ebm-papst Fans, Blowers and Technology

Turbulence. It happens. Luckily, ebm-papst has a solution for noisy systems.

If you’ve tossed and turned at night, unable to sleep because of humming sounds from your home’s air conditioner, you know these noises are intolerable. That same distraction from a heating or A/C system can strike anywhere… in the office, at the store, at a restaurant.

But did you know that it’s usually the turbulence in an air-moving system – not the components – that makes your ears ring?

Fans are an essential part of today’s refrigeration, air conditioning and ventilation systems.  They are designed and tested to minimize noise in thousands of applications. However, there are wide differences in how fans are installed and configured, the conditions in which they operate, and their location within the air system. These variables can create air inflow and outflow disruptions that raise the ‘loudness level.’

For example, the housing walls of rectangular heat exchangers can generate a backflow that creates pressure fluctuations on the fan blade. These turbulence ‘vortexes’ drastically increase a fan’s low-frequency (tonal) noise. While it’s not possible to compensate by changing the fan itself, it is possible to straighten the flow of air moving into the fan and balance the pressure of air moving out of the fan.

Over the past few years, ebm-papst has developed two passive add-on devices — the FlowGrid air inlet grill and the AxiTop diffuser. In distinctive ways, each improve how air moves into and out of our axial and centrifugal fans.

The FlowGrid air inlet grill has a straightening effect on the inflowing air, reducing acoustical levels and considerably reducing tonal noise.

In a condenser application, fitted with an axial fan, the FlowGrid air inlet grill reduces overall sound levels by 3.9 dB(A) and tonal noise by 16 dB. In a low profile (250 mm diameter) air conditioning device, the FlowGrid reduces sound levels by 2.5 dB(A) and reduces tonal noise by 9 dB.

While FlowGrid works to reduce low-frequency noise on a fan’s inlet side, the AxiTop diffuser reduces mid-frequency noise on the fan’s discharge side. How does this work? AxiTop operates like a reverse nozzle, increasing pressure and significantly reducing discharge losses. Efficiency increases and operating noise decreases.

Using both AxiTop and FlowGrid on a condenser fitted with a 31.5 inch (800 mm) axial fan, with outside air drawn through a heat exchanger, we’re able to reduce the fan’s noise level by 5.8 dB(A) and tonal noise by 20 dB.

Setting new standards for their quiet, energy-efficient operation, both devices are advancing technology and creating ideal operating conditions for fans. As a result, we can all sleep better!

Contact our application engineer for additional information at 860 674-1515 or by e-mail at sales@us.ebmpapst.com.

Compact, efficient FlowGrid air-inlet grill from ebm-papst  significantly reduces noise spectrum for
axial and centrifugal fans

Whether it’s heat pumps in the home, condensers in supermarket refrigerators or ventilation systems on the production floor, FlowGrid, the innovative patent-pending air-inlet grill from ebm-papst, is dramatically reducing noise levels for fans installed within limited-space air moving equipment.

What our award winning AxiTop diffuser does on the pressure side (outlet)
of the fan, FlowGrid does on the suction side (inlet). Easily mounted to applications with ebm-papst fans and backward curved impellers, its open grill design straightens airflow to minimize turbulence before the air hits the axial or centrifugal impeller blades. FlowGrid is ideal for fans installed within flat and central air handling units, air purifiers and heat pumps with centrifugal fans, or air-water heat pumps, condensers and V-shaped condensers
with axial fans.

“FlowGrid is the result of our extensive airflow testing for inlet conditions with a wide variety of customers’ axial and centrifugal fans across dozens of applications,” said George Riker, business development. “By improving the aerodynamic conditions external to the fan, FlowGrid reduces the adverse effects of these inlet conditions and
minimizes noise.”

Here’s how noise happens within a fan and how FlowGrid corrects it:

1. When the walls of a device such as an air handler, heat exchanger or heat pump are different distances from the fan, powerful vortices combine in the narrowest areas to form so-called ‘vortex strings.’

2. These turbulences then hit the rotating blades of the fan, generating noise – specifically a broadband noise and additional narrowband, tonal frequency components, known as propeller noise or tonal noise.

3. Mounted on the air intake side of the fan, the FlowGrid weakens these ‘vortex strings’ as they flow through the device.

4. This reduces sound pressure across the entire sound frequency range and especially in the low frequency tonal range.
   
   

Apart from reducing overall sound pressure, the most drastic reduction is in low-frequency blade-passing noise (the sum of the fan speed and the number of blades) caused by blades cutting through turbulence within small space applications such as heat exchangers. The FlowGrid grill has been proven in certain applications to reduce overall sound pressure levels by as much as 3.9 dB(A), and these blade passing frequencies by up to 16 decibels.

With FlowGrid, ebm-papst is making a clear contribution to passive noise reduction – a big part of our GreenTech philosophy. It can help manufacturers and ventilation specifiers comply with noise regulations and improve the environment for employees who work near ventilation equipment. The innovative air-intake grills, which require less acoustic insulation, work with both axial and centrifugal fans without reducing their performance. Using them can help to reduce or entirely avoid the use of cost-intensive, active noise-reduction measures.

For additional information about how FlowGrid can make a difference in your application, contact one of our application engineers today at 860 674-1515 or sales@us.ebmpapst.com.