Ventilation without noise - Acoustic window control

© Fraunhofer IBP
© Fraunhofer IBP

Evaluation of the annoyance caused by various traffic noises with closed, opened and automatically controlled window.

Whether at home, at work in the office or in a hotel – we always face the same problem: We open the window to let fresh air in, but immediately find out that the outdoor noise (noise from traffic, construction, etc.) is too loud, so that we need to close the window again after just a short time. At night this is even more annoying, for example if the pass-by noise of a train disturbs the sleep. A new technical development of the IBP Acoustics Department designed in co-operation with enterprises counters this problem. The development is based on automatically controlled windows that are already ensuring good ventilation, opening automatically if ventilation requirement is recorded by sensors. An entirely new function ensures having “an ear close to the window” which ensures closing the window automatically as soon as a certain exterior noise level is reached. When, for example, the train has passed, the window reopens and again supplies fresh air to the room.

The technical implementation of the acoustical window control is based on a simple basic principle: The external noise impact is measured by a microphone or any other sound sensor being integrated for example externally into the window frame. If the noise level exceeds the value set by the user, the window will close automatically, and if the value is deceeded, it will reopen again. The automatic control can be used both for tilt windows and windows with parallel action function, but also for roof windows and skylights. There are, of course, further requirements and functions to be taken into account. At continuous noise for instance, it will have to be decided to give priority to either the need for quietness or to the ventilation requirement. In addition, security aspects are to be ensured as well. It is the user who finally decides on how to operate the system.

As drives for automatically controlled windows are already available on the market, the IBP mainly focuses on the development of sensors, control systems, and on quietly working drive systems. Despite the simple principle there are numerous criteria and boundary conditions to be met with respect controls, such as

  • consideration of short-term noise peaks,
  • consideration of the indoor sound level,
  • signal detection for an anticipatory control behavior,
  • integration of schedule information (railway, airports).

Further points may be added in order to realize a most flexible and comfortable control. On the other hand, a simple system turned out to be already sufficient in many noise situations to noticeably reduce the noise impact in the affected rooms, particularly the high temporary impact of train and aircraft noise with intermediate quiet periods. The impact of the automatic control was evaluated both technically and by tests carried out with test persons who were exposed to different sound events (ICE, freight train, helicopter) presented to them in a room with closed, opened and automatically controlled windows. The test persons assessed the noise scenarios i. a. with regard to annoyance and loudness.

The results confirmed the assumptions: The perception of noise in a room with acoustically controlled windows is similar to the noise perception with permanently closed windows. Compared to this, the noise with open windows was perceived to be significantly louder and more annoying. The test design also allows for further conclusions. As the application context is of significant importance for an acoustic window control, the test persons were devided into a “relaxed” group and a “cognitive” group. In a quiet and relaxed situation at home for example, the outdoor noise will be perceived to be much more annoying than in a cognitive situation, for example at work. All these findings will be included in the control methods in order to be able to finally offer a solution that is suitable for as many applications and users as possible. There are numerous interested parties even though the control offers hardly any benefits for continuous noise and short-time noise peaks. Thus, the next steps on the way to practical use are evident to provide the best combination of natural ventilation and quietness for people in noise-exposed areas.