Predicting the sound emission from airconditioning and ventilating systems

✍ Scribed by D.J. Croome

• Publisher: Elsevier Science
• Year: 1977
• Tongue: English
• Weight: 67 KB
• Volume: 10
• Category: Article
• ISSN: 0003-682X
• DOI: 10.1016/0003-682x(77)90015-9

✦ Synopsis

Further to the results published in 1976 ~ some more conclusions have been established.

Fan speed appears to be a more reliable predictor of room sound level than air speed. If air speed were used it would be difficult to judge which value to select for the calculation as there is a large variation throughout the system. The empirical formula was stated as sound level L in dB(A):

for fan speed N (rev/min). When N < 900 rpm this result gave L to + 5 dB for the ten installations used. Higher fan speeds give less reliable results. This research applied to centrifugal fans but Eck reports 2 some loudness measurements made by Zeller on a 450-mm diameter Pollrich axial-flow fan. The loudness-air volume characteristic shows that loudness depends on fan speed to within __+ 2 dB over a range of air volume flowrates extending from 0-4 to 2.4 m3/sec. Translating this work into the same form as that already reported 1 gives: or ,

1)phons

Now consider the effect of attenuation. Our experiments have shown that 0.5 dB/m is a conservative estimate which may be used in planning the distance between an airconditioning plant and the occupied space. Any straight sections which are less than 7 m in length between fittings should be ignored because an energy interaction prevails over this distance which disturbs the natural sound attenuation process. Suppose an attenuator with an insertion loss of~ dB is to be installed in a system in which there is a distance of D metres (less any straight runs under 7 m) 315