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
Fan Sound Power Level Calculation
When the frequency is determined, refer to Table 6 to determine the octave band to which
this frequency applies. The BFI dB value from the manufacturer (or from Table 5) is then
added to the dB obtained in Step 1 for this particular octave band.
Table 6. Octave Band Frequency Division.
(Octave band is listed above the applicable frequency range)
Step 3. Efficiency Correction
Make an appropriate efficiency correction to the sound power level of each octave band
when actual fan operation is intended to be less than 90% of peak efficiency. Table 7 gives
the decibels that must be added to each octave for various efficiency ranges.
When the actual operational efficiency is an unknown (as is typically the situation in the
design stage), determine where the fan will be operating on its fan curve. Figure 8 shows a
typical centrifugal and axial fan curve and the required dB correction for various operational
regions.
Table 7. Efficiency Correction.
% of Peak Static
Efficiency
Add to all
Octaves
90 to 100 0
85 to 89 3 dB
75 to 84 6 dB
65 to 74 9 dB
55 to 64 12 dB
50 to 54 15 dB
For details, see Example Fan Sound Power Level Calculation in this section.
Siemens Building Technologies, Inc. 27