Basic Documentation
Table Of Contents
- About this Application Guide
- Chapter 1–Introduction
- Chapter 2–Physics of Sound
- Chapter 3–HVAC Sound Sources
- Chapter 4–HVAC Sound Attenuation
- Introduction to HVAC Sound Attenuation
- Plenums
- Duct Attenuation
- Duct Takeoffs and Divisions
- Duct Silencers
- End Reflection
- Environment Adjustment Factor
- Space Effect
- Radiated Sound Attenuation
- Chapter 5–HVAC System Sound Analysis
- Chapter 6–Minimizing HVAC Sound
- Appendix
- Glossary
- Index
Junction and Takeoff Airflow Noise
Figure 13. Final Corrected Δr Factors for Duct Junctions and Takeoffs with a Radius.
Determine the values for the terms in the Junction Sound Power Level DLw) formula:
JLw = K + 10 Log F + 50 Log U
B
+ 10 Log S+ 10 Log D – JC
Where:
F = the octave band center frequency in Hz: (63, 125, 250, 500, 1,000, etc.).
U
B
= the branch duct air velocity: (1,600 cfm / 1 sq ft = 1,600 fpm).
S = the branch duct area: (1 sq ft).
D = the branch duct height: (1 ft).
Determining the K Factor requires first calculating M and then solving for the Strouhal
number at each octave band center frequency. Then the graph in Figure 12 is used to
determine K.
M = U
M
÷ U
B
U
M
= 14,500 cfm ÷ 6 sq ft
= 2,420 fpm
U
B
= 1,600 fpm
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