Duct Design Calculator
| Duct Material | Duct Shape | Length (mm) | Dim 1 (mm) | Dim 2 (mm) | Flow Rate (L/s) | # Fire Dampers | # Volume Dampers | # VAV Units | # Flex. Connectors | # 90° Elbows | # 45° Elbows | # Double 90° Elbows | Duct Loss (m) | Action | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Overall Duct Loss: | 0.000 | ||||||||||||||
🧮 How Our Duct Design Calculator Works
Our Duct Design Calculator is designed to provide HVAC engineers with a quick, reliable, and technically sound method to estimate pressure losses in duct systems. It integrates fundamental fluid mechanics concepts—such as Bernoulli’s equation and the Darcy–Weisbach friction formula—to help you calculate how much energy is lost as air travels through duct networks.
This tool helps assess the impact of duct geometry and fitting types on the overall performance of your HVAC system.
🔍 Key Engineering Principles
✅ Bernoulli’s Equation
This classic equation assumes that the total energy (or “head”) in a moving fluid remains constant along a streamline under ideal conditions. It balances:
- Pressure head
- Velocity head
- Elevation head
This lays the groundwork for understanding how energy is transformed as air flows through the system.
✅ Continuity Equation
Using the relationship:
Q = V × A
(Flow rate = Velocity × Cross-sectional Area)
…the calculator determines average air velocity, which is essential for friction loss calculations and proper duct sizing.
✅ Darcy–Weisbach Equation
Real-world duct systems face friction losses from wall contact. This formula computes losses based on:
- Duct length
- Hydraulic diameter
- Air velocity
- Friction factor
It’s widely accepted in professional HVAC design calculations.
✅ Fitting Losses
Beyond straight duct runs, air encounters turbulence and resistance in:
- Fire dampers
- Volume control dampers
- VAV boxes
- 90°/45° elbows
- Double 90° elbows
- Flexible connectors
Each is assigned a K value (loss coefficient). Default values are prefilled, but you can input custom K values for greater accuracy.
📏 Standards and Best Practices
🔹 ASHRAE Fundamentals
Our calculator is based on methodologies from the ASHRAE Handbook—a globally recognized standard in HVAC design. By combining Bernoulli and Darcy–Weisbach principles, we maintain engineering rigor and credibility.
🔹 Engineering Conventions
- All units follow metric standards.
- Automatic conversions from mm to meters and L/s to m³/s.
- Uses standard air properties at typical indoor conditions (20°C, 101.3 kPa).
🔹 Flexible K-Value Input
Default K values are based on manufacturer norms, but we recognize variability. That’s why we offer a Global Custom Override—just enter your own values if you have verified specs.
🛠️ Using This Calculator
To begin, just:
- Select duct material and shape.
- Enter dimensions and length (in mm).
- Provide flow rate (in L/s).
- Input the number of each fitting.
- (Optional) Add custom K values under “Global Custom K Overrides.”
📊 Sample Results (Based on Default Input)
- Average Velocity (V): 0.833 m/s
- Hydraulic Diameter (Dh): 0.343 m
- Cross-Sectional Area (A): 0.120 m²
- Reynolds Number (Re): 19048
- Friction Factor (f): 0.0272
Duct Friction Loss:
- Pressure Drop: 0.13 Pa
- Head Loss: 0.011 m
Fittings Loss (Total K = 5.00):
- Pressure Drop: 2.10 Pa
- Head Loss: 0.177 m
Total System Loss:
- Pressure Drop: 2.23 Pa
- Total Head Loss: 0.188 m
✅ Conclusion
Whether you’re doing a quick sanity check or a comprehensive duct layout, this calculator helps estimate losses with confidence. It’s flexible, standards-aligned, and customizable—everything an HVAC engineer needs for informed decision-making.
🖨️ Don’t forget: You can print the results using the “Print Output” button for neat, professional documentation.