The noise from the Eurostar Nightstock HVAC module (140 had been built) was unacceptable in terms of overall noise and tonal content at the fan blade pass frequency. Conventional noise control techniques (silencers) from the manufacturer had been unsuccessful.
Maintaining the fan performance was critical and space within the air conditioning system was severely limited and a retro-fit solution was needed very quickly. The optimum solution involved a combination of Quiet Fan technology with a new 7 bladed impeller design that could be fitted very quickly at low cost and entirely within the existing HVAC unit i.e. no space implications. This reduced the annoying blade pass tone by 24dB and the overall system noise by 8dB(A).
As the fan noise reduction modifications reduced the noise at source, they simultaneously treated the intake, exhaust and break-out noise through the fan casing. Conventionally you would have needed separate attenuators for each transmission path that would have had a catastrophic effect on HVAC system performance.
The whole project was completed within a few days.