Industrial Noise & Vibration Centre

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Technical Notes - Environmental Noise

Environmental noise is fundamentally about the subjective impact of noise. However, there is typically a sad lack of accurate diagnosis relating noise features to noise sources and hence the recommended environmental noise control measures are all too often ineffective and costly. The following are detailed environmental noise control technical notes describing what constitutes "best practice" for each topic, including:-

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  • chiller fan
  • compressor

Chiller and Cooler noise control

Chiller unit noise control

Sound file: typical chiller low-frequency noise reduction,

The noise from chillers, air conditioning plant, condensing units, HVAC, heat exchangers, dry and adiabatic cooler AHUs etc provides a host of opportunities to waste resources on inappropriate noise control measures that either don't work or that reduce efficiency - or both. In our experience, a substantial proportion of the noise reduction measures used on these units (acoustic enclosures, silencers and barriers) are simply ineffective as they address the wrong problem.

There are only 3 types of noise generated by these systems: broadband air noise, compressor tones and low-frequency fan hum. The hum, for example, cannot be addressed using silencers and barriers, and yet these are often mistakenly fitted at high capital and running costs (reduced efficiency).

10 minutes with a smartphone is all it takes to avoid costly mistakes by determining which sources require treatment and what is the best noise control option for the particular problem. Anyone can do this.

This approach not only dramatically reduces typical noise reduction project costs, but it can even substantially improve system efficiency (by 23% on one data centre application). Find out how best to reduce the noise from chiller, condensing, cooler and related units here >

Data center noise control

data center chiller environmental noise reduction

Data center noise poses an increasing problem across the world as more and more are built to provide the digital services we all use. In addition, there are similar issues with crypto mining noise control. The 2 major noise sources on these types of site are the cooling systems (banks of fans on chillers) and standby generators. Whilst the latter are run to order for testing and are not usually much of a noise problem (as long as the low-frequency exhaust noise is properly attenuated), the former run 24/7.

Conventional data center noise control techniques such as acoustic louvres and barriers reduce cooling efficiency and increase running costs. Moreover, they cannot solve the very common low-frequency tonal hum complaint problems experienced by many sites.

However, there are innovative new low-cost techniques that not only cut noise, but also improve cooling efficiency thus making many noise control projects self-financing. As they also kill the low-frequency tones, they represent a seriously disruptive noise control technology that is often worth implementing for the efficiency gains alone, even if there is no noise issue.

In addition to cooling systems that run 24/7, there will also be power supply systems - either online (e.g. CHP turbines) or on standby (e.g. noisy diesel generator sets that are only run to a test schedule). As with cooling systems, low-frequency generator set tones may be a problem.

A data center noise control project that pays for itself is no longer an oxymoronic concept...

Find out how best to reduce data center and crypto mining noise here >

  • cooling tower

Cooling tower noise attenuation

Cooling tower noise reduction - gearbox

The key to effective cooling tower noise reduction is accurate diagnosis. Far too often, noise control measures are selected without a clear understanding of -

  • the type of noise problem: is it simply the overall dB(A) level or is there tonal character such as a low-frequency hum?
  • the source of the noise: fan (broadband or tonal); falling water; pumps (often tonal) and/or gearbox noise (tonal)

As a result, far too many noise control projects end in costly failure or go through a number of iterations before the problem is solved. Accurate diagnosis is not rocket science. Forward a few photographs and a smartphone video clip to us by email and we can provide a precise and accurate remote noise control diagnosis plus the optimum costed noise control options within an hour. At no cost.

There is also new low-cost aerodynamic technology that cuts the noise from cooling tower fans whilst often improving efficiency (unlike silencers and barriers that reduce efficiency).

Find out details of the best options to control the noise from cooling towers here >

  • dust
  • cyclone
  • fan noise control

Dust extract collector and cyclone separator noise attenuation

dust collector cyclone fan noise control

Conventional cyclone separator and dust extract collector noise attenuation measures are not only high-cost, but are often not very effective due to poor (or no) accurate diagnosis. This wastes resources and delays noise complaint resolution. Moreover, dust clogs conventional silencers, requiring regular maintenance or replacement.

There are simple, effective and low-cost control techniques to resolve cyclone separator and dust collector noise issues quickly and efficiently. The best option(s) can be selected by answering the following questions:-

  1. Are there tones e.g. a hum? Is it fans and/or resonances?
  2. Is the noise problem overall dB(A)? Is it air or material impact noise?
  3. Intermittent noise? Reverse jet filters?

If you are not sure of the answers to any of these questions, you can simply email us smartphone video clips and photos and we will get back to you with the options.

Find out about all the cyclone separator and dust collector noise control options here >

Diesel engine generator set noise

diesel generator set noise attenuation

Sound file: typical diesel generator set tonal noise

Diesel generator set noise often causes environmental noise problems in ways that are not necessarily obvious. The classic headline noise figures provided by suppliers of gen sets are usually expressed in terms of "XdB(A) at Y metres". This data can hide a multitude of hidden sins...

Take 2 generator sets with the same overall noise levels. One causes no noise problems. The other generates complaints over a wide area. The difference? The problem set is radiating low-frequency tonal noise from either the engine exhaust or the cooling fans that has little or no influence on the overall dB(A) as the "A" weighting attenuates low frequencies.

A simple diagnostic process using a smartphone is all that is required to avoid problems by diagnosing and ranking the gen set noise sources. The results can then be used to determine the optimum low-cost noise control techniques using the latest innovative technology, technology that can even improve cooling efficiency... Find out how best to reduce diesel engine noise >

How to outsource environmental industrial noise complaint problems

CHP generator set exhaust silencer

Environmental Health officers and Environment Agency staff (not to mention the companies with noise complaint issues) are making increasing use of our services to cut the time, resources and costs associated with the identification and resolution of industrial noise complaints. This simple process outsources most of the hassles and costs, providing: -

  • regulator costs: a dramatic cut in the required regulator staff project time and hence costs
  • complainant stress: typical industrial noise complaint resolution times are reduced from months or years to weeks, reducing unnecessary local resident stress
  • mitigation costs: a 50% - 90% cut in typical industrial noise generation mitigation project costs - a substantial benefit to the company involved

This win-win-win scenario is possible due to an innovative approach and technology that allows us to provide accurate diagnoses from smartphone data via email linked to the largest global database of best practice noise control solutions. This gives you access to a virtually instant Best Practicable Means cost/benefit analysis.

...frankly abysmal modern diagnostic and noise control expertise expressed in most consultant noise reports ...

It also provides a 2nd opinion as to the potential best practice alternatives to the frankly abysmal modern diagnostic and noise control expertise expressed in most consultant noise reports (independent surveys indicate that c 80% - 90% of noise reports are seriously inadequate).

Find out more about outsourcing industrial noise complaint problems...

Tonal noise (hum) evaluations. Why the abysmal failures?

All environmental noise control projects require 3 types of feature evaluation:-

stack and fan noise control
  1. Broadband noise (dB(A)): the simple default - quite often used inappropriately
  2. Low-frequency tonal noise that does not contribute significantly to the dB(A) value
  3. Intermittency/variability: impulsive sound, sources switching on and off

Despite tonal noise issues being very common causes of complaints, objective identification of the tones using narrow-band frequency analysis is incredibly rare in consultant reports. They present, at best, octaves and 1/3 octaves. Octaves are totally inadequate and 1/3 octaves are not much more useful. As there are very capable free smartphone narrow-band frequency analysis apps, there is simply no excuse for this lack.

This is rank incompetence that wastes time, money and resources

Including objective tonal analysis in assessments and environmental noise control reports is best practice. It not only accurately reflects the subjective effect of the noise, but it is also an invaluable diagnostic resource to determine the cause - and hence the optimum mitigation options.

How to use narrow-band analysis to evaluate and eliminate tonal noise problems >

  • noise control
  • noise analysis
  • environmental noise
  • EHO
  • environment agency
  • environmental vibration
  • remote control

EHO and EA - faster, simpler noise problem solving

noise in the environment

We provide extensive specialist technical support, information and training on noise and vibration to both regulators (Local Authorities (EHO) and Environment Agencies (EA)) and to industry. As we regularly deal with the same noise and vibration problems encountered, we have probably solved your problem already.

Our acclaimed range of EHO / EA specific noise workshops can help transfer time saving best practice techniques and technology in-house. This approach typically reduces the time to resolve noise complaint and other problems from months or years down to weeks - or even as little as days in some cases... This dramatically reduces the resources spent (freeing them up for other work) and also the time that local residents spend suffering unnecessary stress from unacceptable environmental noise.

We provide a worldwide service via the internet and smartphone technology. Make use of our Remote Control of noise service for a 2nd opinion and evaluation of best practice - or contact us for advice.

You can also outsource much of the time and resources required to resolve industrial noise complaints making the process much faster and more cost-effective.

Best Practicable Means / Best Available Technology evaluation service

Complaints and noise nuisance: how do you determine what constitutes “best practicable means” to mitigate. Companies employ consultants to generate reports claiming the cost of mitigation is too high to be practicable. In most cases, the suggested noise reduction technology is not best practice. Our definitions of low-cost BPM are game changers for regulators as problems can usually be resolved within weeks, saving time, resources and money.

We are quite happy to provide definitive definitions of what constitutes BPM/BAT with complete technical justifications, in court if necessary.

Noise and vibration training workshops

We provide very effective training for EHOs and Environment Agencies, from workshops to full CIEH environmental noise competency (some councils have profited from hosting in-house versions by inviting other authorities). These include:-

The Delegate View: “one of the most relevant and informative courses in a long time..” .. “I’d hate to come up against you in court! .. the best value seminar we’ve ever been on” – “standard of presentation was excellent .. humorous and entertaining .. highly recommended”

Our fan technology is saving megawatts per day

environmental noise control

As far as we know, the INVC is the only carbon negative noise consultancy in the world. We have achieved this by means of 2 major innovations...

Fan efficiency

Across the world, organisations using our aerodynamic fan noise control technology are currently saving megawatts of power as a result of the efficiency gains they have realised, compared with both conventional noise reduction technologies and in some cases, compared with unmodified fans. Our current record is a 22% improvement in the efficiency of cooling fans as part of a noise control project.

Remote noise control - hold the site visits...

We have developed technology that allows us to complete an increasing proportion of our noise control projects anywhere on the planet without a site visit. This not only reduces our carbon footprint (flights and other transport costs etc), but it is also faster and lower cost.

Our remote control of noise services uses email and remote working (e.g. Whatsapp) to carry out diagnoses and the development of best practice noise control solutions. We also use innovative technologies to avoid traditional resource-heavy noise control measures such as barriers and acoustic enclosures in favour of elegant engineering that helps clients to reduce their carbon footprints.

E-analysis: noise diagnosis and control by email

71Hz 75Hz environmental noise tone identification

Environment Agencies (EAs), environmental health (EHOs), noise consultants and organisations in many countries regularly use our free online noise diagnosis and control best practice service to eliminate time-consuming hassles. All you need to access unique expertise and technology that reduces time and resources spent on projects by an order of magnitude is a smartphone on-site.

E-analysis: this approach not only cuts typical noise project investigation and resolution time from months or years down to a few weeks - or even a matter of days (our current record is 2 days from initial contact to noise control implemented and problem solved), it also reduces noise control costs by 50% - 80%.

wapp logo.png

You can take a "virtual noise expert" to site anywhere via Whatsapp "telepresence" to provide instant feedback and analysis.

E.g. for a suspected chiller noise problem: "Record now at the site boundary, then move close to the plant and record again. Ok, there are 2 series of tones. Check the fan speed and take a close-up. Ok, the low-frequency tone is fan blade pass and the higher frequency tones are from the compressor. The former would be an £800 fix that would improve efficiency and the latter around £1k."

Regulators and consultants routinely send smartphone data from site visits for a free expert opinion. We can usually provide source identification and costed noise control options based on current best practice within 1 or 2 days.

Get more detailed information and case studies about the remote noise analysis and control options >

  • chiller fan
  • compressor

Efficient heat pump noise reduction options

air source heat pump noise control diagnosis

The noise from heat pumps, be they air-source or ground-source units, often poses a serious problem as not only can they be loud, but they are also installed very close to or on noise-sensitive premises.

The result: noise complaints

Unfortunately, current heat pump noise specifications and limits are often inadequate as they do not take into account the common low-frequency tonal nature of the noise generated by many heat pumps.

Ineffective heat pump noise control is far too common...

Mis- (or no) diagnosis of the characteristics of heat pump noise is extremely common, leading to money wasted on noise control measures that are either ineffective or that reduce efficiency - or both. Our experience indicates that a substantial proportion of the noise mitigation measures applied to these units (acoustic enclosures, attenuators, barriers) are either over-engineered or ineffective as they address the wrong problem. This is supported by the fact that the Environment Agency and EHO surveys indicate that 95% of noise reports are inadequate.

There are 2 categories of noise generated by heat pumps:

  • broadband noise - mid-high frequency noise that controls the overall dB(A)
  • low-frequency tonal noise e.g. fan or compressor/pump hum

The latter cannot be addressed using the silencers and barriers so often installed due to simple physics. Moreover, these can reduce system efficiency.

A few minutes with a smartphone is all that is required to carry out the proper diagnosis to determine and rank the noise sources and hence to the optimum noise control options. Anyone can do this.

This approach dramatically reduces the costs of typical noise reduction projects and can even simultaneously improve system efficiency.

Find out how best to reduce heat pump noise here >

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