| Abstract | Variable Speed Drive (VSD) motors allow building exhaust systems to operate more efficiently. It also, in principle, should lead to less noise due to a general reduction in fan speeds. Therefore, the National Research Council replaced old rooftop fans at one of its facilities, with fans selected for low-noise characteristics and equipped with VSD electric motors. Noise measurements were made on the roof of the building, at a distance of 5 m, with all three fans operating simultaneously and under identical controller conditions. The fitting of the acoustic absorptive lining was early in the investigation and not well documented. Anecdotal evidence comparing noise from the fans with lined enclosures to those with unlined enclosures, suggests that the differences were small and insignificant. A characteristic of this type of VSD controller is that noise is generated when high frequency components in the electrical power to the motor cause electromagnetic resonances in the stator of the electric motor. |
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