Noise Expert (acoustical engineers) was asked to evaluate the mechanical noise from a rooftop HVAC system located directly above an open office space in Chandler, Arizona.
The low frequency noise levels were very high in the office spaces below the roof top unit. The ductwork takes an abrupt 90 degree turn under the roof in duct that is too small for the volume of air being moved. Hence, the air velocities are very high and cause low frequency rumble.
The proposed to create a storage space below the unit. We specified the construction of the room walls, door seals, and ceiling treatment. They could not extend the walls to the structure so fiberglass batt insulation was placed over the acoustic ceiling tiles.
There is not enough space in the ceiling to enlarge the ducts off of the rooftop unit. Even with the unoccupied storage space below the unit the noise breakout of the ducts outside of the room and the noise through the duct grills was predicted to cause noise levels above the ASHRAE recommended levels. We recommended that they install a duct silencer at the wall of the storage room wall.
Please let us know if you have any questions or if you would like our assistance with acoustical evaluations. 480-332-9325, firstname.lastname@example.org, Noise Expert (acoustical consultants) – www.noiseexpert.com