💨 Duct Sizing & Static Regain

Size circular and rectangular air ducts using Equal Friction and Velocity methods, with Colebrook-White friction, aspect ratio checks, and equivalent diameters.

⚡ Fortran 90 Engine Double Precision (IEEE 754) ✓ ISO / ASME Validated

Hvac

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👁️ Views 19

⚡ Solves 17

💾 Downloads 489 📦 Fortran Code 4.4 KB

📅 Released Jun 2026

⏱️ Latency < 1 ms

💨 HVAC Air Duct Flow Profile & Velocity Boundary Layer

Real-time visual simulation of rectangular & circular duct velocity streamlines

📝 Configuration & Presets

🏢 Office Trunk (8000 m³/h) 🛏️ Hotel Quiet (3.5 m/s) 🍳 Kitchen Hood (9 m/s) 🏥 Cleanroom (14k m³/h)

⚙️ Sizing Method & Cross-Section Shape

Sizing Criteria Method:

Duct Geometry Shape:

💨 Air Flow & Target Constraints

Air Volume Flow Rate Q [m³/h]: 1 CFM ≈ 1.699 m³/h

Target Friction Loss ΔP/L [Pa/m]: Standard: 0.8 to 1.2 Pa/m (0.1 in.wg/100ft)

Target / Max Air Velocity [m/s]: Branches: 3–5 m/s, Mains: 6–8 m/s

Fixed Rectangular Width a [mm]: If rectangular: solves height b

ASHRAE Duct Formulations:
• Equivalent Diameter: D_e = 1.30 · (a · b)^0.625 / (a + b)^0.25
• Friction Rate: ΔP/L = f · (ρ v²) / (2 D_e)
• Velocity Pressure: P_v = ½ ρ v² [Pa]
• Aspect Ratio: AR = max(a, b) / min(a, b) ≤ 4:1

📊 Sizing Results & Dimensions

📊 Output Summary
💾 Fortran Source

Recommended Commercial Duct Dimensions

Ø 256 mm (DN250)

Equivalent Round Diameter: Ø 256.3 mm (AR = 1.00:1)

3.50 m/s

Actual Friction Loss Rate (ΔP/L) 0.62 Pa/m 0.008 in.wg/100ft

Velocity Pressure (P_v) 7.4 Pa Dynamic Head

Acoustic Velocity Classification 3.50 m/s ✅ Low Acoustic Noise (Offices / Bedrooms NC ≤ 30)

Volumetric Airflow in CFM 383 CFM 650 m³/h

📈 Equivalent Round Diameter vs Airflow Rate Q

📉 Friction Loss Rate (Pa/m) vs Air Velocity

=================================================================
 THERMOFLUIDCALC — ASHRAE / SMACNA DUCT SIZING REPORT
=================================================================
Case Title                 : Hotel Guest Room Acoustic Low-Noise Branch Duct
Air Volume Flow Rate (Q)   : 650.0 m3/h (383 CFM)
Target Sizing Method       : Velocity Method
-----------------------------------------------------------------
Equivalent Round Diameter  : 256.29 mm (Ø 10.1 in)
Air Velocity in Duct       : 3.50 m/s (689 FPM)
Velocity Dynamic Pressure  : 7.37 Pa
Friction Loss Rate (dP/L)  : 0.617 Pa/m (0.0075 in.wg/100ft)
=================================================================

📘 Calculation Methodology & ASHRAE Standards

Equal Friction & Huebscher Equivalence

The Equal Friction method maintains uniform pressure drop per unit length. The Huebscher formula computes rectangular ducts with equivalent flow capacity:

                    De = 1.30 · (a · b)0.625 / (a + b)0.25
                

Aspect Ratio & Noise Criteria

Rectangular ducts should maintain aspect ratio $AR \le 4:1$ to minimize sheet metal weight and prevent acoustic rumble generated by high velocity gradients.

Key Engineering Assumptions

Standard air density $\rho = 1.204\,\text{kg/m}^3$ at $20^\circ\text{C}$ and $101.325\,\text{kPa}$.
Galvanized steel absolute roughness $\epsilon = 0.09\,\text{mm}$.
Standard commercial 25 mm dimensional increments applied for fabrication.

ThermoFluidCalc Engineering Report