At first glance, the answer to this question seems relatively simple. After all, there are many programs on the market for selecting noise silancer from various manufacturers. However, the issue is more complex than it appears. Why? Because none of these programs address a critical question from the perspective of an HVAC/MEP designer, namely: What noise level will be established in the room?
The available noise silancer selection programs only provide an answer to how many decibels (dB) the noise will be reduced behind a specific noise source. From a designer’s perspective, this information alone is often not sufficient.
The only way to answer this question is to perform calculations that consider not only the noise source and silancer but also the impact of noise attenuation through the installation and the propagation of noise within the room itself. This is because the same diffuser will "sound" differently in a well-damped room with a large volume compared to a raw, small-volume space.
How to approach this correctly?
One way is to use the KSC and KOA modules of the IX-CHART program.
With KSC, you can not only perform hydraulic calculations for the installation but also calculate the attenuation properties of the system itself. If you need additional information about concepts related to acoustics, I invite you to read the article at the link below: Acoustics in HVAC - What You Need to Know About Noise Below is a simple calculation example that demonstrates step-by-step how this can be done using the IX-CHART program:
Assumptions:
We consider a ventilated room with:
Airflow rate: 300 m³/h
Dimensions: L x W x H = 6 x 6 x 3.5 m
Volume (V): 126 m³
This room represents a typical office space characterized by a sound absorption coefficient (α): 0.15, which corresponds to a room with carpeting and furniture.
The diffuser will be centrally located in the room and will have the following acoustic parameters (the selection below comes, for example, from the Easy Product Finder 2 program by Trox):
and the following directional propagation coefficient depending on the location of the diffuser in the room:
A duct fan with an airflow rate of 300 m³/h and a pressure drop of 150 Pa is used. For this example, I have selected the RM 160/650EC fan from Harmann, which has the following acoustic parameters:
Remember: When it comes to devices, we are always interested in the SOUND POWER LEVEL Lw(A) or Lw, not the sound pressure level, because in the case of the sound pressure level Lp(A), the device manufacturer has already made certain assumptions about room attenuation, etc., which can lead to different results in every scenario.
The sound pressure level is only relevant concerning the end user of the room, as ultimately, that is what we care about. However, to calculate that, we base our calculations on sound power levels.
Important Notes:
If the fan is located outside the room, there is no need to account for noise through the fan casing. Instead, focus solely on the noise emitted through the OUTLET of the fan, as the calculation pertains to the room, and we are not concerned with noise propagating toward the intake side.
4. Noise silancer
5. Ducts Here we have only 10 meters of round ventilation duct and 1.5 meters of flexible duct.
So let's get to work – having all the parameters and assumptions, we launch the KSC module of the IX-CHART program and input all the data:
1. Fan:
2. Noise suppressor
3. Ducts:
4. Air diffuser:
In this way, we obtained the results in the form of a table, which we can copy into the KOA module.
In the KOA module, simply click on the calculations, and the result is ready – at a distance of 2 meters from the diffuser, the sound pressure level will be Lp(A) 29.5 dB(A), which can be considered a good result.
Okay, what would happen if there were no noise silancer? Let's check it. I remove all values related to the noise silancer's attenuation and its own noise, and I get the following results:
The result is Lp(A) = 39.2 dB(A).This means that our noise silancerreduced the noise level by 9.7 dB(A), and this is the answer to the question of whether the silancer was selected correctly. In our case, yes, but if anything in the room were changed (volume, absorption coefficient, etc.), the result could be quite different, and the silancer would need to be adjusted.
As you can see, using the IX-CHART program, this is quite simple, but it does require time.
I invite you, dear reader, to download the program and explore the tool on your own.
Thank you for the kind offer! I’m glad I could assist you, and I appreciate your support for the development of this portal. While I can’t physically accept a coffee, your words mean a lot, and I’m always here to help whenever you need it. 😊 Keep exploring and feel free to reach out anytime!
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