Remote Control of Noise by Email

A BP refinery in the USA had been quoted $1.25 million for five 1.5MW double entry ID combustion fan silencers to address the cause of extensive noise complaints. Their acoustic consultant had come across our aerodynamic fan noise control technology on the web and contacted us for advice. He sent his noise data to us by email and we identified that our technology would be ideal as an alternative to fitting fan silencers.

We used the information provided to design the aerodynamic modifications to generate drawings that would allow the components to be made by local contractors. After an installation process that required a tiny fraction of the downtime associated with fitting attenuators, the 180Hz blade pass tone had been completely eliminated (>12dB reduction), preventing any further noise complaints.

The quotation for fitting conventional silencers or mufflers totaled $1.25 million with additional costs associated with the extensive downtime required to fit the attenuators plus increased running costs.

The total project cost for all the aerodynamic modifications not only saved over $1,000,000 from the $1.25 million quotation for conventional silencers, but, in contrast with traditional mufflers, the modifications had no effect on fan efficiency (reduced running costs) and will last the lifetime of the fan with zero maintenance.

No site visits were required, saving time, resources and carbon (transatlantic flights etc). A very self-financing project...

More details of how to reduce ID fan noise using our aerodynamic noise control technology.

More information about our remote control of noise technology used for this ID fan project.

4 large axial extract fans caused noise complaints over a wide area in Canada, despite multiple attempts at noise control based on conventional techniques. One email led to the noise being reduced by 99% with no site visits required - the whole project was completed over the internet.

Mitchell, the site engineer sent us an email with smartphone video clips and photos. Soundtrack analysis showed the problem to be high-level tones at the 197Hz blade pass and harmonics. We used the photos to design retro-fit aerodynamic noise-reducing components which the client made and installed to give 20dB attenuation at 100m.

"We are exceptionally happy with the overall results that were obtained, from a noise reduction, cost, and time standpoint. INVC was very professional and prompt on all deliverables. Out of all solutions attempted this was by far the best and cost-effective. The whole process was very smooth from first contact to installation … glad we went with INVC, thanks…"

In addition to the attenuation of the primary fan hum sound, the harmonics and associated tones were also dramatically reduced as shown in this frequency analysis plot. Moreover, as the performance of the fans was also improved, the project was self-financing and will pay for itself in reduced running costs.

This technology is very applicable to all types of extract fans where tonal noise is an issue. As it is immune to the effects of the passage of materials or to corrosive atmospheres (it cannot clog), it is particularly suitable to attenuate the noise from fume, scrubber, dust, or other waste extract fans.

Wet wood pulp fan tonal noise

“I have never seen such an amazing result from a consultant in my career.”

Remote fan noise control, UK to New Zealand, no site visits... New wet wood pulp fibre bulk solids conveyor fans at the Pan Pac facility in New Zealand had caused noise complaints. The company made the very proactive “good neighbour” decision to shut down the plant overnight despite a substantial cost that posed a threat to the business.

“Shutting down 30% of our operation overnight was a significant cost and particularly damaging after the site was flooded and out of operation for over a year and needing investment of over $150M in the site flood repairs.”

Within exactly 3 weeks of googling the options and contacting INVC, noise from all 3 fans had been diagnosed, the solutions designed and installed with zero additional downtime. This resolved the problem and the plant was returned to 24-hour operation.

“On behalf of Pan Pac (and probably our neighbours as per this text) I would like to thank Peter Wilson and the INVC team for the professional service you have given and for helping overcome, in a very short time, a major threat to our business.”

“I have never seen such an amazing result from a consultant in my career. We were going down the acoustic insulation route before I “Googled”. I will call it lucky I found your website. Please make sure you pass on my thanks to your team!” Roger Jones, General Manager.

What fan noise attenuation technology made this possible?

Conventional silencers would not have been practical due both to the low frequencies involved and the passage of wet pulp solids that would have clogged any attenuators very quickly.

Locations: Pan Pac, New Zealand. INVC, UK offices

The 3 week process

1. Pan Pac googles “fan noise control”
2. Email to INVC
3. Smartphone video and fan details requested
4. Videos sent, analysed, problem diagnosed, costed proposal provided
5. POs received
6. Detailed recommendations designed and issued
7. 3 fans modified (using local engineers)
8. Plant returns to 24-hour operation
9. Neighbourhood happiness confirmed!

The diagnosis

The complaints were caused by fan blade pass hums at 89Hz, 95Hz and 280Hz from 3 different fans.

The solution

Designing bespoke aerodynamic inserts for each fan based on the fan geometries and flow paths. These were made locally in New Zealand (simple sheet metalwork) and welded into the fan volutes to reduce the turbulence causing the tonal noise at source.

This is a permanent, low-cost solution with no effect on performance that will last the lifetime of the fan without maintenance, despite the passage of wet pulp solids.

Conventional options?

Conventional silencers could never be practical for this application due both to the required length of around 10m and the fact that they would clog very rapidly. Acoustic lagging of the entire systems would have been very costly and caused problems with both maintenance and corrosion. Moreover, silencers would still have been required…

Solving noise complaints fast at minimum cost

Regulators and other organisations can take advantage of this outsourcing approach to eliminate noise complaints, knowing that the solution will be based on best practice that typically reduces project costs by 50% - 80%. Remote control of noise >>

Pan Pac

For over 50 years, Pan Pac Forest Products has been growing, processing and delivering wood products.

The Pan Pac Pulpmill produces up to 850 tonnes/day of Bleached Chemi Thermo Mechanical (BCTMP) wood pulp.

Pan Pac BCTMP is used in in the production of paper products including packaging boards, paper towel and paper. The Pan Pac Pulp markets include New Zealand, Australia, China, Indonesia, South Korea, Japan, Malaysia, Taiwan, Vietnam, India, and Pakistan. https://www.panpac.co.nz/

Download "The Remote Control of Fan Noise" guide >>

Attempts are often made to solve classic low-frequency chiller AHU fan noise using conventional silencers and noise barriers. Despite the fact that there is zero chance that these techniques can work at low frequencies, a fortune is still wasted every year on these useless palliatives. As air handling units (AHUs) on industrial sites, offices, supermarkets and other retail premises are such a common noise problem that you would expect better solutions based on a better understanding of the issues.

AHU noise control failings...

Previous failed attempts on this air-cooled chiller (48.5Hz and harmonics) were replaced with aerodynamic techniques that reduced the tones by 95% and improved the fan efficiency – all by email via forwarded video clips and photos.

The company had already tried using a barrier to mitigate the noise complaints to no avail. This is because barriers are almost completely ineffective at frequencies below around 200Hz (heard as drones, hums etc). Chiller and AHU fans regularly generate low-frequency tones as the blade pass hum often falls in this range. Whilst acoustic barriers and attenuators can be used to reduce the overall dB(A) noise level, they do not touch the low-frequency tones that are very commonly the actual cause of complaints. Our analysis of emailed video clips can immediately confirm whether this is the case, avoiding potentially costly mistakes. In contrast, our aerodynamic axial fan noise reduction technology addresses the low-frequency noise problem by reducing it at source with increased fan efficiency as a common additional benefit.

What are the air handling unit noise sources?

Typically, there are only 3 sources/types of noise generated by AHUs. They are:-

• Broadband air noise ("rushing sound") from the fans across a wide range of frequencies. This dominates the headline dB(A) noise level and can be attenuated by conventional silencers, barriers and enclosures. However, these can significantly reduce the system efficiency, adding to the cost.
• Low-frequency tonal noise ("hum or drone") at the blade pass frequency of the fans. These do not usually contribute anything at all to the overall dB(A) figure - and yet are a very common cause of complaints. They cannot be attenuated significantly using conventional means, the only effective solution is to use low-cost aerodynamic technology, technology that will often increase fan efficiency, reducing the cost still further (self-financing).
• Mechanical noise due to vibration transmitted into the support structure and then radiated as sound. Tonal at the motor speed and higher harmonics. The best solution is usually very low-cost retrofit high-performance damping.

When considering the options to reduce air handling unit noise, it is vital to diagnose the precise nature of the noise problem and which source(s) are responsible to avoid wasting money on the wrong solution. For example, the solution recommended by consultants to cut complaints re noise from roof-mounted AHUs in London was to replace one of the units with a quieter model. This cut the noise on the roof by 7dB(A). However, the complaints continued as they were caused by low-frequency fan tones from a different unit.

The lack of a correct diagnosis cost that client over £100k...

Click this link for more detailed information on the best approach to noise attenuation for chiller, air condenser, HVAC and refrigeration fans.

Cooling tower noise had triggered complaints as the noise was highly tonal. This led to a £31k quote from the supplier to replace the whole fan unit on the recommendation of their noise consultant. The local EHO suggested they contact us for a 2nd opinion.

We asked for a video clip by email, analysis of which allowed us to determine that the problem tone was at the tooth meshing frequency of the pinion gear. As a result, the gearbox was replaced at a cost of £3k. The whole process from 1st phone call to the provision of a detailed proposed solution took 6 hours…

This cooling tower noise reduction project is yet another example of the very poor diagnostic and engineering knowledge of many noise consultants. Far too often, decisions about noise control measures are made based on assumptions about noise sources rather than on accurate and precise diagnosis. There is a simple diagnostic process that must be followed when evaluating cooling tower noise control projects. This case study illustrates the power of simple, accurate diagnosis to remove all guesswork in solving noise problems quickly and at very low cost.

Detailed guide to selecting cooling tower noise attenuation techniques >

The noise from a 3m, 1.5MW wood-burning biomass boiler combustion ID fan installed at the Schiller power station in New Hampshire (one of the largest renewable energy projects in the U.S.) was dramatically reduced using innovative technology to replace the traditional silencer fitted to the power station fan. Our aerodynamic noise control technology not only cut the noise at source, but also substantially increased the fan efficiency.

The ID fan feeds a stack through a system that included a very large conventional silencer to prevent noise complaints from local residents. As this muffler had a drastic impact on fan efficiency, it had to be removed. This had a serious impact on the local environment, generating a host of complaints for which a very urgent solution was required.

Our aerodynamic source control technology was retrofitted instead of the attenuator within an incredibly short 12-hour downtime window. This not only eliminated the low-frequency tonal noise problem from this large industrial boiler system at a minute fraction of the cost of the silencer it had usurped, but as it also reduced the fan power consumption, the project was self-financing.

"The ID combustion fan created a low frequency tonal noise that could be heard on the other side of the river and was the cause of complaints. The installation process took only 12 hours, after which we recorded a huge 10dB drop in noise and measured a reduction in the power used by the ID fan.."  Jim Granger, Senior Engineer, Schiller

This international project was managed remotely from our UK offices. By analysing and interpreting data acquired locally to our specifications, we were able to dispense with site visits and reduce the entire process, from initial contact to problem solved, to a matter of a few weeks.

Filtration (bag filters etc) and conventional attenuators reduce fan efficiency by adding back pressure. We use Computational Fluid Dynamics (CFD) modeling and past experience to determine exactly where changes can be made to reduce back pressure and hence improve system efficiency. For example, it is often possible to modify existing silencers to reduce back pressure - or even to eliminate these attenuators altogether by using alternative techniques to cut broadband noise without the hit on fan efficiency associated with conventional noise control measures..

The approach not only reduces noise, but it also cuts running costs and increases productivity. This renders noise control projects of this type highly profitable so that implementing the modifications would be a valuable exercise, even if there was no noise issue...

As a result of complaints about noise from 2 large centrifugal fans on a factory roof and the involvement of the Environment Agency, the company spent £50k on traditional acoustic lagging that unfortunately had zero effect on the noise levels. This ineffective expenditure resulted in a prolonged wrangle with the authorities – who eventually suggested that they could get a 2nd opinion from us (based on our free analysis and diagnostic service).

They forwarded a video-clip and analysis of the sound-track proved that the problem was a pair of tones at the blade-pass frequencies of the 2 fans plus 1st harmonics that were interfering and “beating” with each other. We designed the solution in the form of aerodynamic Quiet Fan technology that provides retro-fit attenuation without using silencers. This eliminated the tones as a noise feature and the complaints ceased.

The whole process was completed within a few weeks at a tiny fraction of the cost of conventional alternatives. Moreover, only a single site visit was required – the rest of the work was carried out by email.

Highly tonal noise from these chillers had been the cause of complaint for some considerable time. The company had already attempted acoustic enclosure with the result that the chillers had over-heated.

The EHO sent us sound recordings, photographs and noise levels. Once analysed, we were able to say that the noise problem could be resolved for a few hundred pounds without running the risk of chiller problems. Once this information was passed on to the garage, they contacted us and we supplied them with detailed drawings that they used to get the silencers made locally.

Problem solved…

Analysis of the smartphone video sound-track shot outside the complainant’s house and close to potential noise sources on an industrial site allowed us to pin-down the source of the low frequency tone that had been the cause of long term complaints. Based on the mechanical information provided, we proved that the culprit was not the fan previously diagnosed locally, but a vibratory sieve. We then provided a virtually cost-free modification (mechanical disconnection from the building steelwork) to solve the problem. The whole process cost a few hundred pounds and only took a few days.

We have also generated a comprehensive technical note on all aspects of vibrating feeder, hopper, conveyor and screen noise...

A pair of air compressors installed in a plant room were generating noise levels well above the specified 80dB(A). We discussed the installation with the contractor, who then took some basic noise measurements plus photographs and smartphone recordings which were forwarded by email. As we have extensive experience of these types of compressor, we could use our noise control database as the basis for developing the solutions.

We designed retro-fit silencers and wall treatment, returned the recommendations and solved the problem by reducing the noise to well within the purchasing specification within a few days. The whole project cost less than a single site visit…

The manufacturer of hydraulic power packs for offshore use had to meet a very tight customer Buy Quiet noise purchasing specification. The unit had to include an acoustic enclosure within a very tight space for environmental reasons. In order to meet the requirements, we designed a combination of engineering control measures to reduce the power pack noise at source combined with an acoustic enclosure that included features to provide the required attenuation within significantly less space than a conventional soundproof box.

Hydraulic power pack noise sources and noise reduction features

The hydraulic power pack noise sources are listed below in rank order:-

1. hydraulic pump and associated vibration
2. oil cooler fan
3. pump motor, including fan

The noise from each source was reduced at source as far as practical to ensure that the dimensions of the acoustic enclosure were within the space constraints without compromising cooling. The following were the design features:-

• hydraulic power pack pump noise: control at source using high-efficiency damping
• oil cooler fan noise: geometric features coupled with compact, bespoke silencing to provide high attenuation without compromising cooling
• acoustic enclosure panels: included high-performance damping and tuned acoustic absorbent.

The detailed design was developed in conjunction with SoundDampedSteel who supplied both the highly damped laminated steel used and the enclosure itself to our specifications.

This project was carried out entirely remotely (no site visit) by email and smartphone using streamed pictures from site.

View detailed hydraulic power pack, pump and motor noise control guidance >