Smart Ductwork

In ventilation and piping systems, noise from fans, air control dampers and other components travels through the air ducts. At the same time, the air should be guided with as little pressure loss as possible. Rounded duct bends have lower pressure losses than 90-degree elbows and therefore create less turbulence and noise. The noise from the fans, dampers and so on, however, remains.

An additional silencer takes up space and can increase the pressure loss. In retrofits in particular, conventional silencers with porous material are very heavy and need dedicated clearances and mountings. What was needed was a way to reduce noise within the existing duct routing without significantly changing the geometry of the bends. Ideally, the optimisation would also need little material, keep costs as low as possible and pay for itself through lower OPEX within less than three years.

Step 1: Rounded bends are without doubt better than 90-degree elbows. In a laboratory test, rounded, smooth bends were therefore lined with a piece of ABSORA-sheet exactly in the deflection zone. In a test setup, one, two and three consecutive rounded bends were replaced step by step with bends featuring ABSORA-sheet.

The geometry remained almost the same. What was compared was therefore the effect of the change of material, not the effect of a different bend shape. The pressure losses of the compared designs were also almost identical and within tolerance.

Step 2: Smooth guide vanes in duct bends are known to optimise pressure losses as well when they are placed in the middle, at the right spacing and with other parameters taken into account. This lowers the pressure loss once more compared with a rounded bend.

The smooth guide vanes were replaced with guide vanes made of ABSORA-sheet. This showed that specific peaks — such as the 300 Hz peaks of fans — can be targeted in the same way.

With three ABSORA bends, the sound level in the lab fell by 4.8 dB(A). Under these measurement conditions, that corresponds to a reduction in sound intensity of about 67%.

If both the rounded bend and the guide vanes are made of ABSORA-sheet, a great deal can be gained per bend — more than many thought possible.

The test shows that the effects of several bends add up. Most HVAC duct systems consist of many bends. This means several absorbers can be saved — absorbers that also count as hazardous waste when disposed of. At the same time, the pressure loss can be lowered so much that less electricity is needed, so the solar system on the roof may already be enough to run the system.

In customer applications, too, reductions of 2.7 to 4.0 dB(A) per bend were measured, depending on design and operating conditions. Depending on the number of bends, many dB(A) can therefore be reduced in total. The solution is already used in several series products.

In 1960, DARPA and NASA, together with Northrop Grumman, researched an aircraft that used micro-perforations to reduce flow losses by having large vortices absorbed, as it were, by small ones. The project was successful and achieved 25% fuel savings. Its drawbacks, however, were the costly manufacturing in stable sheet metal and the cleaning. This is where ABSORA has found a solution.

The aim today is not only to make wings quieter and more aerodynamic, but also to upgrade old systems such as ducts, where no one thought it possible.

On request, our partner Ferrum Lasercut can manufacture and deliver an ABSORA-sheet cut to fit. One square metre currently costs 40 euros plus laser costs.