Thinking inside the box: a cost-effective approach to fan array noise reduction

Noise from fan arrays can contribute high sound pressure levels both to buildings and communities. Noise that travels from these units through ducts and into the spaces within buildings can be attenuated with silencers or duct lining. However, sound radiated from the unit through building structures or into communities can be more difficult to attenuate and often adds significant cost. While it is possible to attenuate sound from the unit using enclosures or sound walls, exploring the operation of the fan arrays themselves could be a more cost-effective noise reduction method. One particular noise reduction method for an existing fan array was proposed for a customer: review sound levels of each fan within the array to determine how they are contributing to the radiated sound power level of the unit. The assumption that sound levels between individual fans within fan arrays are consistent is not always correct. A series of acoustical tests were completed; results indicated that sound caused by turbulent airflow within the tested fan array was able to be lowered by reducing the fan speeds of individual fans. By reducing the fan speeds of problematic fans and increasing speeds for the quieter ones within the same fan array, the same level of cooling can be provided with lower overall radiated sound levels at no additional cost.