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58 TRG-TRC007-EN
notes
period four
Equipment Sound Rating
One of the best examples to demonstrate the complexity of gathering complete
and accurate sound data is air-handling equipment. This involves any type of
HVAC equipment that contains a fan and is used to condition and move air
through a duct system.
Consider that each fan in an air-handling product line may run at multiple
speeds and within a range of flow and static-pressure conditions. The fact
that each type of fan (forward-curved, backward-inclined, and so forth) has a
different operating characteristic further complicates testing.
A fan performs differently inside an air handler than it does in a stand-alone
application. The air-handler casing generally changes the airflow patterns at
the fan inlet and discharge openings, which can change the sound power for
a given flow and static-pressure condition.
Additionally, an air handler may have only one source of sound or it may have
several. For example, a ducted, packaged rooftop air conditioner has multiple
sources. It contains a supply fan, refrigeration compressors, air-cooled
condenser fans, and possibly an exhaust or return fan.
Finally, sound may leave the air handler in multiple ways. In the case of the
indoor air handler, sound travels along with the conditioned air into the supply
duct system. It also travels back out the return-air inlet, against the direction of
airflow. Finally, sound is also radiated by the casing of the air handler into the
equipment room. In order to properly design the HVAC system, the designer
needs to know the sound power from all of these paths.
Ducted Air-Handling Equipment
coilcoil
coil
supply fansupply fan
supply fan
outdoor-air
intake
outdoor
outdoor
-
-
air
air
intake
intake
return-air
inlet
return
return
-
-
air
air
inlet
inlet
supply-air outletsupply
supply
-
-
air outlet
air outlet
Figure 63