Noise Pollution
Submit manufacturer’s latest published data for dimensions, materials, installation details and certified sound performance tests according to ISO 7235:1991(E) Standard.
Certification data for pressure drop and static and dynamic insertion loss based on tests of offered attenuator. The dynamic insertion loss shall of at least three different air velocity and the highest tested shall not less than 8m/s.
Submit airway velocity together with the face velocity of the offered attenuator and the airway velocity shall not exceed 11 m/s at any level of the specified Noise Criteria (NC) condition. However manufacturer shall control the air way velocity and not only the fan velocity at the offered attenuator to the proper level as related to the individual NC level specified.
Noise levels, due to equipment and ductwork, to permit attaining sound pressure levels in all 8 octave bands in occupied spaces will conform to the following NC curves as shown in table. Schedule of Design Criteria for Noise Levels of the Designated Rooms.
The specified noise level limits shall apply to every position of 1.5m from first outlet or equivalent.
A detail sound calculation including duct system insertion loss, Room Reverberant, Directivity and Resultant 8 octave bands Sound Level before and after the attenuator (if any) to submit for approval on every individual system.
Silencer
Manufactured and supplied as a complete factory pre-fabricated unit.
The outer casing shall be fabricated of galvanized steel of minimum 1mm thick for rectangular silencer and minimum 1.0mm thick for circular silencer. Seams shall be locked formed and mastic filed. Minimum 60 kg/m3 density Rockwool packed under 5 percent compression and minimum 50mm thick.
Internal Construction:
- Galvanized Perforated Steel Sheet: Minimum 0.4mm thick between 10% and 40% open area. The splitters shall have sheet metal nose cone.
- Insertion Loss Rating: Sound attenuators shall be selected to meet the specified NC levels, taking into consideration the generated from the proposed equipment, the room acoustic and the specified pressure drops of the sound attenuators, generally not exceed 50 Pa.
Acceptable Noise Criteria Levels:
Environment / Room
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Acceptable Level (Noise Criteria)
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Churches, Theatres, Mosque
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NC 25-30
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Cinemas
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NC 30-35
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Hospital Wards, Homes
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NC 25-35
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Private Offices, School Rooms
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NC 30-35
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General Offices
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NC 35-45
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Mechanized Offices
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NC 40-50
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Restaurants, Bars, Canteens
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NC 35-45
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Department Stores, Shops
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NC 35-45
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Swimming Baths, Sports Arena
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NC 35-50
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Kitchen & Bathroom
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NC 40-45
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Factories
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NC 45-70
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Basement Car park
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NC 50-60
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Living & Dining & Study
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NC 35-40
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Bedrooms
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NC 30-35
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