When I started in this business 20 years ago, noise wasn't really an issue. Now, it's becoming a more prevalent concern in our industry. In fact, the World Health Organization classifies noise as a type of pollution. The equipment that we provide institutions such as hospitals, universities, and pharmaceutical companies, must be as quiet as possible. These buildings are located in urban areas, so as design engineers and fan manufacturers, we have to create equipment that meets very strict criteria.
Fan manufacturers (including ourselves) test equipment not only for air performance, but for sound. We send the equipment to a test lab for certification. In our case, we send it to the Air Movement and Control Association (AMCA). The results will give the subjective noise of the equipment.
It's up to the design engineer to decide what's a permissible sound level for the particular project the equipment is being used for. It could be a simple case of choosing the right type of fan, since various fans have different sound characteristics. (Some are noisier than others.) Propeller fans tend to be noisy, while centrifugal fans with airfoil wheels tend to be quieter. When a project requires that you stick with a particular design of fan and there is a sound issue, you can decide which options to take advantage of in order to reduce the sound.
One option is to choose a fan that's one or two sizes bigger in order to reduce the speed, and consequently, the noise. You can usually reduce it by a few decibels, which might make enough of a difference. Otherwise, another common and straightforward approach is to use some form of sound attenuation. (These are essentially silencers.) A good analogy that's somewhat similar is the muffler you have on your car.
Attenuators come in all shapes, sizes, and materials. They are essentially a double-wall barrel with a perforated liner on the inside and acoustical media between the inside and the exterior wall. These silencers go either on the outlet or the inlet of the fans and they can actually reduce the equipment noise anywhere from 10 dB all the way up to 30 dB.
Like with most things, the more you spend and the bigger the attenuator, the more noise reduction you can achieve. Some attenuators are very small, weighing a couple hundred pounds. Others are so big and heavy that they need additional structural support off of the fan to be able to support the weight.
The best advice I could give for any end user, design engineer, or architect is to address the sound issue before you buy the equipment. Know what the sound requirements are for your application beforehand. Once the equipment is onsite and up and running, it will be very difficult and expensive to fix noise issues if neighbors around the building start to complain.
Of course, it's impossible to have perfectly noiseless equipment, since these are mechanical objects. However, we try to make our products as quiet as possible, just like any other fan manufacturer.
To learn more,we use in our products.
Ken: And we're back with Simon Davies of MK Plastics. Simon, today you wanted to speak with us about sound and how MK Plastics can help facilitate the remediation.
Simon: That's correct, yeah. When I started in this business 20 years ago, sound was not really an issue. It was there, but now it's becoming more and more prevalent in our industry. In fact, the World Health Organization classes noise as a type of pollution. So the equipment that we provide our institutions such as hospitals, universities, pharmaceutical companies, and these buildings are in urban areas and so the, as design engineers and fan manufacturers, we have to design and manufacture equipment that can not only function properly on what they're supposed to do, but also as quiet as possible and for that reason, fan manufacturers including ourselves test their equipment not only for air performance, but for sound and you send the equipment to a test lab, in this case, AMCA certification for sound. So that gives the subjective sound, noise of that equipment. Now it's up to the design engineer to decide what is the permissible, permitted sound levels required for that particular project. It could be a simple case of choosing the right type of fan. Different fans have various sound characteristics. Some are noisier than others. Propeller fans tend to be noisy. Centrifugal fans with airfoil wheels tend to be quieter. But sometimes, when you have to stay with a particular design of fan and there is a sound issue, then you have to decide, well, what can I do to reduce that sound and that's where certain options are available for sound reduction.
Ken: Well, what options does MK Plastics bring to the table for sound remediation?
Simon: Well, first of all we always recommend, obviously, as I said, choose the right type of fan. But, if you have a particular fan in mind, perhaps choosing, a simpler way is to choose a fan maybe one or two sizes bigger to reduce that speed and that noise. You can reduce it by a few dB, decibels, that might make a difference. If you cannot, then the simplest approach and the most common approach is to use some form of sound attenuators, attenuation, and these are essentially silencers. A comparison would be similar to the muffler you have on your car and they come in all types of shapes and sizes and materials and it's essentially a double wall barrel, want for a better word, with it's got a perforated liner in the inside and acoustical media between the inside and the exterior wall and these silencers go on the outlet or the inlet of the fans and they can actually reduce the sound noise of the equipment quite a lot from anywhere from 10 decibels sometimes all the way up to 30 decibels. Like anything, the bigger, the more you spend, the more noise reduction that you can achieve. Some of them are very small. Some of them weigh only a couple hundred pounds. Some of them are so big and heavy that they need additional structural support off the fan to be able to take the weight of them. So, there are silencer options that you can use to reduce the sound in an application.
Ken: Has there ever been a circumstance or an installation where you needed to reach near 0 dB and can you do that?
Simon: No, that's impossible. It's a mechanical piece of equipment. It makes a noise. We try and make our fans as quiet as possible, like any other fan manufacturer, but it's impossible to get it down to 0 decibels. I mean, you try your best to reduce it as much as you can with sound attenuating options that are available to you.
Ken: Is there anything else you'd like to share about sound and how to remediate the issue?
Simon: The best advice I could give is for any user, end user, or design engineer or architect, address the sound issue beforehand, before you buy the equipment. Know what the sound requirements are, address it beforehand because once the equipment's onsite, up and running and then people and neighbors around the building start complaining, that's where it gets very difficult and very expensive to fix it. Address it beforehand, not after the fact.