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
Elbow Airflow Noise
Where:
ELw = the net elbow sound power level increase (or decrease if it is negative).
K = a factor that is dependent upon the elbow operating conditions.
F = the octave band center frequency in Hz.
U = the duct airflow velocity.
S = the duct cross sectional area in square feet.
D = the height of the elbow in feet for elbows without turning vanes.
D = the cord length of a vane in feet for elbows with turning vanes.
EC = a constant that depends upon the type of elbow and relates to the elbow’s ability to
attenuate sound.
For an elbow without turning vanes, EC = -107.
For an elbow with turning vanes, EC = 10 Log n -107, where n is the number of turning
vanes.
K Factor
The K factor is determined by first calculating the Strouhal number. Since the Strouhal
number is dependent upon the octave band frequency, a separate Strouhal number (St) and
K factor must be determined for each of the eight octave bands.
Strouhal number (St) = 60 F D ÷ U
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