End Reflection Calculation and the New Titus Catalog

My new Titus Catalog

The new 2014-2015 Titus catalogs started shipping last week! It's a whole new look and has quite a few new products, but the biggest change may be in the terminal units discharge sound data.

On January 1, 2012, AHRI 880 started requiring that discharge sound power data for terminal units from all manufacturers be adjusted to include end reflection. Everyone in the industry has updated their catalog data when they printed their new catalog. This change is reflected in the new 2014-2015 Titus catalog.

End reflection is sound that is reflected back to the source from the discharge duct termination in the sound chamber. This sound cannot be measured, it can only be calculated. According to ASHRAE research, the end reflection loss can be calculated based on the dimensions of the discharge duct. This calculated end reflection loss (not to exceed 14 dB) must then be added to 1/3 octave band sound data in order to make the correction.

This change was made to correct the fact that room noise criteria (NC) ratings based on AHRI 885 include an end reflection deduction, when in fact the end reflection losses were never included. The end result is that catalog discharge sound levels (both sound power and NC) on all ducted terminal units increased even though the products have remained unchanged. The changes are most noticeable on units with smaller discharge ducts.

So as you look at terminal unit discharge data, be aware that the change in AHRI 880 has changed the sound numbers. If you are comparing catalog sound data from two different manufacturers, it is especially important that you make sure both catalogs have made the update (or both have not) so that you are not comparing one unit's pre-update data to another's post-update data.