General

Contractor shall furnish and install prefabricated silencers in the air handling system of the sizes and performance shown on schedule and/or on drawings. They shall be the product of a nationally known manufacturer who has engaged in the manufacture and distribution of this type of equipment for at least 5 years.

Manufacturer shall, upon request, provide certified test reports from a NATIONALLY KNOWN QUALIFIED INDEPENDENT LABORATORY corroborating his cataloged performance. Test reports shall be based on a 24" x 24" cross sectional rectangular and/or 24" diameter tubular silencers of each type and model required for this project.

Manufacturer shall obtain prior product approval from the architect and/or consulting engineer not less than 10 days before bid date.

This specification is based on Silentair™ silencers as manufactured by SEMCO Incorporated.

Construction

Outer casings shall be of not less than 22 gauge galvanized steel construction. All external seams shall be lock-formed and filled with mastic, or continuously welded. Casings should be suitably stiffened to prevent permanent deformation when tested at 10" pressure differential. They shall not vibrate audibly during normal operation of air handling system.

Interior partitions shall be of not less than 24 gauge galvanized steel perforated to remove not more than 23% of the area. Acoustically absorptive filler material made from an inorganic fiber-glass material shall be compressed not less than 5% to eliminate voids and prevent settling. Material shall be vermin and moisture proof and impart no odor to the air.

Incombustible filler material shall exhibit not more than the following fire hazard classification values when tested in accordance with standard ASTM E84, NFPA 255 OR UL-723 test methods:

FLAME SPREAD: 25 SMOKE DEVELOPED: 50

Performance

Acoustical ratings shall be determined by the "duct-to-reverberation room" method as recommended in ASTM E-477. Tests shall be run both with and without air flowing through silencer at not less than three different flow rates. All ratings shall be based on test data from a NATIONALLY KNOWN QUALIFIED INDEPENDENT LABORATORY. Test method shall eliminate effects due to end reflection, vibration, flanking transmission and standing waves in the reverberant room. Airflow and pressure loss data taken in accordance with AMCA procedures shall be obtained from the same silencer used for acoustic performance tests.

Silencer shall provide the minimum attenuation values in terms of dB Insertion Loss as on the schedule at design air velocities.

The sound power level generated by self-generated noise airflow through silencer in dB re: 10-12 watts (PWL12) shall not exceed the scheduled values at design flow rates.

Aerodynamic Airflow pressure drop performance of silencer shall not exceed values indicated on schedule at the design air velocities.