Noise reduction for HVAC and industrial systems - Blog

Noise reduction of large heat pumps and large refrigeration systems.

Sat, 07 Mar 2026 18:16:16 GMT

We are receiving more inquiries about the noise reduction of air-cooled large-scale heat and large-scale refrigeration systems with a single output > 200 kW, which require a reduction in noise emissions of 25 dB(A) and more in order to comply with the legal noise limits. In many cases, multiple systems are planned in this performance range on a small area.

The dilemma of installation often arises during the planning phase. Real estate investors do not want to free up space for the investments that can be rented out. As a result, planners are often forced to plan the systems close to the property boundary on roofs, etc., and then quickly encounter the quiet needs of the adjacent residents.

Since the noise emissions of air-cooled systems cover an emission spectrum of 32 to 8K Hz, these noise reduction requests quickly come up against the limits of physics, or rather the sound insulation and sound absorption limits of the materials available today. Further on available areas to be able to build sound enclosures with the envelope necessary for noise reduction.

One difficulty is the high air volumes that these plants require at full capacity, which are usually > 150000 m3/h to call up the full plant capacity. In addition, there are usually multiple compressors that are switched on depending on the power level. Individual scroll compressors in the 400–600 kW range are typically around 80–86 dB(A) Lw in the "Low noise" version, while SuperLowNoise variants achieve a further reduction of around 3–5 dB(A). Noise from the hydraulics and intake noises due to pressure losses on the evaporator side are of course added. In practice, the distance between 1/4 and 4/4 speed can be larger because higher fan speeds are usually driven at full load, this is especially true for refrigeration systems. In heat pump operation, the fan speeds are not significantly reduced even in partial load operation.

The dilemma now when planning sound enclosures for large heat pumps is to create enough free space for air circulation and to keep the air velocity and pressure losses through the sound enclosure as low as possible. In practice, this means that with an air volume of 150000 m3/h, we need 6.9 m2 of free space to increase the air velocity to 6 meters/sec. and the pressure loss to 24 Pa. and prevent air flow noise.

In limited areas, which is the case in most projects, this means designing the air duct in such a way that noise-critical areas in the vicinity are not directly in the escaping sound of the system. This means that the free air intake areas must now be accommodated on a reduced perimeter without generating direct air vortices.

Since the fans also discharge low-frequency sounds in the range of 32 to 250 Hz, there is still the problem of reducing this sound at the source. Especially in this area, most of the materials available on the market today usually have a very low effect.

Full of hope, I have therefore dealt intensively with acoustic meta-materials in the last few months and have come to the realization that most manufacturers mainly address the frequency spectrum of 250 to 500 Hz and are largely still in the development phase and have hardly any available products.

In the frequency range from 32 to 250 Hz airborne sound, resonant acoustic meta-mmaterials (membrane and Helmholtz type) are particularly effective, which can be specifically tuned to this range. However, a lot of development is still needed here to develop effective products for the masses. However, I am convinced that metamaterials expand the "design space" within existing physics, but they do not create perpetual motion effects, no true hyperlight communication and no violation of conservation or causality principles.
Of course, a few additional dB can be reduced with specifically tuned resonators and/or meta-material panels in the range of 32 to 250 Hz, but the whole thing remains a physical challenge (wavelengths, a lot of leakage potential through the free ventilation openings). Fan reserves, defrosting behavior and recooling temperatures must also be coordinated with the hood geometry and gate resonator arrangement.
In the meantime, the choice of installation locations as far away as possible from noise-critical locations is still the ideal solution and helps in the planning of sound measures, taking into account their performance and the possibility of protecting critical areas from noise emissions through targeted air ducting.

Forcotech Air-Routing Large Heat Pumps und Chillers

Acoustic Meta materials for the Reduction of Noise Emissions from HVAC Systems

Mon, 09 Feb 2026 07:57:45 GMT

Acoustic metamaterials are specially structured materials that can block or absorb sound in certain frequency ranges in a very targeted manner and can therefore also be interesting for the sound insulation of heat pumps and refrigeration systems.

What are acoustic meta-materials?

Meta materials are not new substances, but conventional materials (e.g. plastics, metals, glass) that acquire new acoustic properties through a micro or macro structure.
In acoustics, many small resonators (diaphragms, mass-spring systems, cavities) are often arranged periodically; this creates so-called stop bands, i.e. frequency ranges in which sound hardly propagates. A principle on which Helmholtz resonators are already based. Such structures can, for example, reduce sound in the range between 500 and 1K Hz by up to 20 dB through a baffle without the wall becoming thick or heavy.
Classic sound insulation usually works with mass (heavy walls) and porous absorbers; Meta materials, on the other hand, use targeted resonances and interference effects to strongly attenuate certain frequencies.
In Vibro acoustic metamaterials, mechanical resonators are integrated on or into a support structure; they absorb energy from the vibration in the exact frequency range for which they are tuned, thus reducing structural and airborne sound. There are passive variants (structure only) and active variants with sensors and actuators, in which the stop bands can even be moved during operation to adapt to changing noise spectrum's.

Relevant frequencies for heat pumps

Air-to-water heat pumps mainly generate noise from the fan, compressor and flow noise (air/refrigerant), often in the range of 32 to 8KHz. In my opinion, meta-materials are promising here to suppress exactly the dominant sound and tape noises (e.g. fan fundamental frequency and compressor frequencies) more efficiently without making baffles or sound enclosures very heavy or thick.

Possible applications for sound enclosures for heat pumps and refrigeration systems

Sound barriers are conceivable in which the wall panels are equipped with resonator arrays made of plastic or metal on the inside, similar to vibro-acoustically optimized foundations.
As with noise barriers, existing enclosures or walls could also be upgraded to "meta-walls" by glued or screwed on resonator modules without changing the base material. For example, walls around facilities or other obstacles could also be equipped with meta-materials to prevent the reflection of sound.

State of the art and practical relevance

Vibro Acoustic meta materials have already been prototype in noise protection (e.g. Fraunhofer ISE and IBP) and show significantly better reductions in the laboratory than simply doubling the wall thickness.

For heat pumps, classic soundproofing hoods and baffles with porous absorbers and air deflections through Louvre or Labyrinth systems are currently commercially available and achieve a reduction of 15–22 dB(A) over the frequency spectrum. The frequency range of < 63 Hz is not addressed by most products today, in-situ measurements show that in the range of 32 Hz with sound obstructions, a higher sound emission can also result.
Meta material-based solutions for heat pumps are currently still in the development stage, but should become interesting in the medium term when lighter, specifically frequency-tuned hoods with better damping are required, that these requirements will come is already foreseeable today due to the spread of heat pumps and air conditioning systems, who can then specifically reduce the insulation in certain sound emissions critical frequencies will be able to secure a leading market position.

Romolo Vicari 09.02.2026

Increasing the surface area of STRATOCELL®WHISPER® FR panels

Thu, 08 Jan 2026 13:15:01 GMT

The surface of STRATOCELL® WHISPER® FR panels, which we use as internal insulation of sound hoods for HVAC systems, were modified in a trial for optimized sound absorption and equipped with additionally punched and attached round Whisper molded parts. The punch hole served as an additional air cushion.

The die-cut and applied STRATOCELL® WHISPER® molded parts further improve the overall absorption of Whisper panels by increasing effective sound wave penetration and surface roughness. We used round WHISPER moulded parts with a diameter of 5 cm and a depth of 5.5 cm, which were punched directly from the panels.
These modifications improve sound absorption in the mid- and high-frequency ranges, as they allow for more angles of incidence for sound and promote resonances. The total NRC (Noise Reduction Coefficient) values of the panels increase by 10-20% according to our measurements, depending on hole diameter, depth and degree of coverage.
Absorption EffectsThe perforated or round punched parts increase absorption by directing sound waves into the porous polyethylene structure, which minimizes reflections. The attached elements act like diffusers that scatter sound waves to reduce echoes without significantly reducing the self-sustaining capacity of the panels.

Romolo Vicari / 08.01.2025

Underwater sound propagation from offshore wind farms, oil rigs, underwater data centers, etc.

Wed, 07 Jan 2026 19:04:26 GMT

Sound travels much faster and farther in water than in the air, as water is a denser medium. The speed of sound is typically around 1480 m/s in the ocean, depending on temperature, salinity and pressure, compared to air where the speed of sound is 340 m/s (reference 20° degrees outside temperature with a relative humidity of 50%).

Offshore wind farms, offshore drilling platforms and now also the construction of underwater data centers generate underwater noise, especially during construction by driving foundation piles, as well as during operation by vibrations of the turbines.

The following sound sources are to be distinguished
Construction phase:
Pile driving work generates impulsive peak levels of up to 250 dB, which can be heard for miles.

Operation:
Continuous noise from gearboxes, generators with levels around 100-160 dB at a distance of 100 m.

High sound levels disturb marine fauna and lead to hearing damage, stress, injury or even death, for example in porpoises, whose biosonar is disturbed. Fish such as cod suffer masking effects that hinder foraging and flight, as well as population weakening. Around 150 species are affected, including krill, whales and dolphins, with consequences such as reduced reproduction and immune deficiency.

Sound-reducing techniques
significantly reduce underwater noise during the construction of offshore wind farms, they can greatly reduce noise levels and minimise area dispersion, which is significantly higher in the water than in the air.

Bubble Curtains:
Perforated hoses form air bubble rings around the ramming point that refract sound waves, while double variants such as Big Bubble Curtain achieve reductions of 18 dB.

Cofferdams:
Temporary housings around the pile that insulate sound, often combined with bubble curtains.

Hydro Sound Damper (HSD):
Air-filled balloons or foam elements in nets, adaptable to frequencies.

Alternative foundation methods
Drilling techniques, suction buckets or floating foundations completely avoid pile driving and generate less noise. Soft-start methods slowly increase hammer energy, supplemented by deterrence systems such as Pingers to displace the animals in the area.

Influence of temperature and humidity on the propagation of airborne sound in the atmosphere

Tue, 06 Jan 2026 18:48:50 GMT

Airborne sound is attenuated as it propagates in the atmosphere depending on frequency, temperature and humidity; this is particularly relevant at medium and high frequencies and large distances between the sound source and the receiving location. With increasing temperature and medium to high humidity, both the speed of sound and the strength of absorption change significantly. Airborne sound absorption is the conversion of sound energy into heat through molecular friction and relaxation processes of the air components.The atmospheric absorption coefficient is usually given in dB per 100 m and increases sharply with frequency; low frequencies are much less attenuated than high frequencies.

Influence of temperature
The speed of sound in the air increases with temperature and is at 0 °C at about 331 m/s, at 20 °C at about 343 m/s and at 35°C at 352 m/s

. With increasing temperature, the relaxation processes of the air gases shift, which changes the frequency-dependent absorption; at high frequencies, the air attenuation can increase significantly with temperature.

Influence of humidity
Humidity changes the composition and relaxation properties of the air, which changes the atmospheric absorption coefficient as a function of frequency and relative humidity.
For many frequencies above about 1 kHz, the absorption initially increases with increasing relative humidity up to the range of 20% and then decreases again at even higher humidity. Very dry as well as very humid air therefore attenuate high-pitched sounds to varying degrees.

Practical significance
In normal indoor spaces, material and surface absorption dominate. Air absorption only becomes relevant in large rooms or outdoors at distances of tens to hundreds of meters. Particularly in the case of traffic noise, aircraft noise, noise from industrial plants or sound reinforcement over long distances, temperature and humidity profiles must be taken into account in measurements because they can noticeably reduce the levels of high frequencies at the receiving location.

Calculation / Standards
For technical calculations of air absorption, the ISO 96131 standard is often used, which indicates the atmospheric absorption coefficient as a function of temperature, relative humidity and frequency. The standard takes into account frequencies from 50 Hz - 10 kHz), temperatures from -20°C - +50°C, a relative humidity of 10% - 100%) and air pressure.

Forcotech Schallschutz - Schallausbreitung in der Atmosphäre

Impact of Layer structure in sound insulation

Sun, 26 Oct 2025 12:08:03 GMT

The combination of StratocellWhisper, heavy foil and an additional air cushion results in a particularly high-performance multi-layer system for sound and vibration insulation. This principle uses an extended form of the mass-spring-mass system, which effectively reduces both airborne and structure-borne noise.

Construction principle: mass-spring-mass:
The heavy foil forms the outer "mass" and blocks airborne noise due to its high surface mass.
The Stratocell Whisper acts as a "spring", absorbing sound energy and decoupling mechanical vibrations.
The air cushion reinforces this decoupling as it represents an acoustic resonance layer that attenuates particularly low-frequency waves.

Exemplary layer structure:
Base (sound-repellent side): Heavy foil 3–5 mm, mass weight ≥ 5 kg/m²
Air gap (30–50 mm, double if necessary): acts as a resonant buffer
Stratocell Whisper (40–60 mm): absorbs sound and suppressesreflections.

This combination creates an extended range of attenuation:
The air gap lowers the resonance frequency of the system.
The heavy foil prevents sound transmission.
Stratocell Whisper absorbs medium and high frequencies.
Together, all layers can achieve a reduction of over 30 dB, depending on the structure and frequency range.

Technical notes:
A 50 mm air gap behind Stratocell Whisperdrastically increases absorption at low frequencies and can lead up to absorption class A (NRC ≈ 1.0). If a second cavity is added (e.g. a double layer of air),the sound path lengthens and the acoustic impedance improves again.

Application:
This construction is particularly used in areas with a low and broadband sound spectrum:
Soundproofing enclosures for HVAC systems, transformers, BESS systems, and combined heat and power plants
Machine enclosures and enclosures in industrial environments. Acoustic walls and partition systems with requirements for high building acoustic performance.

Result:
The additional integration of an air cushion between the heavy-duty film and Stratocell Whisper creates an extremely efficient, broadband soundproofing structure – ideal for applications where there are high requirements for sound insulation combined with effective sound absorption.

HVAC acoustic hoods Design from concept to recycling

Sun, 19 Oct 2025 17:31:56 GMT

Our acoustic enclosures for heat pumps, air conditioning and refrigeration systems are made entirely of aluminum, with a base frame made of an aluminum plug-in frame with a bolted connection. Individual modules can be combined to be able to enclose larger systems without the installation on the construction site becoming a problem.

In the case of rental systems, there is also the advantage that after the rental period, the sound hoods can be dismantled without much effort to reuse them in other projects and systems.

In addition, our sound hoods and sound barriers, like all products, are subject to a life cycle, which is why we take into account the factor of dismantling and recycling as early as the design stage. Our design principles, which facilitate subsequent disassembly, include, above all:

Using detachable or reversible joining techniques such as screws, rivets, clips instead of adhesives or welding, so that components can be easily separated. In this way, we prevent permanent connections and connections that are difficult to dissolve mechanically or thermally.

Even the internal insulation is not glued but mechanically secured, so that it can be removed at any time with a flick of the wrist.

In addition, we reduce the variety of materials to a few single-type materials or mono-materials to enable single-type recycling and facilitate separation. In the production of aluminum panels, the offcuts are consistently used to produce other parts such as mechanical, static fuses and covers. In this way, we prevent the mixing of different alloys, which leads to a downsizing of the material quality during aluminum recycling.

The design also considers the easy accessibility of all connections and components, e.g. through standardized screws and accesses and corresponding clearances.

Use of environmentally friendly, recyclable materials and coatings that do not hinder recycling.

Construction of a soundproof enclosure for 10 solar inverters.

Fri, 15 Aug 2025 18:29:47 GMT

In a PV field directly adjacent to a residential area, the operation of the inverters caused noise complaints from residents, especially during the summer months.

The dominant sound frequencies of photovoltaic (PV) inverters can be divided into two main ranges:

Medium to high frequencies (approx. 200 Hz to 5000 Hz): This range is dominated by fan noise, which is used to cool the inverter.

Very high frequencies (approx. 4 kHz to 200 kHz): These frequencies are generated by the internal switching processes of the inverter, by pulse width modulation (PWM) during frequency and voltage conversion. These high-frequency sounds can be perceived as particularly unpleasant, beeping noises.

The total sound power of inverters is often in the range of 65 to 84 dB(A).
In addition, the reflections of sound from nearby walls cause the noise to spread to more distant areas, which can impair living comfort.

One technical problem is that increasing the switching frequency to shift the sound emissions into the barely audible range has a negative impact on the efficiency of the inverter and greatly increases its cooling requirements.

The sound enclosure for the 10 inverters has the following dimensions: 11000 x 1800 x 2900 mm (L x W x H). The interior insulation of the enclosure consists of 40 mm thermal insulation and 40 mm sound insulation (StratocellWhisper) on top.

All structures for mounting the inverters and routing the cables are also installed in the enclosure.
Openings on the underside of the sound enclosure and in the upper area allow fresh air to be supplied and warm air generated by the operation of the inverters to be removed.

Although the sound enclosure with RAL-7016 does not have the ideal exterior color to minimize heating from solar radiation, the interior temperature in the enclosure remains around 5 degrees below the ambient temperature thanks to the combination of thermal and sound insulation. This means that the use of the sound hood also prevents temperature-dependent derating, which serves to protect sensitive semiconductor components of the inverter from overheating and causes the inverter to shift its operating point to a lower power level.

From an acoustic point of view, it is interesting to note that noise emissions are assessed by the authorities as a total sound level, which significantly reduces the sound reduction requirements as the sound sources are not added together.

From a practical point of view, this is nonsense, as the inverters never run in exactly the same operating mode at the same time, so the sound levels should actually be added together (unequal sound source).

acoustic enclosures connecing to lightning protection.

Mon, 21 Jul 2025 15:08:57 GMT

Acoustic enclosures for heat pumps, air conditioning, and refrigeration systems can be ideally integrated into a variety of environments thanks to the free choice of exterior color, usually powder coating.

But be careful: in many cases, acoustic enclosures must also be connected to lightning protection.

What is often overlooked is that the powder coating has an electrically insulating effect and a very high surface resistance (greater than 1 TΩ), which is why it does not allow electrical contact for lightning protection systems. This greatly reduces the conductivity of the coated surface, and direct discharge of lightning currents via the powder-coated surfaces is not guaranteed without additional measures.

To make powder coatings conductive, special so-called dissipative powder coatings (ESD coatings) are used. These contain conductive additives. These reduce electrostatic charge and enable a certain degree of electrical conductivity, which, however, is usually not sufficiently dimensioned or specified for lightning protection systems.

For lightning protection applications, this means:

1)
Conventional powder coatings prevent a secure electrical connection due to their insulation.

2)
Contact points in lightning protection must be mechanically removed from the powder coating to establish metallic, conductive contact.

3)
Dissipative powder coatings are a special type, but are rarely used in lightning protection because they cannot safely conduct the high current loads of a lightning strike.

Summer time - time to roll out Large Heat Pumps

Mon, 09 Jun 2025 16:28:26 GMT

The summer has barely begun when we start rolling out various projects for our acoustic enclosures for large heat pumps. In June 2025 alone, the following acoustic enclosures for large heat pumps will be launched:

1 acoustic enclosure 7,800 x 4,430 x 3,440 mm L x W x H (single enclosure)
1 acoustic enclosure 6,900 x 3,800 x 3,800 mm L x W x H (single enclosure)
1 acoustic enclosure 8,900 x 6,100 x 4,100 mm L x W x H (double enclosure)
1 acoustic enclosure 10,800 x 4,800 x 3,810 mm L x W x H (double bonnet)
1 acoustic bonnet 5,480 x 2,590 x 2,788 mm L x W x H (single bonnet)
1 acoustic bonnet 18,500 x 4,600 x 4,150 mm (L x W x H (triple bonnet)
1 acoustic bonnet 3,100 x 2,200 x 2,472 mm (L x W x H) single hood

In total, the 11 large heat pumps are planned to reduce noise emissions by 209 dB(A). All of the systems are located close to sound-sensitive neighbourhoods and cannot be operated without sound measures in compliance with noise regulations. The projects are spread across Germany (Stuttgart, Berlin, Esslingen, Munich), Austria (Innsbruck) and Switzerland (Lucerne).

Around 1,350 m2 of 2 mm thick aluminium sheets and around 1,600 linear metres of aluminium profiles plus around 1,300 m2 of insulation were used to produce these acoustic enclosures. In addition, locking systems, sensors and a large number of fastening materials were used.