Login

Email   Password
       
  
 

Why Join ASHRAE

ASHRAE Membership

ASHRAE membership is open to any person associated with heating, ventilation, air conditioning or refrigeration. ASHRAE is unique because its membership is drawn from a wide range of disciplines relating to the HVAC&R field. Over 56,000 individuals from more than 100 nations belong to the Society.

Discounts on Publications

ASHRAE members earn 15% off publications. Hundreds of titles are available including the complete collection of ASHRAE Standards including 90.1, 62.1 and 189.1.
JOIN ASHRAE

Develop Leadership Skills

When you join ASHRAE, you are making an investment in yourself. When you become active in the Society by giving your time and sharing your knowledge, you get even more out of that investment.

Network with Industry Professionals

Each month, all over the world, ASHRAE chapters convene for an informational program featuring a speaker or topic that is key to professionals in the industry. Meet with your peers and share ideas.
 
 
Need technical info? Search ASHRAE's Bookstore >
 
 
Resources & Publications
 

Article_Paulauskis.jpg

©2016 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 58, no. 12, December 2016

John A. Paulauskis, Member ASHRAE

About the Author
John A. Paulauskis is owner of JPAcoustics in Maryville, Illinois.

To determine a common source of duct rumble, 22 HVAC duct system case histories for various clients between 1984 and 2014 were studied. The case histories included actual field measurements and duct rumble remediation controls. Trial-and-error duct rumble reduction led to specific design and retrofit techniques to reduce duct rumble. The term “duct rumble” is incorrectly defined in the HVAC industry as low-frequency fan noise that “breaks out” of ductwork.

The cases summarized in this article exclude fan noise breakout, and conclude that duct rumble is a physical phenomenon that occurs as a combination of airflow turbulence caused by duct fittings with poor aerodynamics, pressure pulsation in the ductwork at the fan speed frequency, and the resulting vibration of the ductwork at resonance. In fact, duct rumble is often described by building occupants as “vibration” instead of “sound,” and can also cause a feeling of pressure and vibration on the ears, head, and chest, and will cause secondary vibration of things like cups, indoor drywall partitions, and bric-a-brac.

The conclusions reached for the sources of duct rumble were a result of reviewing the case history sound and vibration data, and by the trends of increased duct rumble and duct vibration levels during an empirical study. The conclusions can provide the basis for further research to understand duct rumble.

 

Background

Duct rumble characteristically has low-frequency “sound” energy between 20 Hz and 63 Hz, but can also have energy below 20 Hz. Case history complaints of duct rumble were generated when the low-frequency rumble was less than or equal to 63 Hz and 70 dB sound pressure level in the occupied spaces. “Sound,” by definition, is a sensation experienced when the brain interprets vibrations within the structure of the ear caused by rapid variations in the air pressure above and below normal atmospheric pressure.

If the air pressure changes have major frequency components below 20 Hz, which is below our normal hearing range, it is called “infrasound.” With infrasound, our bodies respond differently than we do for audible sound. Our body parts, such as our abdomen, arms, legs, and shoulders, sense infrasound through our tactile senses, not through our ears. Air perturbations in the infrasound frequency range can cause us to be anxious, nauseous and affect our sleep habits. One source of infrasound that has recently been studied for its adverse effects on humans is the infrasound from large wind turbine axial fans. Similar adverse human reactions have been observed for many of the cases.

 

Case Histories

The 22 cases covered a wide range of fan types and ductwork conditions in schools, hospitals, offices, banks, and hotels. The cases involved rooftop units (RTUs); in-line, vane-axial type return/relief air fans; and centrifugal fans. Cases included both direct and belt-drive fans, and one recent case involved a fan-wall duct system with direct-drive supply air fans.

In two cases, the duct rumble also occurred more than 80 ft (24 m) upstream of the return air fans where a series of duct elbows and fire/smoke dampers combined to generate high static pressure drops across the fittings. Several case histories also demonstrated how the vibrating ductwork inside a mechanical room can cause a nearby drywall partition and objects such as metal cabinets to resonate, although the drywall partition was not connected physically to the ductwork.

 

Read the Full Article

 

Return to Featured Article Excerpts

 

Comments

    Leave a Comment


    Name*
    Email*

    (For verification purposes only.)

    Comment*

    Enter the text shown in this image:*(Input is case sensitive)


    * - Only comments approved by post editor will be displayed here.