Karakterisering och beräkning av ljudkällor i fläktrumsamt dess transmission

Abstract: The performance and sound emission of a fan is strongly influenced by the installationeffect, which can be defined as the difference between the performance of a fan in ainstallation and the ideal configuration of the same fan. The factors that one should keepin mind while designing a fan system are many, but if some ground rules are followed thenoise can be drastically reduced. The choice of location for the equipment in the buildingis a critical decision and a less ideal location can result in expensive reconstructions and,or that spaces around the fan room can not be used for its initial purpose. A large fan withlower rotation speed will have lower sound emissions then a smaller fan with a higherrotation speed, for the same air flow. The sound and vibration emissions, as well as theenergy consumption of the fan will be at its lowest values when it is at its point ofmaximum efficiency. The outlet configuration of the duct from the fan should be straightand without dampers or ducts silencers that can create turbulence or a higher staticpressure close to the fan, which will decrease the fans performance drastically.The vibration isolation of the fan should be created and specified for the specificinstallation and not solely the fan characteristics. Proposals to predict and measure thestructure-borne sound pressure and transmissions in buildings have recently beenreleased. With a standard over the structure borne sound, the manufactures can declarethe source data for the fans under different operations. This brings that more accuratepredictions and calculations of the structure borne sound from installations can be done.Earlier calculation methods show big deviances between measured and calculated soundpressure in several cases. Above all the spread of the results is large, which makes themethod somewhat unreliable when sound rating spaces, regarding fan room noise.Calculations and predictions of the sound pressure in a fan room can, after proposals ofchange, be done with a deviation of 10 dBfor all frequencies between 63 and 4000 Hz.The method shows a tendency to overrate the sound pressure with a relatively smallspread of the results. It also shows signs to be able to predict the sound pressure in fanrooms with smaller fans then big fan units.Calculations of the increase of sound pressure that occur in the cavity between the floorstructure and the fan unit show big deviations it if is done for specific frequencies.However results show that calculations of the total sound pressure can be done with abetter accuracy.