Air Distribution Engineering
Comprehensive technical specifications for optimal duct system design.
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Velocity Parameters
- Main Trunk: 800-1000 FPM
- Branch Ducts: 600-800 FPM
- Residential Supply: 700-900 FPM
- Return Air: 600-700 FPM
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Friction Rate Design
- Optimal Range: 0.08-0.15 iwc/100ft
- Maximum Rate: 0.25 iwc/100ft
- Branch Loss: 0.05-0.08 iwc
- Total Static: 0.5-1.0 iwc
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Sizing Equations
- Area = CFM ÷ Velocity
- Diameter = √(4 × Area ÷ π)
- Aspect Ratio: ≤ 4:1 recommended
- Equivalent Length: L + (1.5 × D)
System Design Parameters
Critical specifications for duct system performance:
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Flow Characteristics
- Reynolds Number: 4000+ turbulent
- Roughness Factor: ε = 0.0003 ft
- Dynamic Losses: Σ(C × Vp)
- Leakage Class: ≤ 6 (sealed)
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Material Properties
- Sheet Metal Gauge: 24-30 GA
- Insulation R-Value: 6-8 min
- Vapor Barrier: 0.02 perm max
- Fire Rating: Class 1/Class A
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Installation Standards
- Hanger Spacing: 8-10 ft max
- Sealing Level: SMACNA Class A
- Support Load: 1.5 × weight
- Deflection Limit: L/240 max
Performance Metrics
Key parameters for system evaluation and testing:
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Testing Standards
- Pressure Test: 2× operating
- Leakage Rate: ≤ 5% design flow
- Balance Tolerance: ±10% design
- Noise Criteria: NC-35 max
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System Efficiency
- Transport Factor: 0.75-0.85
- Fan Power Index: ≤ 0.8 W/cfm
- Distribution Loss: ≤ 15%
- System Effect Factor: ≤ 0.5
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Acoustic Control
- Breakout Loss: 40+ dB
- Insertion Loss: 20-30 dB
- Regenerated Noise: NC-25
- Room Criteria: RC-30 max