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 Components
Although a fan is not designed with the intention of deliberately creating sound, a sound
component, in addition to aerodynamic sound, is nonetheless generated as the result of fan
blade vibration during rotation. This component of fan sound is referred to as the blade
frequency increment (BFI). In some situations this component of the fan sound can be the
major source of annoyance. Therefore, it is a very important part of calculating the sound
power level of a fan in a given application.
Fan Efficiency
Another factor that affects the actual sound power level of a fan is its operating efficiency.
The closer a fan operates to its peak efficiency conditions, the lower the aerodynamic sound
that will be produced.
Fan Sound Power Level Data
To calculate the expected sound power level of a particular fan in a specific application, we
need the fan manufacturer’s certified sound power level data for the size and type of fan
we’re interested in. When selecting a fan for a given set of operating conditions, the ideal
situation is to use the fan manufacturer’s actual certified sound data.
However, since designers typically don’t want to design a system around one specific fan
manufacturer, they can use the sound power level data for typical fans that ASHRAE has
published. Table 5 reproduces this data for your convenience.
Table 5. Typical Sound Power Levels of Various Fans at 1 cfm and 1.00 in. WC.
Fan Type
63H
z
125H
z
250H
z
500H
z
1kH
z
2kH
z
4kH
z
8kH
z
BFI
Centrifugal Airfoil
Over 36-inch
Wheel Diameter
40 40 39 34 30 23 19 17 3
Backward Curved
Backward Inclined
Up to 36-inch
Wheel Diameter
45 45 43 39 34 28 24 19 3
Centrifugal
Forward Curved
All Diameters 53 53 43 36 36 31 26 21 2
4 to 10 in. WC 56 47 43 39 37 32 29 26 8
6 to 15 in. WC 58 54 45 42 38 33 29 26 8
Centrifugal Radial
15 to 60 in. WC 61 58 53 48 46 44 41 38 8
.3 to .4 Hub
Ratio
49 43 43 48 47 45 38 34 6
.4 to .6 Hub
Ratio
49 43 46 43 41 36 30 28 6
Vaneaxial
.6 to .8 Hub
Ratio
53 52 51 51 49 47 43 40 6
Under 40-inch
Wheel Diameter
51 46 47 49 47 46 39 37 7 Tubeaxial
Over 40-inch
Wheel Diameter
48 47 49 53 52 51 43 40 7
Siemens Building Technologies, Inc. 25