Design and Fabrication of an HVAC Test Stand for Active Noise Cancellation Comparison

The noise generated by air handling equipment in large HVAC systems can be distracting, and even damaging, to those working in open office spaces and large industrial buildings. Traditionally, these noise problems have been mitigated using passive solutions, such as duct silencers and liners, but these systems are bulky, making it difficult to retrofit older buildings, and they are also not a viable option in highly regulated areas where fibrous materials pose a hazard. A new type of loudspeaker, the carbon nanotube (CNT) thermophone, has been developed as a coaxial solution to provide active noise control within HVAC ducts to overcome the limitations that are seen with traditional passive noise control solutions. To provide a platform to showcase this technology, a test stand has been developed to compare the cancellation of the CNT loudspeaker to that of a traditional duct silencer and to test the performance of an active noise cancellation algorithm that has been developed specifically for this new type of speaker. The design parameters will be discussed for both the test stand and the active noise control algorithm, including the selection of a duct fan based on acoustic characteristics, and preliminary active noise cancellation data will be presented.