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The research project documented here, ASHRAE RP-1314, explored a number of issues pertaining to End Reflection Loss (ERL). A major focus of the work was to experimentally determine the ERL of a variety of rectangular duct configurations down to low frequency. Further, this work considered the impact that termination variations have on ERL and how experimental results correspond with analytic predictions and current ERL values in the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Handbook. This document represents a distillation of the findings and recommendations of the research project; the complete documentation of may be found in the Masters’ Thesis of Alexander Michaud, “Experimental Investigation of Reflection of Airborne Noise at Duct Terminations,” The Georgia Institute of Technology, 2007. This thesis in its entirety is included in this report as an appendix. Detail on such matters analytical representations, methods, apparatus, configurations, etc. and references may be found in the thesis, and as such, are omitted from the body of this report.

In the body of this report, the research results are presented in turn to speak to each of the following ten issues:

  1. Analytic ERL for Rectangular vs. Circular Ducts
  2. Bandwidth and Spectrum Shape influence on ERL
  3. ASHRAE Table Values vs. Analytic ERL
  4. Flush-terminated Experimental ERL vs. Table and Analytic
  5. Validity of Free-space Duct Termination Condition
  6. Impact of High Aspect Ratio Ducts
  7. Impact of Baffle Hardness
  8. Impact of Flex Duct
  9. Impact of Diffusers
  10. Impact of Return Grills Following discussion of the issues above, this report then presents recommended simplified ERL prediction equations, as well as a discussion of recommendations pertaining to modification of the Handbook.

Units: I-P