This paper is based on findings resulting from ASHRAE Research Project RP-1219.

Duct rumble noise in HVAC air distribution systems is commonly attributed to the poor aerodynamic discharge conditions of fan outlets. To date, qualitative descriptors published in ASHRAE Handbooks have been used as design guidelines for engineers to limit the amount of duct rumble noise. ASHRAE funded a project, RP-1219, to quantify the rumble noise as the fan discharge orientation and distance from a duct is varied. A test system was built and verified to measure discrete frequency and one-third octave spectra in an adjoining room to the fan room. Tones, associated with vibration, were removed from the spectra, so that the one-third octave band data focused on analysis of the aerodynamic noise. Results for the fan discharge orientation and distance relative to a 90 degree elbow are presented. Some trends are identified; however, overall the results indicate a need for testing with additional fans and coupling the testing with measurements of the fan discharge air flow.

Units: I-P