2001

STANDARD for

AIR DIFFUSERS
AND AIR
DIFFUSER
ASSEMBLIES

FORMALISED BY ISHRAE IN 2008

Standard 890

4301 NORTH FAIRFAX DRIVE z ARLINGTON, VIRGINIA 22203

 IMPORTANT

SAFETY RECOMMENDATIONS
It is strongly recommended that the product be designed, constructed, assembled and installed in accordance with
nationally recognized safety requirements appropriate for products covered by this standard.

ARI, as a manufacturers' trade association, uses its best efforts to develop standards employing state-of-the-art and
accepted industry practices. However, ARI does not certify or guarantee safety of any products, components or
systems designed, tested, rated, installed or operated in accordance with these standards or that any tests conducted
under its standards will be non-hazardous or free from risk.

Note:

This standard supersedes ARI Standard 890-94.

Price $10.00 (M) $20.00 (NM) ©Copyright 2001, by Air-Conditioning and Refrigeration Institute
Printed in U.S.A. Registered United States Patent and Trademark Office
 TABLE OF CONTENTS

SECTION PAGE

Section 1. Purpose ............................................................................................................1

Section 2. Scope ...............................................................................................................1

Section 3. Definitions .......................................................................................................1

Section 4. Classifications..................................................................................................3

Section 5. Test Requirements ...........................................................................................3

Section 6. Rating Requirements .......................................................................................3

Section 7. Minimum Data Requirements for Published Ratings......................................4

Section 8. Marking and Nameplate Data..........................................................................4

Section 9. Conformance Conditions.................................................................................4

FIGURES

Figure 1. Air Stream Patterns..........................................................................................1

APPENDICES

Appendix A. References - Normative...................................................................................5

Appendix B. References - Informative .................................................................................5

Recommendations of Core Committee ......................................................................................5

 ARI STANDARD 890-2001

AIR DIFFUSERS AND AIR DIFFUSER ASSEMBLIES

Section 1. Purpose and designed to distribute air in varying directions
and planes.
1.1 Purpose. The purpose of this standard is to establish
for Air Diffusers and Air Diffuser Assemblies used in air 3.2.2 Diffuser Assembly. A terminal assembly
distribution systems: definitions; classifications; test consisting of a specifically recommended or
requirements; rating requirements minimum data fabricated duct, box, or plenum with an integral or
requirements for Published Ratings; marking and nameplate attached air outlet or diffuser, such as a slot-plenum,
data; and conformance conditions. or slot-duct assembly.

1.1.1 Intent. This standard is intended for the 3.2.3 Grille. A louvered or perforated face over
guidance of the industry, including manufacturers, an opening which is generally located in the sidewall,
engineers, installers, contractors and users. sill, or floor.

1.1.2 Review and Amendment. This standard is 3.2.4 Register. A combination Grille and damper
subject to review and amendment as technology assembly.
advances.
3.2.5 Slot Diffuser or Slot. A long narrow air
outlet (aspect ratio generally greater than 10:1).
Section 2. Scope
3.3 Air Stream Patterns. These are characterized by the
2.1 Scope. This standard applies to Diffusers and following terms (see Figure 1):
Diffuser Assemblies used in air distribution systems which
are duct connected to a remote forced air source, as defined
in Section 3. DIFFUSER

2.2 Exclusions. This standard does not apply to Grilles, TERMINAL

Registers, and troffer diffusers. Sound and pressure VELOCITY
THROW
performance of Diffuser Assemblies providing for automatic ENVELOPE
volume control shall be rated in accordance with ARI
Standard 880.

Section 3. Definitions ANGLE OF DISCHARGE

CENTERLINE OF
All terms in this document shall follow the standard industry PRINCIPAL JET
definitions in the current edition of ASHRAE Terminology of
Heating, Ventilation, Air Conditioning and Refrigeration
SPREAD
unless otherwise defined in this section.

3.1 Air Inlet. A device through which air is removed or Plan View
returned from a conditioned space. (Grilles, Registers,
Diffusers, and Slots may be used as Air Inlets.)

3.2 Air Outlet. A device or opening through which air is

discharged into a conditioned space. It is intended for the
DROP
purpose of this standard that all accessories, connecting duct
SPREAD
adapters, or other mounting airways may be considered part
of the outlet device being tested and shall be, in such cases, THROW
reported as a unit or assembly. Some specific outlet
designations are defined below.
Vertical Cross Section of the Principal Jet
3.2.1 Diffuser. An Air Outlet comprised of
deflecting members generally located in the ceiling Figure 1. Air Stream Patterns

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ARI STANDARD 890-2001

3.3.1 Angle of Discharge. The largest included where An is the nominal area, ft2 [m2], of the duct connection
angle between centerlines of principal jets of the to the Diffuser or Diffuser Assembly.
primary air stream.
3.10 Octave Band. A frequency band of sound covering a
3.3.2 Drop. The vertical distance that the lower range of frequencies such that the highest frequency is twice
edge of a horizontally projected air stream drops the lowest. The Octave Bands used in this standard are
between the outlet and the end of its throw. defined in ANSI Standard S1.11.

3.3.3 Envelope (ISOVEL). The boundary surface 3.11 Pressure. The force per unit area, in H2O [kPa],
of points of equal velocity which describe the air exerted by a homogeneous liquid or gas.
distribution profile (see Figure 1).
3.11.1 Static Pressure (SP). The pressure that
3.3.4 Spread. The maximum distance, in ft [m], would be exerted by a moving fluid on a body
measured parallel to the plane of the outlet between immersed in it if the body were carried along with the
the extremes of the Terminal Velocity Envelope (see fluid. Practically, it is the normal force per unit area
Figure 1). at a small hole in a wall of the duct through which the
fluid flows.
3.3.5 Terminal Velocity (Vt). The highest
sustained velocity in the air stream from an outlet, 3.11.2 Total Pressure (TP). The sum of the
fpm [m/s], which is arbitrarily specified and used to Static and Velocity Pressures, in H2O [kPa].
determine throw (T).
3.11.3 Velocity Pressure (VP). The pressure in a
3.3.6 Throw (T). The distance, ft [m], from the moving fluid, in H2O [kPa], capable of accelerating
center of the outlet to a point in the air stream where the same fluid from rest to the velocity of the fluid
the highest sustained velocity of the air stream has with complete conversion of pressure into kinetic
been reduced to a specified Terminal Velocity (see energy. In this standard, Velocity Pressure is a
Figure 1). Pressure calculated from duct area and flow rate, at
the point of Static Pressure measurement.
3.4 Area Factor (A k). An empirical factor of an outlet or
inlet, ft2 [m2], determined from the discharge or intake 3.12 Published Rating. A statement of the assigned values
velocity (Vk) and the volume flow rate, Q, cfm [m3/s]. of those performance characteristics, under stated Rating
Conditions, by which a unit may be chosen to fit its
Q ⎡ L s⎤ application. These values apply to all units of like nominal
Ak = ⎢ Ak = ⎥ size and type (identification) produced by the same
Vk ⎣ Vk ⎦
manufacturer. As used herein, the term Published Rating
includes the rating of all performance characteristics shown
3.5 Aspect Ratio. Ratio of the length/width of a on the heat pump or published in specifications, advertising
rectangular air outlet. or other literature controlled by the manufacturer, at stated
Rating Conditions.
3.6 Discharge or Intake Velocity (Vk). The average of the
velocities of the air stream, fpm [m/s], of an outlet or inlet, 3.12.1 Application Rating. A rating based on tests
measured at specified locations relative to the face of the performed at Application Rating Conditions (other
outlet or inlet with a specified instrument. than Standard Rating Conditions).

3.7 Flow Rate. The volume of standard air per unit of 3.12.2 Standard Rating. A rating based on tests
time, cfm [m3/s], which moves past a given plane. performed at Standard Rating Conditions.

3.8 Hertz (Hz). A unit of frequency equal to one cycle per 3.13 Rating Conditions. Any set of operating conditions
second. under which a single level of performance results and which
causes only that level of performance to occur.
3.9 Neck Velocity (Vn). This is measured in fpm [m/s] and
is calculated as follows: 3.13.1 Standard Rating Conditions. Rating
Conditions used as the basis of comparison of
Q ⎡ L s⎤ performance characteristics.
Vn = ⎢Vn = ⎥
An ⎣ An ⎦
3.14 "Shall" or "Should". "Shall" or "should" shall be
interpreted as follows:

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 ARI STANDARD 890-2001

1. Fixed
3.14.1 Shall. Where "shall" or "shall not" is used 2. Adjustable
for a provision specified, that provision is mandatory
if compliance with the standard is claimed.
Section 5. Test Requirements
3.14.2 Should. "Should" is used to indicate
provisions which are not mandatory but which are 5.1 Test Requirements. Diffusers and Diffuser
desirable as good practice. Assemblies shall be verified by tests conducted in
accordance with the provisions set forth in ASHRAE
3.15 Sound Power Level, Lw. This is ten times the Standard 70. One exception is that the single stationary
logarithm to the base ten of the ratio of the sound power microphone provision, as defined in 5.2 of ASHRAE
radiated by the source to a reference sound power, expressed Standard 70, shall be disallowed and the room qualification
in decibels (dB). The reference sound power used in this shall be in accordance with ANSI Standard 12.31.
standard is 1 picowatt (pW).
For the purposes of this standard, the highest sustained
3.16 Standard Air. Air weighing 0.075 lb/ft3 [1.2 kg/m3] velocity shall be the average velocity determined for a
which approximates dry air at 70°F [21°C] and at a period of not less than 30 seconds.
barometric pressure of 29.92 in Hg [101.3 kPa].
5.2 The procedures of Section 6 shall be used where
calculation procedures are required to develop the Standard
Section 4. Classifications Rating.

4.1 Classifications. Normally, Diffusers and Diffuser

Assemblies falling within the scope of this standard shall be Section 6. Rating Requirements
classified as one or more of the following types:
6.1 Standard Ratings. Standard Ratings shall be
a. Plenum Slot Diffusers (with integral factory- established at the Standard Rating Conditions specified in
mounted plenum) 6.3.

1. Fixed 6.2. All Standard Ratings shall be verified by tests in

2. Adjustable accordance with Section 5.
3. Fire Rated
6.2.1 Values of Standard Ratings. Standard
b. Round Diffusers Ratings relating to air flow rates shall be expressed in
cfm [m3 /s] of Standard Air and stated as follows:
1. Round Inlet/Round Face
Rate to
c. Perforated Diffusers (perforated panel face) Range,
Nearest, cfm
cfm [m3 /s]
1. Face-Mounted [m3 /s]
2. Neck-Mounted 0 to 49 [0 to 24] 1 [0.5]
50 to 199 [25 to 99] 5 [2]
d. Louvered Face Diffusers (horizontal pattern) 200 to 999 [100 to 499] 10 [5]
1000 and over [500 and over] 25 [10]
1. Fixed Blades Non-Adjustable
2. Fixed Blades Adjustable Pattern
Isothermal Throw shall be expressed to the nearest
3. Adjustable Blades
1 ft [0.3 m].
e. Square Diffusers
Static Pressure shall be expressed to the nearest 0.01
in H2O [2.5 Pa].
1. Fixed Multiple Cone
2. Fixed Panel or Single Cone
Discharge Sound Power Level shall be expressed to
3. Adjustable Multiple Cone
the nearest 1.0 decibels.
4. Adjustable Panel or Single Cone
6.3 Standard Rating Conditions. The conditions of test
f. Linear Diffusers (with factory provided
for Standard Ratings shall be as follows:
plenum)
Inlet Neck Velocity.......…………...........750 fpm [3.8 m/s]

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ARI STANDARD 890-2001

Exception: Where this velocity is outside the manufacturer's Octave Band Center Rating Tolerance,
recommended velocity, the unit shall be tested at the Frequencies, Hz dB
manufacturer's rated point. 125 6
250 4
Terminal Velocity.......………................150 fpm [0.76 m/s] 500 3
1000 3
6.3.1 Air flow rate shall be determined at the 2000 3
Standard Rating Conditions. 4000 3

6.3.2 Static Pressure shall be measured at the

Standard Rating Conditions. Section 7. Minimum Data Requirements for
Published Ratings
6.3.3 Discharge Sound Power Level (in dB
reference to 10-12 watts) shall be determined at the 7.1 Minimum Data Requirements for Published Ratings.
Standard Rating Conditions, when installed in As a minimum, Published Ratings shall include Standard
accordance with Figure 7 or 8 of ASHRAE Standard Ratings and Part-Load Ratings (where applicable). All
70. claims to ratings within the scope of this standard shall
include the statement "Rated in accordance with ARI
6.3.4 Isothermal Throw shall be measured at the Standard 890". All claims to ratings outside the scope of
Standard Rating Conditions. this standard shall include the statement "Outside the scope
of ARI Standard 890". Wherever Application Ratings are
6.4 Application Ratings. Ratings at conditions other than published or printed, they shall include a statement of the
those specified in 6.3 may be published as Application conditions at which the ratings apply.
Ratings, and shall be based upon data determined by the
method of testing described in Section 5. Published Ratings shall include Standard Ratings and may
also include Application Ratings. As a minimum, the
6.5 Publication of Ratings. Wherever Application following information shall be published:
Ratings are published or printed, they shall include or be
accompanied by the Standard Rating, clearly designated as a. Air flow rate, cfm [m3/s]
such, including a statement of the conditions at which the b. Static Pressure, in H2O [kPa]
ratings apply. c. Discharge Sound Power Level, dB (second
through seventh Octave Band)
6.6 Tolerances. To comply with this standard, Published d. Isothermal Throw, ft [m]
Ratings shall be based on data obtained in accordance with
the provisions of Sections 5 and 6 of this standard, and shall
be such that any production unit, when tested, will meet Section 8. Marking and Nameplate Data
these ratings within the following tolerances:
8.1 Marking and Nameplate Data. As a minimum, the
6.6.1 The isothermal throw to 150 fpm [0.76 m/s] packaging of each Air Diffuser and Air Diffuser Assembly
(Terminal Velocity), determined from tests per shall display the manufacturer's name and unit model
ASHRAE Standard 70, Section 6.4.4, shall be within designation.
± 20% or 1 ft [0.3 m] whichever is greater, of the
published value.
Section 9. Conformance Conditions
6.6.2 Static Pressure shall not be more than 110%
of the Published Rating. 9.1 Conformance. While conformance with this standard
is voluntary, conformance shall not be claimed or implied
6.6.3 Discharge Sound Power Level shall not for products or equipment within its Purpose (Section 1) and
exceed the published values in each Octave Band by Scope (Section 2) unless such claims meet all of the
more than the rating tolerance shown: requirements of the standard.

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 ARI STANDARD 890-2001

APPENDIX A. REFERENCES - NORMATIVE

A1 Listed here are all standards, handbooks and other A1.3 ARI Standard 880-1998, Air Terminals,
publications essential to the formation and implementation 1998, Air-Conditioning and Refrigeration Institute,
of the standards. All references in this appendix are 4301 North Fairfax Drive, Suite 425, Arlington, VA
considered as part of the standard. 22203, U.S.A.

A1.1 ANSI Standard S1.11-1986 (R1993), A1.4 ASHRAE Standard 70-1991, Method of
Octave- Band and Fractional Octave-Band Analog Testing for Rating the Performance of Air Outlets
and Digital Filters, 1993, American National and Inlets, 1991, American Society of Heating,
Standards Institute, 25 West 43rd Street, 4th Fl., New Refrigerating and Air-Conditioning Engineers, Inc.,
York, NY 10036, U.S.A. 1791 Tullie Circle, N.E., Atlanta, GA 30329, U.S.A.

A1.2 ANSI Standard S12.31-1990 (R1996), A1.5 ASHRAE Terminology of Heating,

Precision Methods for the Determination of Sound Ventilation, Air Conditioning and Refrigeration,
Power Levels of Broad-Band Noise Sources in Second Edition, 1991, American Society of Heating,
Reverberation Rooms, 1996, American National Refrigerating and Air-Conditioning Engineers, Inc.,
Standards Institute, 25 West 43rd Street, 4th Fl., 1791 Tullie Circle, N.E., Atlanta, GA 30329, U.S.A.
New York, NY 10036, U.S.A.

APPENDIX B. REFERENCES – INFORMATIVE

The following Recommendations have been made by the ISHRAE Standard Committee to
be incorporated in the Standard:-

1. Minimum Material specifications for Construction of Diffusers and Dampers – to be

included in the Standard.
2. Noise level in the room for Diffusers with Damper (at 25%, 50%, 75% and 100% open)
and without Damper – to be included in the Standard.
3. ANSI/ASHRAE 70-1991 to be a part of the Standard.
4. The Standard ARI 890-2001 does not cover Grilles and Registers. Propose to have one
Standard which covers Diffusers, Dampers, Grilles and Registers.
5. Room attenuation to achieve the specified noise levels as per the application / usage of
space should be a part of this Standard.

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