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
Chapter 3–HVAC Sound Sources
Figure 8. Fan Sound Power Level Correction for Off-Peak Efficiency Operation.
Example Fan Sound Power Level Calculation
Assume an HVAC system design will use a 30-inch diameter backward inclined 10 blade
centrifugal fan to deliver 15,000 cfm at a static pressure of 4.00 in. WC. According to
manufacturer’s data, this requires the fan to rotate at 1,300 rpm.
Determine the actual sound power level to be expected under those conditions assuming the
actual manufacturer’s data is the same as Table 5.
Step 1. Actual Operating Conditions Increase
The second horizontal line of values (up to 36-inch Wheel Diameter) in Table 5 applies to a
30” backward inclined centrifugal fan. Using the FLw formula, calculate the dB level increase
for the eight octave bands.
FLw = 10 Log + 20 Log P
= 10 Log 15,000 + 20 Log 4
= 10 (4.2) + 20 (0.6)
= 42 + 12.0
= 54
Table 8 summarizes Step 1, 2, and 3 sound calculations beginning with the initial dB values
obtained from Table 5, and resulting in the final actual operating conditions dB values.
28 Siemens Building Technologies, Inc.