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Abstract Background: In order to eliminate and reduce noise in predesigned and installed heating, ventilation, and air-conditioning (HVAC) systems, noise control in HVAC system areas needs to be performed using plenum chambers based on ASHRAE method. Methods: A plenum chamber made of galvanized iron was produced based on ASHRAE standards. The length, height, and width of the chamber were 1.5 meters, 1.1 meters and 1.2 meters, respectively. Two input and output openings (40 × 20 cm) were also made. The internal surface of the chamber was lined by 10 cm thick mineral wool with a density of 80 kg/m3. Findings: The results show a noise reduction of 2.3 to 13.2 dB with a peak at 250 Hz in 1/1 octave band frequency based on ASHRAE standard method. Generally, highest levels of noise reduction were observed in medium to high frequencies. Conclusion: The most important conclusion revealed by this study is that based on ASHRAE standard, dimensions of the plenum chamber and acoustic specifications of absorbent material applied into the chamber can highly affect the level of noise reduction. In fact, we can change the noise reduction value by changing the dimensions of the plenum. For low frequencies, as said before, it is better to use a bigger plenum chamber.

Keywords: Noise, Sound, Control, Ventilation, Plenum, Air duct.

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