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56 TRG-TRC013-EN
notes
period four
Application Considerations
the fan outlet, this system effect should be accounted for in the fan selection. If
an elbow, turning vanes, air straightener, or other obstruction is located too
close to the fan inlet, this system effect should also be accounted for in the fan
selection. Additionally, the effects of preswirling the air prior to it entering the
fan wheel, or the use of an inlet plenum or cabinet, must also be considered.
System-effect correction factors are published by the Air Movement and
Control Association (AMCA) and fan manufacturers, to aid in accounting for
these additional losses before the system is installed. These factors are velocity
dependent and are simply added to the estimated static-pressure loss for the
rest of the system.
Finally, factory-supplied accessories such as silencers, flanges, screens, and
guards may also create additional pressure drops that the fan must overcome.
This information is generally published by the manufacturer and should be
accounted for during fan selection.
Acoustics
Proper acoustics are essential for a comfortable environment. The sound at any
particular location is the sum of sounds emanating from many sources. HVAC
equipment, copiers, lights, telephones, computers, and people all contribute to
the noise in the space. The challenge for the HVAC system designer is to
anticipate this and create an environment that allows speaking, sleeping, or any
other activity for which the space was designed.
The air-handling equipment is generally a key noise source that must be
addressed in order to ensure a quiet, comfortable space. Sound from a fan
often follows more than one path to the receiver in the space. In this example, a
fan (located inside an air handler) is installed in a mechanical equipment room
next to an occupied space. The sound from this fan ➀ travels with the supply air
to the space, ➁ breaks out of the supply ductwork over the space, ➂ radiates
from the air handler casing and through the wall, and ➃ travels from the fan
inlet, through the return duct system, to the space. All of these paths must be
controlled to achieve the desired sound level in the space.
Acoustics
radiated
radiated
return
return
airborne
airborne
supply
supply
airborne
airborne
supply
supply
breakout
breakout
1
1
2
2
3
3
4
4
Figure 81