<![CDATA[Noise reduction for HVAC and industrial systems

<![CDATA[Noise reduction for HVAC and industrial systems - Blog]]>Mon, 31 Mar 2025 08:25:28 +0200Weebly<![CDATA[Design of acoustic enclosures for large air-cooled heat pumps and large refrigeration systems.]]>Sun, 23 Mar 2025 08:43:07 GMThttp://www.forcotech.com/blog/design-of-acoustic-enclosures-for-large-air-cooled-heat-pumps-and-large-refrigeration-systemsThe design of acoustic enclosures for large heat pumps and large refrigeration systems is based on the following parameters.

1) Physical dimensions of the systems
2) Required air volume at full load
3) Static pressure of the fans
4) Sound insulation to be achieved
5) Access required for service and maintenance work.

The following physical parameters must be set in the correct ratio during planning:

Air volume / free areas (open Areas) / air velocity / pressure loss.

Free air inlet and air outlet areas (net open areas in which the air can enter and exit the bonnet). These open areas must be dimensioned so that an air velocity of 7 metres/sec is not exceeded. This is due to the pressure loss of 28 Pa. at 7 metres/sec. This pressure loss is partially compensated for by the static pressure of the fans, which have to overcome a resistance on the evaporator on the air inlet side and have to expel the air above the fans on the pressure side.

Up to an air velocity of 7 metres/sec, the ratio between heat transfer and pressure loss is ideal. At higher air speeds, the heat transfer is negatively affected and the pressure loss becomes too high. In addition, a higher air velocity leads to flow noise which results in an increased noise level.

What does this mean for example for the design of a sound bonnet for a system with an air volume of 170,000 m3/h?

To calculate the required free area at an air volume of 170,000 m³/h and an air velocity of 7 m/s, the air volume flow must first be converted into the appropriate units in order to then use the formula for the air volume flow.

The free area for an air volume of 170,000 m³/h at an air velocity of 7 m/s is around 6.93 m².

As the exhaust air and supply air areas are separated to prevent recirculation of the air, the free area of at least 6.93 m2 must be ensured both on the intake side and at the air outlet.

]]><![CDATA[HVAC-Systems Sound Masking effects]]>Sun, 02 Mar 2025 11:18:03 GMThttp://www.forcotech.com/blog/hvac-systems-sound-masking-effectsHeat pumps and refrigeration systems are caught between energy-efficient performance and acoustic compatibility with the neighbourhood. A central phenomenon in this context is sound masking effects, which significantly influence both the technical design and the acoustic perception of these systems. These effects result from the complex interaction of different frequency ranges and operating conditions, which often lead to unexpected noise emissions, even if individual components have been optimised.

Sound masking effects describe the phenomenon in which the reduction of certain frequency ranges leads to other frequency components being perceived subjectively louder. This effect is based on psychoacoustic interactions: The human ear is less able to localise low frequencies and perceives them as more dominant when the background noise is reduced.

With heat pumps, such effects are typically caused by:

1
Frequency overlaps between fan noise (usually medium to high frequencies) and compressor noise (low frequencies),

2
Operating state-dependent modulation as typically occurs during de-icing cycles, in L/W heat pumps where fan speed changes shift the frequency spectrum.

3
Reflection from building structures that amplify certain frequency bands through constructive interference.

Air-to-water heat pumps emit sound in the range of 30-70 dB(A), with the critical frequency bands lying between 63 Hz (low humming) and 4 kHz (high humming). Masking effects occur in particular when high frequencies are attenuated by sound insulation measures, making low frequency components more prominent in relative terms. For example, attenuating a 2 kHz signal by 10 dB(A) can result in a 100 Hz hum being perceived as 6-8 dB(A) louder

One of the main causes of masking effects are thermodynamically induced changes in operating conditions. At air temperatures around 0°C with high humidity, ice forms on the evaporator fins, which leads to the following effects:

4
Pressure losses in the air flow force higher fan speeds (frequency increase of 15-30%).

5
Compressor load changes when switching to defrosting modes generate pulse-like low-frequency oscillations

6
Material expansion on iced components cause additional resonances in the 80-200 Hz range.

These dynamic changes are superimposed on the basic noise spectrum and lead to non-linear masking effects that can hardly be detected by stationary sound measurements.

The interaction of these spectra leads to complex superpositions. For example, the 100 Hz component of the compressor can suppress the perception of 800 Hz fan sounds, while at the same time harmonics at 1600 Hz are amplified by resonances in the housing.

]]><![CDATA[AI-Tools and planning acoustic enclosures]]>Sun, 02 Feb 2025 09:03:08 GMThttp://www.forcotech.com/blog/ai-tools-and-planning-acoustic-enclosuresThe use of AI tools is already saving us a lot of time in the planning, design and production of our acoustic enclosures for heat pumps and refrigeration systems.

The calculation of fan key figures, air volumes, pressure losses and, for example, optimum air speeds, can be greatly accelerated through the use of AI. Furthermore, the targeted use of AI tools simplifies the prediction of noise emissions and noise immissions, taking into account various atmospheric and topographical conditions.

The use of AI in production serves to optimise the four-cutting of raw materials such as insulation, aluminium sheets and frame profiles, thereby shortening production planning.

The use of AI does not solve any questions that cannot be answered without AI, but it speeds up the process of finding answers enormously.

Perplexity's announcement to integrate ‘DeepSeek R1’ into its AI platform offers the possibility to access DeepSeek's logical capabilities within the Perplexity framework, which promises to further optimise the performance of AI tools for mathematical and physical problems for the benefit of planning technical building services engineering.

]]><![CDATA[Hamburg - Workshop]]>Sat, 01 Feb 2025 14:08:00 GMThttp://www.forcotech.com/blog/hamburg-workshopWe spent the last two days of January in Hamburg discussing future projects, changes and optimisations in our company.

We focussed in particular on current and upcoming projects. We discussed specific optimisation measures to make our processes even more sustainable and efficient, with a focus on the use of AI. The digital integration of production and installers was particularly valuable in order to develop the best possible solutions for our customers.

Finally, we visited a property where our acoustic bonnet for two large heat pumps will be installed in the coming weeks - a measure that both reduces noise emissions and optimises energy efficiency.

With lots of new impetus and a clear vision, we are motivated to take the next steps.

]]><![CDATA[installation distances between refrigeration systems and heat pumps.]]>Sun, 05 Jan 2025 19:38:00 GMThttp://www.forcotech.com/blog/nstallation-distances-between-refrigeration-systems-and-heat-pumpsMore and more often, we are forced to plan several refrigeration systems or heat pumps in a relatively small area.

In most cases, the arrangement of the system is therefore planned on the basis of the available space.

This one-sided focus can have drastic effects on the free air exchange of the systems, both for the supply air and the exhaust air of the systems.

The architectural and atmospheric conditions around the systems can have a massive impact on their performance. Recessed roofs and walls, for example, can have a negative impact on the air flow due to turbulence. On the air outlet side, recirculation of the exhaust air can lead to a massive loss of system performance due to the higher air inlet temperatures during heat transfer.

Another factor that is not often taken into account is the distance between the units, which not only influences the air flow, but can also lead to a massive recirculation of the exhaust air depending on the wind conditions. If the systems are installed one behind the other, the advantage is that the air flow remains free on all sides (Fig. 1). If the systems are arranged next to each other, it must be taken into account that, for example, with 3 systems, both sides of the air flow with the centre system are in the intake area of the two opposite systems (air shadow). Depending on the air volume of the systems, the distance between the systems must therefore be planned to be considerably greater than if they are installed one behind the other. (Fig. 2).

The design of the systems is also a decisive factor in the arrangement of the systems. A particular example are systems in table-top design, often drycoolers whose condensers are usually installed a short distance from the floor (Fig. 3). If such units are installed too close to each other, the air flow of the supply air is negatively affected during simultaneous full-load operation, i.e. the inflow area is too small, which can lead to a reduction in performance of the units of up to 30%. One way of installing the units closer together is, for example, to elevate them on a grating to increase the air inflow area from below (Fig. 4). An additional advantage of elevation is the greater ground clearance which, depending on the nature of the substrate, e.g. soil or grass under the grille, also has a positive effect on the delta T between the supply air temperature and the cooling temperature, as soil heats up significantly less in direct sunlight than a concrete substrate, for example. In terms of sound, soil also has the advantage of absorbing sound and not reflecting it, as is the case with a sound-reflecting surface such as concrete.

]]><![CDATA[Ejectors for heat pumps]]>Sun, 05 Jan 2025 19:31:22 GMThttp://www.forcotech.com/blog/january-05th-2025Ejectors in heat pumps
Ejectors are innovative components that are used in heat pumps to significantly increase their efficiency. They enable a significant increase in efficiency by optimising and partially recovering the compression work required in the compressor.

How ejectors work
Ejectors work according to the Venturi principle. A high-pressure flow is accelerated through a nozzle, which leads to a drop in pressure. This pressure drop creates a vacuum, which makes it possible to attract a low-pressure flow (suction flow) that mixes with the high-pressure flow. The kinetic energy in the diffuser is then converted back into pressure energy, which leads to an increase in the pressure of the total mass flow.

Advantages
By recovering throttling losses, part of the compression work can be saved, which increases the overall energy efficiency of the heat pump

Ejectors can significantly reduce the required power of the compressor or even replace a compressor stage in multi-stage systems.

Ejectors allow adaptation to different operating conditions and can be used in different configurations to optimise performance.

Challenges
Despite their advantages, ejectors are not yet widely used in practice. Ejectors need to be precisely matched to their operating conditions, which places high demands on the design. Furthermore, uncertainty about the cost-benefit ratio is one reason why many manufacturers do not implement this technology.

Overall, ejectors offer promising opportunities for increasing efficiency in heat pump systems, but require further research and development in order to optimise their application in industry and make them economically attractive.

]]><![CDATA[HVAC Equipment Noise proofing and sensors]]>Tue, 10 Dec 2024 17:23:32 GMThttp://www.forcotech.com/blog/hvac-equipment-noise-proffing-and-sensorsNoise protection measures are an important issue today when planning larger heat pumps, VRF/VRV and refrigeration systems. This is due to denser construction, greater sensitivity of the population to the environment and therefore also to noise, and stricter regulatory requirements.

In many cases, this not only affects new systems, but also systems that are already in operation.

This is where modern acoustic arbours come in, which not only aim to reduce noise emissions, but are also equipped with appropriate sensor technology to enable better control of the systems, monitoring of energy efficiency and early detection of anomalies in system operation.

(1) /(2) Sensors for controlling the air inlet and outlet openings

Control of the position of the air inlet and outlet louvres of the acoustic bonnet to optimise the air flow. The louvres can be set to 4 different positions via sensors to control the air volume flow:
Closed louvres = example for cold start of a heat pump at low outside temperatures / 45° = normal operation of the system up to 50% air volume / 60° = normal operation of the system up to 80% air volume / 90° full load operation or ‘Free Cooling’ mode for refrigeration systems.

(3) Refrigerant sensors

Early detection of refrigerant losses and prevention of compressors running dry. Positioning of the sensors depending on the specific weight of the refrigerant. For systems with flammable refrigerant in combination with storm ventilation to prevent the accumulation of an ignitable quantity of refrigerant.

(4) Air pressure sensors

Air pressure sensors for measuring pressure losses and air velocity enable the systems to be optimised. The air velocity can also be optimised by combining this with controlling the position of the air inlet and outlet fins.

(5) Sensor technology Measurement of temperature, humidity and sound

Are a standard application in sensor technology. The air inlet temperature with the comparison of the temperature of the system's exhaust air is another way of identifying potential for optimising the systems.
In future, the recording of acoustics during normal operation of the system with the ongoing adjustment of the acoustics during operation of the systems will be a possibility for the early detection of system faults, even in the event of the smallest acoustic change.

(6) Sound insulation on the inside

StratocellWhisper-FR-400 mm

]]><![CDATA[continuously recording and analyzing noise and vibrations of HVAC Equipment]]>Fri, 26 Apr 2024 08:43:56 GMThttp://www.forcotech.com/blog/april-26th-2024The acoustics of systems can be an important indicator of the condition and performance of HVAC systems and machines in general. By , anomalies can be detected and potential problems identified at an early stage.

This method is referred to as “Acoustic Predictive Maintenance” and is an example of predictive maintenance that will replace “preventive maintenance” concepts in HVAC systems.

“Acoustic Predictive Maintenance” is a method based on the analysis of noise and vibrations. The continuously recorded machine noises are compared with the noise data from normal operation in order to derive statements about the operating status. Noise and vibration analysis is used to detect anomalies and identify potential problems at an early stage. The data is evaluated in real time and compared with the reference data. If deviations are detected, suitable measures can be taken to prevent or minimize damage.

By evaluating acoustic data in combination with information from air pressure, refrigerant, humidity and temperature sensors, HVAC systems can be monitored virtually seamlessly in real time, reducing unplanned downtime, extending the service life of systems and cutting maintenance costs.

]]><![CDATA[System maintenance and energy efficiency]]>Mon, 25 Dec 2023 09:48:59 GMThttp://www.forcotech.com/blog/anlagewartung-und-energieeffizienzEnergy-efficient refrigeration systems and heat pumps are not just a question of the latest compressors, fans or refrigerants; the issue stands and falls with the maintenance of the systems.

The picture below shows an evaporator of an industrial process cooling system where we have installed a sound enclosure. After removing the protective grilles in front of the evaporator, we found it to be completely dirty. Practically no air was passing through the evaporator fins and the system was constantly running at its limit in order to generate any cooling capacity at all. This not only has a negative effect on the cooling capacity, but also results in higher power consumption (current).

The picture next to it shows the evaporator after cleaning, with the evaporator fins once again air-permeable.

Important: the evaporator fins must be cleaned against the direction of air flow (blowing out). We must warn against mechanical cleaning with a broom or a high-pressure cleaner from the outside, as this only leads to the dirt accumulating between the fins and thus the dirt only being relocated.

]]><![CDATA[Acoustic bonnet for a dry cooler]]>Sun, 01 Oct 2023 06:51:54 GMThttp://www.forcotech.com/blog/schallhaube-fur-einen-ruckkuhlerInitial situation
As part of the refurbishment of the first floor of the Bubenberghaus on Schanzenstrasse in Bern, the cooling system is also being replaced and extended. The capacity of the cooling system was increased compared to the previous system, which meant that the precautionary noise values were not met. The recooler is used to cool the entire building, but in particular the MRI systems of the radiology centre located in the building. Noise emissions must be reduced by at least 14 dB(A). This is achieved by using the installed acoustic bonnet.

The recooler has the following dimensions: 7,646 x 2,420 x 2918 mm (L x W x H). The system has 12 EC fans. The total air volume of the system at full load is 220,000 m3/h.

Sound enclosure concept
The basic structure of the sound enclosure consists of 6 modules of an aluminium plug-in profile frame that are connected to each other in place. The service doors around the system were integrated into the profile frames. The inside of the doors is lined with 40 mm ‘StratocellWhisper’ insulation. The acoustic bonnet was built from 6 modules that were simply mounted on top of and next to each other and statically reinforced. The air chambers between the supply and exhaust air are hermetically separated by the use of separating panels that run in a rail system of aluminium U-profiles. The panels can be opened at some points so that access to the fans is possible at any time.

The assembled modules have the following dimensions:
9,446 x 4,100 x 3,618 mm (L x W x H) with a weight of 2,040 kg.

The air outlet speed at full load is around 10.2 metres/sec.

In terms of energy, it is interesting to compare the ambient air temperature with the temperature of the air entering the condenser. Despite the relatively high air inlet velocity, this is around 5.4° Celsius lower than the air temperature outside the bonnet.

The reason for this is obviously the shading of the condenser on all sides in combination with the movement of the air, which leads to this relatively high cooling of the air as it enters the condenser. This will also have a positive effect on the cooling capacity and power consumption of the dry cooler.

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