Every day people commute to work and back home using trains in a form of subway systems. These types of system can create noise both to the passengers inside of the train as well as to the environment.
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One of the things that becomes an unpredictable issue of a building, especially with a centralized air conditioning system, is the noise it creates. Calculating noise from every part of the HVAC system is needed to avoid unwanted noises in adjacent rooms.
What do we need to know to avoid noise from the HVAC system?
Are there simple steps to avoid it?
In this article, we will discuss about the noise that occurs in the HVAC system and how to avoid it.
Every sound that is heard can usually be identified through its frequency range. In relation to frequency range, noise that occurs related to the HVAC system is divided into 3 categories within the frequency range:
- Low Frequency
Fan Noise, it generally produces sound from 125 Hz to 500 Hz octave frequency bands. Variable Air Volume (VAV) boxes noise is usually from 125 Hz to 500 Hz octave frequency bands.
- Mid Frequency
Airflow Noise and turbulence-generated noise in a duct range from 31.5 Hz to 1000 Hz.
- High Frequency
Damper and Diffusers Noises, they usually contribute to the overall noise in the range of 1000 Hz until 4000 Hz octave bands.
All the noise above can be avoided if we know how to design HVAC system acoustically and each of these issues must be addressed:
- Duct-borne Noise
The sound generated by the fan will travel along with the ductwork both upstream and downstream easily because the velocity of sound is much greater than the velocity of air in ducts.
- Radiated Equipment Noise
Radiated equipment noise transmits through the wall or floor into the adjacent space or in the case of rooftop equipment to the environment. It is generated by vibration of the fan casing and motor.
- Duct Break-in Noise
Noise inside ceiling plenums or from air conditioning equipment, plant room, etc, can break into the duct and then be carried into rooms or spaces downstream. So, where possible, avoid ducts passing through noisy areas as this can significantly increase noise through the air conditioning system, avoid lightweight ducts as well, replace them with heavier ducting such as sheet steel.
- Duct Break-out Noise
Along with the ductwork, however, transmits through the wall of the duct, thus impacting the adjacent space. Generally, it happens from noise passing through the duct, aerodynamics noise from obstructions fitting in the duct, and turbulent airflow causing duct walls to vibrate and rumble radiating low-frequency airborne noise.
- Terminal Noise
The final links in the distribution chain are the terminal air devices. These are Grilles, Diffusers, Registers, and Vent Cover that go over the duct opening in the room. Streaming air noise from diffusers and from transitions can cause additional noise in the receiving room. So that for this issue, we need to concern choosing the proper specs of supply and return air devices. We need to try to find out the NC (Noise Criteria) rating for them from their respective manufacturers.
By knowing those 5 ways of how noise occurs, it makes easier for us to categorize noise that will produce in our HVAC system design and help us in choosing what material, enclosure, duct shape and everything we need to reduce noise.
We believe that the best way to be highly productive is to be able to get into our monoideal state. Josh Kaufman says in his book “The Personal MBA”:
“Monoidealism is the state of focusing your energy and attention only on one thing. It’s often called a “flow” state: clear, focused attention on one subject for a long period of time.”
For this to happen, potential distractions and interruptions need to be eliminated. This is the reason for some people, working early in the morning or late at night can feel very productive – because on a normal day, no one is going to call you at 4 in the morning.
However, most of us do our work in an office which does not operate at those silent, undistracted hours. The good news is, we still can manage our potential distractions by knowing what distracts us the most. This can be done by allocating a time when you want to be in your monoideal state and free yourself from distractions during that time. For example, you can put your phone into flight mode and turning off email notifications from 8 to 11 and start to check emails and communicating with the outside world from 11 until lunch. The timing will depend a lot on the type of work you are doing and how much time will you need to be in monoideal state.
Unfortunately, there are things that is out of your locus of control – there is a retrofitting job upstairs, your co-worker decided to sing along to the song he is listening to, people in the other room are laughing loudly (are they talking about their boss?) and so on. If it’s not in front of your eyes, for example pop-up notifications on your screen, most of the distractions come to you in a form of sound, or I think it’s better to call it “noise”.
Noise is a productivity killer that you might be overlooking, especially if you have passed the stage of being distracted by your phone, browsing Facebook on your computer and looking at cat videos on Youtube. Fortunately, noise is manageable in a few different ways. The most viable option for an existing office is to make noise-related rules and to make everybody aware that noise can reduce their productivity. For example, companies can make rules that retrofitting job, singing and gossiping must be done outside of office hour. Another way to fix this is to separate areas for people who want to be focused and areas where people can socialize and discuss with their co-workers.
The best way to manage noise? Is to take noise into consideration from the beginning of the design process of the working space. This can be a long and complex process where there are a lot of aspects to be considered in designing an ideal office. It needs a balance between visual pleasure, company’s philosophy, functionality, health, safety and all other aspects that we want to take into account. A lot of times, all those aspects will relate to noise or acoustics in some ways, depending on each unique case.
For us acousticians, these are the things that we typically think about when helping others to design their working space (and actually any other built environment):
- Ambient noise: We want the noise level inside of the working space to be reasonably low, whether it is intrusion from outside such as traffic, railway, aircraft and neighbouring building (neighbour’s mechanical system can be quite noisy), or the noise from inside the building such as HVAC system and lifts.
- Sound insulation: We don’t want to hear sound that we don’t want to hear from the next room, upstairs or downstairs. By designing a suitable ceiling, flooring and wall systems, a sufficient sound insulation can be achieved.
- Room acoustics: We want to be able to listen comfortably and understand verbal information that we want to. This is critical especially in meeting rooms and event space.
- Sound reinforcement and public address system: We want the sound reinforcement and public address system to be heard clearly while not disturbing others who don’t want to hear it.
All the above can also be done after the building and the working space is built. But if it’s done before it’s built, you will have a lot more options and be more cost efficient rather than changing what is already been built.
So, if you are a highly productive person, or if you want to become one, we would suggest you to consider noise in choosing the space you are working in.
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