Online Psychrometric and Duct Calculator — Temperature, Humidity & Duct Losses

Professional Psychrometric and Duct Calculator for System Design and Troubleshooting

What it is

A professional psychrometric and duct calculator is a tool that combines psychrometric calculations (air properties and moisture relationships) with duct sizing and airflow/pressure loss computations to support HVAC system design, performance analysis, and troubleshooting.

Key functions

• Psychrometrics: dry-bulb/wet-bulb temperatures, relative humidity, dew point, enthalpy, specific humidity, humidity ratio, and saturated properties.
• State plotting: locate air states on a psychrometric chart and show processes (heating, cooling, humidification, dehumidification, mixing).
• Duct sizing: compute required duct dimensions for target airflow (CFM), using velocity or friction methods.
• Pressure/flow losses: estimate pressure drop from straight runs, fittings (elbows, transitions, takeoffs), grilles/registers, and filters.
• Fan selection & system curve: calculate system static requirements and match to fan performance curves.
• Heat load impacts: integrate coil load changes with supply/return conditions to size coils and verify capacities.
• Unit conversions & standards: support SI/Imperial units and common HVAC standards (e.g., ASHRAE conventions).

Typical inputs

• Indoor/outdoor dry-bulb and wet-bulb temperatures (or relative humidity).
• Desired supply/return temperatures, airflow (CFM or m3/s).
• Duct material, roughness, length, number/type of fittings.
• Filter type and face velocity, grille/ diffuser loss coefficients.
• Fan efficiency and available motor data.

Typical outputs

• Air property table: enthalpy, humidity ratio, dew point, specific volume.
• Psychrometric process visualization (state changes and energy transfers).
• Recommended duct sizes (rectangular/round) for specified velocities or friction rates.
• Pressure drop per segment and total system static pressure.
• Fan selection guidance: required static pressure vs. flow point.
• Coil loads and supply/return energy balances.

Use cases in design & troubleshooting

1. Sizing new systems: determine duct dimensions and fan requirements for target CFM and acceptable velocities.
2. Retrofit analysis: evaluate how changes (filters, added fittings, reduced duct area) affect pressure drop and fan performance.
3. Humidity control: size dehumidification or humidification equipment and predict condensation risk.
4. Commissioning & diagnostics: compare measured temperatures/pressures to calculated expectations to find leaks, blockages, or fan issues.
5. Energy optimization: identify high-pressure-loss sections and opportunities to reduce fan energy via duct redesign or reduced velocities.

Accuracy considerations & limitations

• Precision depends on input accuracy (measured temperatures, true duct roughness, actual fitting losses).
• Fitting loss coefficients vary by installation; default values are estimates.
• System curves and fan performance require manufacturer data for final selection.
• Transient or stratified conditions require more advanced modeling than steady-state calculators provide.

Quick workflow (recommended)

1. Enter indoor/outdoor conditions and target supply CFM.
2. Compute psychrometric properties and required coil loads.
3. Define duct layout, lengths, materials, and fittings.
4. Calculate section-by-section pressure drops and total system static.
5. Select ducts to meet velocity/friction standards and choose a fan matching the system curve.
6. Verify results against manufacturer data and field measurements; iterate as needed.