Fans are often installed in places where people work or live. The healthy limits of noise for these machines are below 55dB.
The reasons why fans make more noise than pumps are the higher speeds of the fluid that passes through the continuous flow part of the machine, the bigger dimensions and the thinner walls of the casing.
There are two major types of noise: aerodynamic and mechanical.
Aerodynamic noise arises in result of the influence of the flow on the elements that it comes into contact with. This noise is caused by the impeller high peripheral speeds, a change in the fluid direction and all kinds of vortexes.
Vortices are one of the main sources of vibration, oscillation and noise. The sound wave frequency and strength are different and depend on the speed and the change in pressure. Most often this type of noise reaches 120 dB.
Fans with higher pressure capability and those which blades are curved forward are quite noisier than those with backward curved blades. The fluid velocity of fans with forward curved blades is bigger compared to all other types. On the other hand bigger losses result in lower efficiency. And yet there is more friction, more vortexes and noise as well.
Mechanical noise
It is generated by vibrations of the fan and the pipeline walls, by ball and roller bearings, by gear and belt drives (if available).
Mechanical noise can be avoided during operation but aerodynamic noise is related to the construction, load and fan type.
Sound-absorbing materials are used to enclose the fan in quality HVAC and most of Geothermal manufactory equipment.
The noise in an installed distribution system is generated not only by the turbo machine mounted inside the heating equipment, but also by inaccurate dimensioning of air ducts, using elements for the system installation that are not suitable as well as incorrect selection and positioning of suction inlets of a system. |
