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was unnecessary for the pressure to power conversion. If near field sound pressure levels are needed, then the physical size of the source must be taken into account by using Eq. 2.91.

Air Cooled Condensers

In single or multifamily residences, air cooled condensers are used in place of the larger cooling towers or evaporative condensers. The noise from these units is due to the fan, usually a propeller type, with a small contribution from the air flow through the condenser coil decks. Figure 13.5 shows a sketch and measured data. These data are for a 3-5 ton residential unit based on sound pressure levels measured at 6 ft from the center of the fan and at 90° to the direction of airflow, which is out the top of the unit.

Pumps

Pumps are found in virtually every building. When they are located above grade they are best mounted on an inertial base and housekeeping pad, such as that in Fig. 13.6. Pipe elbows that are connected to the pump should be supported from the isolation base. Flexible couplings are used to compensate for pipe misalignment and to provide structural decoupling. Piping should be resiliently supported in accordance with the recommendations given in Chapt. 11.

Noise in Mechanical Systems Figure 13.5 Sound Power Levels from a 3-5 Ton Air Cooled Compressor

Figure 13.6 Water Pump Installation with Inertial Base

Note that the piping is supported off the inertial base.

Figure 13.6 Water Pump Installation with Inertial Base

Note that the piping is supported off the inertial base.

Sound pressure level data at a distance of 3 ft have been published by Miller (1980) and are reproduced in Table 13.4. Also shown in the table are the corrections to be subtracted from the overall level to obtain the octave band values. A-weighted levels are 2 dB lower than the overall levels.

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