period four
Equipment Sound Rating
notes
Ducted Air-Handling Equipment
| supply-air outlet |
coil | return-air |
inlet |
supply fan | outdoor-air |
| intake |
Figure 63
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.