As a result of the current concern of ecology and noise pollution in rural areas, ventilation of livestock buildings is being criticised for its noise contribution. Consequently great efforts are done to reduce the noise production of axial fans, as commonly used for ventilation of agricultural buildings. Such axial fans that have been designed to move very large volumes of air in relatively short periods of time comprise a multi-bladed rotor driven by a relatively high-speed electrical motor. Because of the high rotational speed , relatively high noise levels are generated. An adequate noise reduction method is to provide acoustic damping in the housing structure. Another approach is to reduce the rotational speed by improving ventilation control strategies. The latter approach was considered in our study. The sound power levels produced in a test set-up in a reverberation room were measured following the standardised procedure ISO 3741:1999. The sound production of an axial fan (fan blade diameter 500-mm) was measured at different levels of rotational speed (varied between 200 and 1400 rpm). It was found that the total sound power level could be reduced from 80.1 dB(A) at full speed to less then 60 dB(A) at 20% of its maximal speed. Based on these findings a ventilation control strategy was developed that reduced the noise production with about 20 dB(a) during night-time.
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