AI D3ST JBU r ION I JCT EAKAGE 1 :ST METHODS AND STANDARDS

To prevent the occurrence of leakage problems, the Consulting Engineer should include a duct leakage test section in the specification which would include a verification procedure and certification of tightness. In most cases it is not practicable for the test and balance agency to perform these tests as it would require having a test technician con­tinuously on the job as duct work is installed. From the standpoint of economy, i t is more practicable to have contractor conduct tests in accordance with AABC Test Standards, and have agency verify the r e ­sults obtained and issue a certificate. The test methods and procedures included in these standards are design ed for this type of operation. 4

The degree of air tightness in high velocity duct work should not be com pared with a water distribution system or gas system. Some degree of leakage wil l exist regardless of all the precautions taken during fabri­cation and installation, however, this leakage should be minimized to a degree that w i l l not cause excessive problems. Duct tightness can be determined by the application of proper pressure testing. When not otherwise specified, 1% of the system air volume at 1-1/2 times the duct operating pressure is considered reasonably adequate.

TEST EQUIPMENT In order to test sections of duct work as i t is installed, a portable means of testing is required. The most practical type of test apparatus which wil l facilitate field testing should consist of the following: A. SOURCE OF HIGH PRESSURE AIR:

1 . Rotary Type Blower Fan. 2. High Power Tank Type Vacuum Cleaner.

B. A DEVICE TO MEASURE TOTAL AIR FLOW ACCURATELY: 1. Calibrated Orifice Plate. . 2. Air Straightening Vanes. 3. Pressure Tap and Receptacle Tube

and Dampering Section. .

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C. INSTRUMENTS - TWO EACH: 1. Magnehelic Gage. 2. U - Tube Manometer. 3. Inclined Gage.

These items should be assembled into a portable device as shown in Figure One.

FIG. 1

TEST APPARATUS

FIELD TEST PROCEDURES

1. Seal all openings in duct section to be tested. , 2. Connect test apparatus to test section of duct using a

flexible duct connection or hose. 3. Close damper on blower suction side to prevent excessive

build up of pressure. 4. Start blower and gradually open damper on suction side

of blower.

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5. Build up pressure in the duct system being tested to the specified test pressure. (Use 1-1/2 times duct operating pressure if not specified.)

6. Read indicated pressure on instrument that is connected to section of duct under test. See Figure One.

7. Maintain this pressure for ten minutes which w i l l indicate audible leaks.

8. Repair al l visual and audible leaks. Shut down blower and release pressure when making repairs.

9. Upon completion of repairs, build up pressure to test pressure and read leakage pressure on instrument connected across test apparatus orifice plate. See Figure One.

10. Leakage CFM is read by consulting calibrated chart as shown in Figure Two. If no leakage exists, zero pressure differential w i l l be indicated.

11. Leakage factor allowable (1%) should be based upon the total oper­ating CFM of section of duct under test.

Figure Two (Next Page)

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SAMPLE CURVE I G . ? VARIATION OF AIR FLOW RATE WITH ORIFICE DIFFERENTIAL PRESSURE

T i l l , H E TTTT TTTT i m T I 2 IE n in" nr i i n ' m i TTTT nir D III nr D E" I T TTF • jam n i l . urn m rmr 3B T Li...

n 1—i fT =

n 1 5

=

=

-

1 . — "S i i g *

i & i

1 i

i

i n i i i i H i n i i i i i i i i i i i i i i i i H i i i P i i i u r m m i i i u i t m1.1 iai-'i»iiiiiiiiiiniiiiuiii)iuriuii'iii[iiiiniiii ' i '»«iiiB»iiiiiiiiiiiiiiiiiiiiiuiiff»iirtf IILIH.1-IHI1I

. 0 2 . 0 1 . O f . O t . . Ofl

TEST VERIFICATION

The air conditioning installation or sheet metal contractor shall engage the services of a Certified AABC Test Agency to verify test results and submit a certification certificate attesting to the results obtained. Arrangements shall be made between contractor and agency to co-ordinate the field test of installed sections of duct work. Test results and ver i f i ­cation shall be recorded and submitted on AABC standard test form number 32267. Tested sections of duct work shall be visually marked by agency with certification sticker and initials of field test inspector. Tests shall be made before duct sections are concealed.

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