Sunday, January 24, 2016: 9:45 AM-10:45 AM
Systems and Equipment
Chair:
Thomas H. Kuehn, PhD, University of Minnesota
Ducts transmit much of the noise heard in office environments. This session uses finite element simulation to determine the attenuation that can be expected from insertion losses, transmission losses, elbows, side branches and breakout transmission loss in lined and unlined ducts for a much wider range of conditions than those provided in the Handbook tables. The results have demonstrated good agreement with available measured data.
1 A Simulation Approach to Determine the Insertion and Transmission Loss of Unlined and Lined Ducts (RP-1529) (OR-16-001)
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David W. Herrin, Ph.D., P.E., University of Kentucky |
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Kangping Ruan, Ph.D., University of Kentucky |
One of the primary noise transmission paths in buildings is from HVAC equipment through ventilation ducts. The ASHRAE Handbook provides tables for estimating the attenuation of lined and unlined ducts up to 10 ft (3.05 m) in length. The aim of this research is to suggest and validate a finite element approach to determine the attenuation of ducts of any length and dimension. The approach detailed simulates the standard measurement approaches for assessing duct attenuation. The duct air space, including the source and termination, is modeled using acoustic finite elements. Poroelastic finite elements are used to simulate the fiber lining, and the metal ductwork is modeled using structural finite elements. The model is used to determine the insertion and transmission loss of unlined and lined ducts. Predicted results are compared to measurement with good agreement.
2 Simulation of Attenuation due to Elbows and Side Branches and Breakout Transmission Loss (RP-1529) (OR-16-002)
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David W. Herrin, Ph.D., P.E., University of Kentucky |
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Kangping Ruan, Ph.D., University of Kentucky |
The primary path of noise propagation in buildings is airborne transmission from building equipment through ducts. Attenuation is increased if elbows or side branches are introduced into a duct. In a companion paper, finite element analysis was used to predict the insertion loss of straight lined and unlined ducts and results were validated with measurement. In this work, finite element analysis is used to predict the attenuation of elbows and side branches. Results for elbows and branches are compared to the ASHRAE Handbook with good agreement. In addition, an important secondary noise transmission path is through duct walls into rooms. This path, which is often termed breakout noise, is also investigated using the finite element approach and results are correlated with an analytical solution and the ASHRAE Handbook with good agreement. Of note, it is demonstrated that the breakout transmission loss is much less than the insertion loss through lined rectangular ducts at some frequencies. This suggests that breakout noise may be the dominant noise path at some frequencies.