ダクトサイズ基準：ASHRAE vs GB vs SHASE 風速比較
ASHRAE/SMACNA（北米）、中国GB基準、日本SHASE-S 010の推奨ダクト空気風速の並列比較。
概要
Duct sizing is a balance between pressure drop, noise generation, material cost, and space constraints. Higher velocities reduce duct size and material cost but increase noise and fan energy consumption. Three major standards provide velocity guidance for duct design: ASHRAE/SMACNA (North America), China GB standards, and Japan SHASE-S 010. Each reflects regional priorities in noise tolerance, construction practices, and energy costs.
The velocity recommendations differ substantially. ASHRAE/SMACNA allows the highest velocities, reflecting North American practice of centralized air handling with longer duct runs. GB standards prefer conservative velocities for quieter operation. SHASE-S 010 provides differentiated guidance for residential and commercial applications, with particular attention to branch duct noise control.
パラメータ比較
| パラメータ | ASHRAE / SMACNA | GB | SHASE-S 010 |
|---|---|---|---|
| 既定設計風速 | 7.0 m/s | 4.0 m/s | 6.0 m/s |
| 最適風速範囲 | 5 — 10 m/s | 3 — 6 m/s | Office main: 8 m/s, branch: 5 m/s |
| 最大風速 | 12.0 m/s | 8.0 m/s | Res main: 5 m/s, branch: 3 m/s |
| 枝ダクト推奨値 | 3.0 m/s | 2.0 m/s | 3.0 m/s (residential) |
| 住宅主ダクト | 5.0 m/s | 3.5 m/s | 5.0 m/s |
| 業務用主ダクト | 7.0 — 10.0 m/s | 5.0 — 7.0 m/s | 6.0 — 8.0 m/s |
| 高速システム | Up to 12.0 m/s | Up to 8.0 m/s | Up to 10.0 m/s |
| 低騒音/住宅 | 3.0 — 4.0 m/s | 2.0 — 3.5 m/s | 2.0 — 3.0 m/s |
計算式の違い
All three standards use the fundamental duct sizing equation Q = A × V where Q is airflow (m³/s), A is duct cross-sectional area (m²), and V is velocity (m/s). The friction loss is calculated using the Darcy-Weisbach equation or the Colebrook formula for friction factor. However, the standards differ in their recommended friction rate targets: ASHRAE typically uses 0.1 in. w.g./100 ft (0.8 Pa/m), GB uses 0.5 — 1.0 Pa/m, and SHASE-S 010 uses 0.8 — 1.2 Pa/m for main ducts and 0.5 — 0.8 Pa/m for branch ducts.
The velocity-pressure relationship follows ΔP = 0.5 × ρ × V² × (fL/D + ΣC) where f is the friction factor, L is duct length, D is hydraulic diameter, and C represents minor loss coefficients. Higher velocities in ASHRAE designs mean fittings must be carefully selected to avoid excessive pressure drop, whereas GB's conservative velocities allow simpler fitting designs.
設計への影響分析
Velocity choice directly affects three key design outcomes: duct size, fan energy, and noise level. Designing to ASHRAE's 7.0 m/s default produces approximately 40% smaller duct cross-sections than GB's 4.0 m/s default. This translates to significant savings in sheet metal cost and ceiling space — a critical factor in commercial buildings with limited plenum depth.
However, the higher velocity increases duct system pressure drop roughly with the square of velocity. At 7.0 m/s, friction losses are approximately 3 times higher than at 4.0 m/s for the same airflow. This means higher fan static pressure, increased fan energy consumption, and potentially higher sound levels. Sound attenuation may require additional duct silencers, offsetting some of the material savings.
地域別適用性
ASHRAE/SMACNA velocity guidelines are appropriate for North American projects where ductwork is typically fabricated from galvanized steel with spiral or longitudinal seams. The higher velocities reflect the prevalence of VAV systems and central air handling. GB standards are suited for Chinese projects where noise regulations are stricter and duct construction tolerances differ. SHASE-S 010 is widely adopted in Japan and is well-suited for projects requiring differentiated velocity treatment between main and branch ducts, particularly in multi-zone residential and office buildings.
よくある質問
ASHRAE/SMACNAが推奨する既定ダクト風速は？
ASHRAEとSMACNAは典型的な業務用空調システムに対し既定ダクト風速7.0 m/sを推奨。
GB基準がASHRAEより低いダクト風速を規定する理由は？
中国の設計慣行がより低い騒音レベルと圧力損失の低減を優先しているため。
SHASE-S 010の住宅用ダクト風速推奨値は？
SHASE-S 010は住宅用に主ダクト最大5.0 m/s、枝ダクト最大3.0 m/sを推奨。
騒音に敏感な用途に最適な基準は？
GB基準の低い既定風速4.0 m/sが一般的に最適。
異なる基準のパラメータを混合使用できますか？
単一の設計で異なる基準のパラメータを混合することは推奨されません。