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
When the Strouhal numbers are calculated for each octave band, use Figure 12 to obtain the
K factors. Before using Figure 12, the velocity ratio M, between main duct airflow velocity
(UM) and branch duct airflow velocity (U
B
) is calculated as:
M = U
M
÷ U
B
The K factors may also be calculated using the following very lengthy formula:
K = -21.6 + 12.4 M
0.67
- 16.5 M
-0.3
(Log St) 5.0 M
-0.25
(Log St)
2
Figure 12. K versus Strouhal Number for Junctions.
JC Factor
JC is a constant that depends upon the configuration of the junction and relates to the
junction’s ability to attenuate sound.
JC = -107 + Δr + ΔT
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