The real performances of ventilation systems on site remains a challenge in practice. One of the most common reasons for complaints by the building occupants is the acoustic discomfort. Mechanical ventilation often produces too high levels of noise, mainly coming from the fans.
Although several good practice recommendations are theoretically known to limit the noise generation by mechanical ventilation systems, the acoustical performance of real ventilation systems on site seems uncontrolled and unexpected.
This paper presents a case study for the optimisation of a mechanical ventilation system in a dwelling. The aim was to identify points of attention for the improvement of both the acoustical and electrical performance of the system in practice.
The noise levels in the dwelling as well as the power input and the flowrates have been measured before and after several steps of optimisation of the ventilation system. The fan and the ductworks remained mainly unchanged.
The noise levels measured in the dwelling before the optimisation largely exceeded the requirements of the Belgian standard NBN S 01-400-1, for example 42 dB in the living room against 30 dB required.
After all the optimisation steps, the noise levels as well as the power input of the system significantly decreased. The main sources of improvement have been identified as the removal of acoustical dampers in the duct behind the air terminal devices, the replacement of externally mounted air transfer devices and air terminal devices with lower pressure drops, and better adjustment of the air terminal devices. Adding primary sound attenuator to the part of the ductwork which was not yet equipped allowed to further improve the acoustic performances in the rooms.
This case study demonstrated that large improvements of the acoustical and electrical performances of the mechanical ventilation system were possible with only limited modifications and keeping the fan and the ductwork mainly unchanged.