Thursday, March 1, 2012

End Reflection Hits The Street

The reality of the new end reflection change in discharge sound is starting to get out, so there are lots of questions. I explained the issue a few weeks back in my "End Reflection Blog". The impact is not as great as one might expect, as it only affects low frequencies, but at the same time, smaller units with small outlet ducts where sound levels are typically very low will see a greater difference. This will likely not affect terminal unit selections for most applications. The biggest issue is meeting scheduled sound levels created before the change in reported discharge sound levels.

AHRI has been tasked with releasing a white paper and putting a notice of the change in major trade magazines. That hasn’t happened yet, but it is in progress. In the meantime, most manufacturers have updated their AHRI ratings. Their on-line catalogs are slowly being updated. Most should include a reference to the new standard on the page where data is shown. I expect it will be a while before all on-line catalogs are up-to-date with the new standard. Software updates will likely take a while longer. In addition to the changed data, there are a couple of other changes required, which will likely require everyone to recompile their programs.

For a while at least, there will be two sets of discharge sound data floating around. Everyone needs to be careful which version of the data is being quoted and engineers need to begin modifying their acoustical requirements. We strongly recommend that engineers specify maximum allowed sound power using the AHRI 885 algorithms, starting with desired room sound pressure by octave band, and working backward to calculate the maximum allowed power levels. Krueger has such a spreadsheet, located on the Krueger website at

Authored by: Dan Int-Hout, Chief Engineer Krueger