Zephyr S) Spécifications télécharger pdf (Page 18)

Since any mechanical power generates some sound energy

into the air, fans will create some noise. Because of the great

number of factors influencing sound output, it is invalid to

compare fans based on RPM, tip speed or outlet velocity.

The only accurate basis of comparison is the sound power

level generated by the fan at the required point of operation.

System designers use many methods to predict acoustic

acceptability of an occupied space. The A-weighted sound

pressure level provides a single number that corresponds

well to the human judgement of relative loudness. OSHA

bases requirements regarding exposure to noise on A-

weighted sound pressure levels. The disadvantage of this

method is that A-weighted sound pressure levels do not pro-

vide information as to the quality of the sound. Noise Criteria

(NC) curves are also widely used. To determine the NC level,

the sound power spectrum is compared to defined limits.

Other methods include RC curves, sones, SIL and Noise

Rating Curves.

Each method relies on sound pressure level information

because the human ear “hears” sound pressure fluctuations,

not sound power (Watts). Sound pressure is a function of the

attenuation of the space and the distance from the source.

Consider a 100 watt light bulb. It provides adequate light for

a closet, but not a classroom. And in a stadium it would be

imperceptible. While the light source was the same power

(100 watts), the brightness level changed dramatically.

Similarly, the same sound power level (acoustical energy)

produces greatly different sound pressure levels (noise).

In addition to sound power levels, PennBarry has provided

sone ratings to allow designers to make an educated judge-

ment as to the noise level a fan will develop in a space. Sone

ratings are a loudness index developed from sound power

level data. The calculation is at 5' from the fan inlet and in

front of a reflecting plane (hard wall). Sones are weighted

similarly to the A-weighing scale in that more weight is given

to frequencies that people hear “well” and less weight to fre-

quencies that people do not hear “well”. Another feature of

the sone scale is that it is linear rather than logarithmic. This

means that 40 sones is 33% louder than 30 sones, as

opposed to 40 dB being twice as loud as 30 dB.

Since the sone rating is determined from well defined

assumptions and is linear in nature, it is ideal for comparing

different fans moving air at the same CFM and SP. When

using sones for this purpose, differences of 3 sones are con-

sidered negligible. The suggested loudness level chart below

is a practical guideline for acceptable installed performance.

Sound power levels shown in this catalog were measured

and certified using AMCA Standard 300 Reverberant Room

Method for Sound Testing of Fans. The values shown are for

the eight octave bands defined in this standard, which agree

with ANSI 61.11-1986. One-third octave band sound power

levels are available upon request. The sound power levels

shown are rated in decibels (dB) using 10-12 Watts as a ref-

erence. The sone values shown in this catalog are based on

the sound power levels determined above, and calculated in

accordance with AMCA Standard 301 “Methods for

Calculating Fan Sound Ratings from Laboratory Test Data”.

Since any mechanical power generates some sound energy

into the air, fans will create some noise. Because of the great

number of factors influencing sound output, it is invalid to

compare fans based on RPM, tip speed or outlet velocity.

The only accurate basis of comparison is the sound power

level generated by the fan at the required point of operation.

Having sound power levels for a specific fan at a specific

operating point allows the system designer to determine the

theoretical sound pressure level at any point in the occupied

space. AMCA Publication 303 and the ASHRAE Guides pro-

vide more information on this process. Another use of sound

power levels is to compare similar fans. Generally differ-

ences of 6 dB in the 63 Hz band and 4 dB in all other bands

are considered insignificant. Sound power levels shown in

this catalog were measured and licensed using AMCA

Standard 300 Reverberant Room Method for Sound Testing

of Fans. Values shown are for the eight octave bands defined

in this standard, which agree with ANSI 61.11-1986. One-

third octave band sound power levels are available upon

request. The sound power levels shown are rated in decibels

(dB) using 10-12 Watts as a reference. Sone values shown

in this catalog are based on sound power levels determined

above, and calculated in accordance with AMCA Standard

301 “Methods for Calculating Fan Sound Ratings from

Laboratory Test Data”.

Sound Data Notes

Zephyr Fans

PENNBARRY

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Zephyr S) Spécifications Page 18

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