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Muffling noisy central heating systems

March 05, 2002

Droning noises generated by central heating boilers can aggravate good neighborly relations. Fraunhofer scientists have developed a compact sound attenuator for boiler exhaust vents. The active silencer employs electronics to damp noise emission.

During the cold season, the droning sound of the central heating is just one of an assortment of everyday background noises. "In general, most home owners don`t consider it a great problem", says Stefan Zimmermann of the Fraunhofer Institute for Building Physics IBP in Stuttgart. "However, in our experience, neighbors and tenants find the humming from behind the wall or from the chimney an extreme annoyance. It`s not uncommon that this leads to disputes, which can even end up in court." The noises in boiler exhaust vents are caused by turbulent air currents generated by the blower and the burning flame. This characteristic resonance of the blowpipe burner and the boiler unit can be clearly heard coming from the exhaust vent and the mouth of the chimney.

Until now, the attenuation of low frequency sound has required large silencers, for which there is usually insufficient space in the heating room. "In its place, we can offer a compact silencer of just half a meter in length, which achieves the same result as a conventional one measuring some three meters", emphasizes Zimmermann. "Together with the company Kutzner+Weber, we developed AKTIV PLUS. This system`s most important feature is its active working principle." The core element of the system is a compact metal case, which houses a loudspeaker, microphone and an amplifier, as well as the power supply. "With this equipment, we generate a sort of acoustic barrier, which prevents noise escaping from the burner", explains the project manager.

Not only are the active sound absorbers smaller than conventional porous or fiber-based systems. The modular principle developed by Kutzner+Weber also ensures that the sound attenuator can be installed virtually anywhere. Additional parts are used to suppress higher frequencies. Further advantages of the system: The new silencers are entirely maintenance-free. Since they are fully sealed against aggressive exhaust gas, they can also be used under low or high pressure. As the components inside the metal case are additionally protected by a special heat-resistant film, the system even works at temperatures of 200 °C without impairing attenuation.

Fraunhofer-Gesellschaft

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