Sound absorber for small centrifugal fans

WORLD – For over a year now, researchers at ebm-papst have been investigating how to ensure that high performance does not equate to high noise levels. Their solution has been to develop their FlowGrid for centrifugal fans which reduces the blade passing noise by 15 dB.
The air inlet grille is ebm-papst’s efficient noise protection measure for use in ventilation and air conditioning, patent pending. Up until now, the grille has been used on larger axial and centrifugal fans up to size 990. In recent times, ebm-papst has begun offering the sound absorber for smaller centrifugal fans with sizes from diameter 190 to 250 mm.
The problem is that noise and additional sounds arise when the inlet flow to the fan is disturbed, for example due to a narrow installation situation. This in turn leads to air vortexes, also known as vortex string formations, which create noise. The FlowGrid counters this problem by evening out these turbulences and dividing them into small portions before they hit the blades of the impeller. The grille on the intake side serves to reduce noise emissions and minimise disturbing individual frequencies. These narrow-band tonal noises, often referred to as propeller noise or blade passing noise, are consequently drastically reduced.
In tests on a size 190 centrifugal fan fitted inside a ventilation unit, the intake-side sound power level was reduced by over 2 dB(A) and the blade passing noise by 15 dB, simply by using an air inlet grille. Using these grilles can help to reduce or even entirely avoid the use of passive noise-reduction measures which are generally cost-intensive.
Unlike larger FlowGrid grilles, the smaller sizes of 190 to 250 are centrally locked, thereby combining optimal air conduction with contact protection as required per DIN EN ISO 13857 (“Safety of machinery – Safety distances to prevent hazard zones being reached by upper and lower limbs”). Consequently, this removes the need for an additional guard grille, which would negatively affect the intake flow.
The air inlet grille is made from robust compound material and is equally available in the 5VA material quality as per the UL94 flammability class. FlowGrid grilles for centrifugal fans in sizes 190 to 250 are used in a wide range of applications in ventilation and air conditioning, including flat air conditioners, central air conditioning units, air purifiers and heat recovery systems. The grilles are also used in cooling switching cabinets and inverters. Purchasers can now enjoy the perks of noise reduction in the low-frequency range, with the first sizes ready and awaiting delivery.