ARI 885-98 Update

ARI Standard 885 is the “Standard for Estimating Occupied Space Sound Levels in the Applications of Air Terminals and Air Outlets”. The standard was developed by the Air-Conditioning and Refrigeration Institute (ARI) to establish a uniform industry procedure for estimating sound pressure levels in occupied spaces served by air terminals and/or air outlets. ARI 885 establishes consistent, industry-accepted practices for calculating room sound pressures used to determine the Noise Criteria (NC) of a terminal in a space.

ARI 885-98, as amended by the 2002 Addendum, includes Appendix E which specifies the sound attenuation values for diffuser sound, air terminal discharge sound, and air terminal radiated sound. As of April 2003, all manufacturers are required to publish NC ratings based on ARI 885-98.

Specifically, the standard requires manufacturers to use a 10dB room absorption deduction for diffusers, Type 2 mineral fiber ceiling deducts for terminal radiated sound, and one of three sets of deducts based on CFM for terminal discharge sound.

Many in the industry believed the previous standard, ARI 885-90, was too generous in its attenuation allowances for terminals. ARI reviewed the standard and introduced more accurate attenuation factors in 885-98. The updated allowances are reduced from the previous standard, which will effectively increase the NC rating of any given terminal when compared to the NC rating using the previous standard, ARI 885-90.

The primary changes ARI 885-98 are as follows:

ASHRAE research determined that noise sources above a suspended ceiling should be classified as an area source, not a point source as it was in ARI 885-90. ARI developed a new table used for radiated sound based on a fixed room volume and receiver distance. This new table for Ceiling/Space Effect, based on ceiling type, has decreased attenuation factors than the combined Ceiling and Space Effect tables of 885-90.

The Environmental Adjustment Factor was decreased in ARI 885-98. The table below shows the current and previous Environmental Adjustment Factor.

Octave Band	2	3	4	5	6	7
ARI 885-90 Environmental Adj.	3	2	1	1	1	1
ARI 885-98 Environmental Adj.	2	1	0	0	0	0

The calculation for determining end reflection loss changed in ARI 885-98. The sudden area change at the exit of an integral terminal unit or outlet can reflect significant low frequency energy back into the attached ductwork. This is end reflection loss. The calculation change resulted in a reduction in the attenuation credit for end reflection.

The following table shows the ARI 885-98 attenuation allowance compared to ARI 885-90 allowance:

	Octave Bands
	2	3	4	5	6	7
Radiated Sound Allowance Change	-1	-2	-4	-1	+2	+6
Discharge Sound Allowance Change	-5	-5	-2	-4	-3	-3

The average change between the two standards represents a 4 to 6 NC increase in application data. The following tables show the difference between ARI 885-90 and ARI 885-98 for the same sound power data.

Radiated Sound Attenuation	Octave Bands						NC
Radiated Sound Attenuation	2	3	4	5	6	7	NC
Unit Catalog Sound Power	69	64	60	55	48	42
ARI 885-90 Room Sound Pressure	48	42	36	28	19	12	32
ARI 885-98 Room Sound Pressure	49	44	40	29	17	6	35

Discharge Sound Attenuation	Octave Bands						NC
Discharge Sound Attenuation	2	3	4	5	6	7	NC
Unit Catalog Sound Power	73	69	65	62	62	61
ARI 885-90 Room Sound Pressure	43	38	26	9	9	22	26
ARI 885-98 Room Sound Pressure	48	43	28	13	12	25	33

For equal sound power data, NC ratings cataloged to ARI 885-98 will be higher than previous cataloged data, but will reflect a more realistic sound performance in the field. However, Titus recently introduced an improved flow sensor, the AeroCrossTM, which has significantly reduced the terminals ambient noise generation. The net result of reporting to the new standard and the changeover to the AeroCrossTM is that some NC ratings have increased, while some ratings have decreased compared to past catalogs.