 25.60 °C | 78.13 kJ/kg |
| Dry Supply Air | 14.00 °C | 35.00 % | 101.325 kPa | 3.447 g/kg | -1.23 °C | 6.87 °C | 22.79 kJ/kg |
Formula Used
1) Saturation Vapor Pressure
Pws = 0.61094 × exp[(17.625 × T) / (T + 243.04)]
2) Vapor Pressure
Pv = RH × Pws / 100
3) Humidity Ratio
W = 0.621945 × Pv / (P − Pv)
4) Specific Enthalpy
h = 1.006 × T + W × (2501 + 1.86 × T)
5) Specific Volume
v = 0.287042 × (T + 273.15) × (1 + 1.607858 × W) / P
6) Moist Air Density
ρ = (1 + W) / v
7) Dew Point
Td = 243.04 × ln(Pv / 0.61094) / [17.625 − ln(Pv / 0.61094)]
8) Wet-Bulb Estimate
The calculator uses the Stull approximation for a fast engineering wet-bulb estimate.
These relationships are excellent for HVAC calculations and chart-based engineering estimates. They are simplified over-water formulas rather than full high-precision psychrometric standards.
How to Use This Calculator
Step 1
Choose SI or IP units before entering values.
Step 2
Enter dry-bulb temperature and relative humidity for the air state.
Step 3
Provide barometric pressure. Local pressure improves accuracy for altitude-sensitive projects.
Step 4
Add airflow if you want dry-air mass flow, moisture flow, and enthalpy flow.
Step 5
Set the chart maximum temperature to match the process range you want to visualize.
Step 6
Submit the form. Review the result table, metric cards, and the plotted state point.
Step 7
Use the CSV export for spreadsheets and the PDF export for reports or design documentation.
FAQs
1) What does this calculator solve?
It estimates common humid-air properties from dry-bulb temperature, relative humidity, pressure, and optional airflow. Outputs include humidity ratio, dew point, wet-bulb temperature, enthalpy, density, and a plotted chart point.
2) Is this useful for HVAC work?
Yes. It is well suited for HVAC design checks, air-handling studies, comfort analysis, supply-air review, and quick process-air estimates where a simplified engineering chart is acceptable.
3) Why is pressure included?
Pressure changes humid-air properties because the same moisture content behaves differently at different altitudes. Using local pressure improves humidity ratio, specific volume, and density estimates.
4) What is humidity ratio?
Humidity ratio is the mass of water vapor carried by one unit mass of dry air. It is often expressed as g/kg dry air or grains per pound dry air.
5) Is the wet-bulb result exact?
The wet-bulb value is a fast engineering approximation based on the Stull equation. It is highly practical for design screening, though laboratory-grade work may require a stricter standard method.
6) What does the airflow input do?
Airflow lets the calculator estimate dry-air mass flow, moisture transfer rate, and enthalpy flow. That helps when checking coils, ventilation loads, or process-air delivery.
7) Can I use IP units?
Yes. Select IP to work with °F, psia, and CFM. The calculator converts internally, then presents outputs in engineering-friendly imperial terms.
8) Why does the chart look simplified?
The graph focuses on the most useful curves for quick interpretation: relative humidity lines and the selected state point. It is designed for clarity, not full printed-chart complexity.