Installation comments

1. In an installation where the fan and system are entirely within the space being considered (Figure 14.28), such as might be encountered in process work, local dust control systems, furnace cooling cycles, etc, the total sound is ra­diated to the space and the SWL values represent the total noise. If duct systems are installed on the fan discharge and inlet and the separate terminations are considered far apart, they should be calculated as separate sources. Each source can be considered as approximately 3 dB less than the total SWL of the fan, if separate data for inlet and outlet noise is not available.

The amount of sound radiated from the fan casing is gen­erally well below the fan inlet and outlet sound levels. It may however be required when calculating noise levels in plantrooms. If there is considerable absorption in the ductwork or system, the radiation could be a factor in the near field which is absorbed by insulating the fan.

2. Where the fan discharge (or inlet) has been ducted or con­nects directly to the outside space and the sound radiated through this section of the ductwork is not a factor in the determination of the sound pressure level in the space (Figure 14.29), the sound radiating from the non-ducted opening of the fan is one-half of the total sound. For duct­ed fans, this is the total sound power level SWL minus 3 dBW.

VOLUME FLOW FACTOR LqdB — to o f10 +20

■.» Ii.‘I… h‘il,| I ii HiMij I U-H iMft

0.1 0.2 0.5 1 2 S 10 20 50 100


Installation comments

Figure 14.28 Installation — fan and system within space

figure 14.28 installation — fan and system within space

Figure 14.29 Installation — fan discharge directed to outside space

figure 14.29 installation — fan discharge directed to outside space

Figure 14.30 Installation — fan connected to adjacent space

figure 14.30 installation — fan connected to adjacent space
Installation comments

Where the fan is connected to an adjacent space and sound is transmitted through the ductwork to the occupied space (Figure 14.30), the sound power level radiated from the inlet is used to calculate the resulting sound pressure level in the occupied space and is approximately equal to the total SWL values minus 3 dBW.


Octave band mid-frequencies — Hz

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