25 Years Ago, Active Control First Appeared as a Great Solution for Fan Noise - What has Happened?

F3 - Active Noise Control & Noise Analysis

The author first installed an active fan exhaust silencer at an industrial plant in 1987. There are now 11 units at the site, still operating, thus answering one of the fundamental questions at the time – that they are reliable. The superior low-frequency noise reduction, especially dramatic on tonal spectra, was clearly demonstrated. Compared against the alternative traditional passive silencers, the 1” (250 Pa) pressure loss savings leads to reduced fan power consumption that has recovered the original installation cost many times over.

In addition to reliability concerns, there are other factors that suppressed the wide application over the ensuing years: 1) the cost was high and the energy benefits not well appreciated; 2) initially, limited application know-how; 3) less stringent guidelines for acceptable noise levels – specifically a disregard for the annoyance of low-frequency noise and especially pure tones; and 4) now-expired fundamental patents in the hands of a few small companies who failed to sustain long enough for market success.

Along with the present low cost of the electronics, evolving market factors have increased the value of the benefits such that it is time for a fresh look at widespread use of this technology, especially in HVAC applications.

This paper highlights some of the 1000 installed units with which the author has direct familiarity, both industrial and HVAC, answering questions about performance predictability along with lessons learned. The systems over the years have provided exceptional low-frequency noise reduction while cumulatively saving approximately 30 million kW-hrs power consumption, with respective reduction of 20-35,000 tons of CO2. Low-noise, high-efficiency fan installations are an attainable goal for the future.