An examination of the structural factors to take into account in order to tackle HVAC-related noise pollution in industrial facilities.
Industrial HVAC systems play an instrumental part to provide heating, cooling and ventilation to a wide range of facilities such as chemical processing plants, manufacturing facilities, power generation plants and water treatment plants.
They are normally larger and more complex than residential HVAC systems, which makes them also statistically at higher risk of becoming noisy spot.
As a matter of fact, these installations are inclined to produce loud sounds at the damage of the surroundings. It is therefore clear that all the facilities hosting these machines should need to adopt, willy-nilly, a soundproofing strategy in case the hearing comfort of the operating individuals is put in jeopardy.
The initial step of the approach implies the determination of the area where the HVAC systems is installed. Being placed outdoor means, for instance, be arranged for a specific solution over another.
Moreover, as anyone would expect, the location of the HVAC device determines the type of the HVAC equipment. For instance, components such as chillers, fans, cooling towers, and pumps fall within the outdoor HVAC equipment. On the other hand, components such as ducts, junctions, diffusers, and cooling coils are likely to be found inside facilities.
HVAC-related noise control can be engineered by employing two distinct classes of materials: absorptive ones, which naturally absorb sounds, reduce reflections from surfaces and decrease reverberation within spaces, and sound partitions or barriers, which reduce sound transmission between adjacent spaces through non-porous textures, generally recognized as good reflectors of sound.
Reducing noise transmission from outdoor machines requires, firstly, an accurate mapping processof noise propagation. Ventilation of buildings, enclosures and equipment rooms should be meticolously evaluated. Structural factors should be already considered when selecting HVAC equipment and while designing air distribution systems to minimize the noise. The overall design requires, a careful assessment of all the limitations of space, selection of fan, and aerodynamic pressure drops. The final objective is to eradicate the noise created by the flow of air or gas while simultaneously maintaining the flow itself and keeping the pressure drop minimal.
Three main cutting-edge soundproofing technologies provided by Stopson Italiana are suitable to HVAC systems: Acoustic Louvers, Intake Silencers and Acoustic Enclosures. These are indeed durable and easy-to-operate solutions to be integrated as noise control measures into the system design. A series of Silencers specifically designed for HVAC are a perfect fit for applications requiring maximum insertion loss (noise reduction), low static pressure drop, low maintenance, and quick delivery. They can be incorporated into the ventilation system and paired with the machine to fully soundproof it towards all directions.
Explore our news about Industrial Silencer applied to HVAC system to deep dive into the topic.
In our first article devoted to the topic, we have introduced the theme of the current shift towards the integration of green, sustainable, and advanced materials that might produce some future applications in the soundproofing global backdrop.
Strengthened by new research, data, and insights, we continue to bring about an in-depth analysis over the transitional phenomena by showcasing some further solutions that have been studied and proposed throughout some of the latest academic contributions.
The purpose of these experimental investigations was to explore the Sound Absorption and Attenuation potential of products and architectures employing alternative materials, which have been already proved to be a valid substitute to traditional solutions.
1. Sound-absorbing Boards made of maize stem
Ramshankar et. al (2021) have developed a research project that studied soundproofing board made from maize stem. This can already be regarded as a beneficial component in those industries where the need to overcome serious noise pollution is regularly encountered, since these structural elements could significantly give a support to eradicate harmful sounds and so reproduce a better working enviroment as well.
The study lies also on the assumption that many of the soundproofing solutions currently available in the market are not so cost-effective. The usage of soundproofing panels based on agro-waste can represent a better solution in such terms too.
Basing their empirical methodology on the Impendance Test, Ramshankar et. al (2021) have drawn the conclusion that, as for maize stalk, the thickness has a very irrelevant influence if we compare it with other natural fibers. At the same time, by comparing different sound absorption co-efficients, it has been observed that maize stalk performs better than several other materials.
However, the most precious insight is that agro-waste panels does not cause any damage to environment, and, additionally, cost of production are also very restricted when compared with other products. Overall, maize stalk as a soundproofing solution succeeds in achieving three main lenses in a all-in-one: cost-efficiency, sustainability, performance.
2. Metamaterials with an eye to naval soundproofing
Metamaterials are made-from-scratch solutions that reach electromagnetic properties which are not normally part of natural elements. D’amore et. al (2022) have investigated a “metasolution” – as it was called in the study – having the potential to replace traditionally adopted solutions especially regarding marine applications. Noise attenuation techniques intended to soundproof marine and naval equipment are indeed becoming an essential asset to ensure the comfort levels required by the standards on board ships.
As highlighted by D’amore et. al (2022), acoustic metamaterials “are engineered to control, direct, and manipulate sound waves, by transmitting, trapping, and amplifying the sound waves at certain frequencies. This outcome is usually achieved by the periodic repetition in space of an elementary primitive cell, carefully optimized in its topology and geometry”.
Panels made of metamaterials have suitable features, sufficient to be a valid sustainable solution on board ships, especially as an alternative to traditional mineral wool products. This type of solution could pave the way for the slow but unavoidable substitution of traditional solutions for vibration and noise control in other configurations in marine soundproofing.
Stopson Italiana is further growing its awareness of the environmental impact caused by conventional methodologies. It is noted how research and academic studies are largely contributing to powering the transition towards Sustainable Materials byoffering plenty of insights.
It is demonstrated that Advanced and Eco-friendly Materials are already an indispensable resource with a view to better manage not only the complexities of soundproofing execution, but also to make the industry more outcome-centric due to their profitability. Technicians and surface specialist are therefore expected to embrace this knowledge and exploit the opportunities offered by the newest solutions.
As it is occurring in many other industries, the soundproofing global ecosystem is witnessing a shift towards biodegradable materials. Manufacturers are expected to integrate green and sustainable materials with traditional ones while designing their industrial noise control units. It is in fact necessary to bring into line with the ongoing sustainability trends and those requirements set out according to the needs of the present time.
Yet, for a long time now researchers had discovered that natural materials can be effectively used in the construction of sound absorbing architectures with a view to erase noise pollution inside facilities.
However, apart from being required to protect the environmental quality overall, it seems that natural materials can be as effective as conventional solutions.
Preferred Materials: current scenario
As stated by a recent FMI’s study on the state of health of the soundproofing global market polymers and composites still remain the highly preferred materials for the manufacturing of sound proofers. Polymers and composite materials are acknowledged to have higher soundproofing properties as compared to other materials such as glass, metal, and fabric.
Anyhow, the recent developments in composite materials have provided them with the assets of biodegradability and recyclability, which has automatically led to higher sales too. The study estimates that in 2018 alone over 4 out of 10 industrial noise control units made of polymer amd composites have been sold.
Green and Eco-friendly industrial materials
The acoustical natural solutions are still turning more and more into a valid alternative to traditional synthetic applications, as there is much higher effort in developing sustainable absorbers, either from biomass or recycled materials.
In 2021, AcouTech Lab in Tallinn University of Technology delineated a underlying premise: in order to express the noise attenuation potential and achieve the best results in terms of performance, the absorbers’ design should be based on materials with open pores structure, the pores should have small size, and the core material should have high elasticity, while the thickness of the material should be large enough to offer a reasonable attenuation at lower frequencies.
As for conventional materials, absorbers’ performance largely depends on their fibers and structure of pores as well. Cotton fibers have as many noise absorption properties as rock wool and fiberglass do, which are usually employed to realize conventional absorbers. Cotton’s porosity allows it to receive and then contain the sound energy with ease, and plus makes the material compactable, so that designers can form it into thick sheets that ensnare and disperse sound.
Against the current backdrop, soundproofing companies should employ cotton-based materials while developing their products, especially with an eye to reduce echoes and reverberations.
There is a concrete opportunity to launch green product lines including sound proofers such as wall and acoustic panels,baffles and HVAC acoustic liners mostly made from recycled cotton or recycled synthetic fibers.
How and what you need to know to soundproof properly your plant
Some basics about noise
Noise is commonly defined as unwanted sound. A typical noise control problem includes three basic components: the noise source (machines, fans, pumps, processes etc.), the receiver (persons subjected to the noise); and the path (the route the noise travels between the source and the receiver indoors or outdoors).
Noise can be classified in two different forms: airborne and structure-borne.
The first one goes from a source to a receiver as a differential in atmospheric pressure, traveling in all directions. Structure-borne instead is unwanted vibration, which is transmitted from a vibrating source to a receiver through a solid material and regenerated as airborne noise. Once the three main elements (source, path and receiver) have been identified, four ways can be adopted to control the noise: absorption, barriers (blocking), damping and vibration isolation.
Perhaps the greatest single contribution of unnecessary noise is the lack of proper maintenance and corresponding preventive maintenance intervals. Equipment that is poorly maintained eventually becomes inefficient. One manifestation of inefficiency is noise (misdirected energy), which, ultimately, becomes the subject of replacement. Typical energy wasters and noise producers are:
Improperly aligned belts
Unbalanced rotating parts
Reciprocating striking parts
Insufficiently lubricated parts
Contact between moving and stationary parts
Compressed air leaks
Vibrating sheet metal, such as streamlining
Improperly adjusted linkages or cams
How to choose the most appropriate Steam Vent Silencer provider
Which are the most relevant data to be considered in order to identify the correct roles within the supply chain of acoustic manufacturers. Understanding all of the factors involved could simplify the selection of the rightest vent silencer for the application required. But first, it’s important to introduce vent and blowdown silencers, reviewing the factors involved in predicting the noise generated by high-pressure vents.
Here below a list about the blowdown and vent applications that require silencers:
Steam venting in power generation applications
Process control and relief valves in industrial applications
Pipeline blowdowns and Natural Gas compressor station
Blowdown tanks and autoclaves
Bypass valves on blowers and compressors
Discharge of high-pressure gas to substantially lower pressure environment (atmosphere).
Steam ejectors and hogging vents
Vent Silencers and their applications
The terms “vent silencer” and “blowdown silencer” refer to the relative application for which each one is used. For both of them the design is similar, since we refer to vent silencers when being used to vent at a constant flow rate, for a period of time. The word silencer is instead referred to as blowdown, when they are blowing down a finite volume of gas starting at a high pressure, and ending at a low pressure over a given time. Vent silencers are sized for constant flow and blowdown silencers are sized for maximum flow.
Vent silencers find wide applications in high pressure vents, steam vents, safety relief valve outlets, system blow downs and purge outlets etc. Vent and blowdown noise is a function of upstream pressure and temperature, type of gas being vented, the valve size and type, plus the effect of downstream piping.
Stopson Italiana designs and manufactures high quality Vent Silencers that attenuate the high noise produced by the expansion of Gas, Steam or Air at elevated temperatures to atmospheric pressure.
When it’s required the installation of a Vent Silencer, here below all the data required in order to obtain a precise offer:
Application (Vent, Blow down, Relief)
Fluid Composition (Steam, Gas, Air)
Molecular Weight or Specific Gravity
Process conditions upstream of valve and units (lb/hr, SCFM, ACFM)
Temperature Pressure (P1)
Atmospheric pressure ( Pa ) / Temperature (T2)
Line size between valve and silencer
Line size from silencer discharge
Attenuation required (silencer performance)
Allowable pressure drop
Noise Generated by High-Pressure Vents
Over the years, there has been a good deal of work done in the field of predicting the noise generated by the high-pressure venting of gases.
Factors Influencing Noise Generated by High-Pressure Vents:
Mass flow – the higher the mass flow, the noisier it becomes.
The type of gas and its molecular weight/specific gravity – lighter gases are noisier.
Temperature – higher temperatures result in lighter gas flows, and therefore, higher noise levels.
Upstream versus downstream pressure – the higher the upstream pressure is relative to downstream pressure, the louder it will be.
Choke flow (critical flow or sonic flow) – occurs when upstream pressure is roughly two times or greater than downstream pressure, making things much noisier.
Orifice/opening size of valves, vents, orifice plates, diffusers, etc. – larger diameters result in low frequency noise, while smaller diameters produce higher frequency noise. For instance, diffusers create a shift in the noise spectrum from low frequency (one large vent opening) to high frequency (many smaller openings), which is much easier to attenuate.
Elements Creating Noise in High-Pressure Venting Systems
The noise at the end of a high-pressure vent pipe is a combination of the noise generated by the high-pressure-drop elements in the system. Essentially, any element that has a high-pressure drop across it or large change in area will create noise and should be included in the noise model to accurately predict overall noise level.
The major elements that create noise in high-pressure venting systems are:
Pressure relief and control values – present in virtually all venting systems.
Vent pipes/nozzles – last element in venting systems, except for those using high-pressure silencer diffusers.
High-pressure silencer diffusers – when included, usually designed to provide a specific backpressure at the rated flow (sometimes used as fail-safe device).
Orifice plates – included in many systems as a flow regulator or fail-safe device.
Enlargers (reducers), headers and abrupt transitions – included in pipe systems for various reasons. Shock Noise Versus Turbulent Mixing.
There are two phenomena that produce noise in a high-pressure venting system:
Shock noise – occurs when a choked flow condition exists
Turbulent mixing – caused by the ripping of the air as the vent gas decelerates to lower velocity, such as the atmosphere. Shock noise is the louder of the two. By adjusting the elements in a piping system it is possible to reduce the shock noise by reducing the magnitude or quantity of choked flow conditions present. Turbulent mixing, on the other hand, is always present, though less of an issue.
Industrial silencers: an increase of demand due to a more strict regulation for industries
An integral part of today’s industrial process and ventilation systems, industrial fans, blowers, and compressors are leading causes of noise problems. If unaddressed, these issues can lead to health and safety concerns, as well as environmental regulation violation. With the tightening of noise regulations, industrial facilities are required to stay in compliance with regulations. Industrial silencers are typical being used to attenuate noise coming from intake and exhaust systems of industrial facilities. These silencers may be built in limited space. Inside an industrial area, fan installation is one of the most predominant source.
Industrial silencers are engineered to control noise in specific applications, and can alleviate problems in work facilities. With more than 50 years of experience Stopson Italiana soundproofed plants in a broad range of installations, such as:
Gas Turbine Engine Exhaust Silencers
Silencers are required for almost all installations that particularly include gas turbines and heat recovery steam generators. Our Gas Turbine Exhaust Silencers are especially designed to work in an environment where they are simultaneously exposed to high temperatures and to high velocity turbulent flow.
Stopson Italiana provides full custom engineered Inlet Exhaust Silencers for Gas Turbines, DG sets Turbo Compressors and Turbo Blowers. They entail complete solutions in the field of Machinery filtration and acoustic solutions for Gas turbines and compressors.
Stopson Italiana Gas Turbine Silencers provide the ideal solution to keep noise at a manageable level, while maintaining the operating efficiency of your turbine intake system.
Stopson Italiana designs and manufactures all types of discharge silencers in compliance with the international quality standards. Our discharge silencers are very much effective in reducing the noise for entire systems that receives air for heavy engines & turbine.
Stopson Italiana engineers have been designing application-specific products and services for industrial plants and processes since 1965. Each product manufactured is tested and inspected to meet all applicable industry standards in terms of quality, longevity and safety.