Kitchen Extraction Systems

With the desire to locate restaurants and take away food outlets in town high street locations, noise breakout from kitchen fan extraction systems has become of paramount importance in terms of impact on nearby residential properties. Fan noise will reach the residential location by means of transmission from the end of the duct at roof level and breakout through the duct walls at lower level when mounted on external walls. Both these transmission paths need to be taken into account when predicting the noise levels at the residential flat. The calculation process requires sound power information from the fan supplier, which varies with frequency.

The known sound power level inside the duct downstream of the fan is firstly corrected for any silencer attenuation on route, then duct losses inside the duct bends and appropriate duct length, to give the internal sound power level at the point of interest. A knowledge of the sound reduction characteristics of the duct wall material, duct surface area and duct cross sectional then provides the sound power breakout values, which can be converted to sound pressure levels at the required distance from the duct. In the case of duct end outlet noise, further losses due to duct end reflection effects and directivity effects at the duct termination point need to be included in the sound power calculation, before conversion to sound pressure levels at the appropriate distance.

Restaurant and fast food outlets have been assessed in Bath, Bristol, Blandford, Faringdon and Clevedon.