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Beginners guide to acoustic fans. Selecting the right equipment for your Acoustic fans system can be tricky. For most people it starts with looking up the db rating of the fan and ends with them scratching their heads wondering why its so loud when it said it would be so quiet... There are many variables to consider when trying to keep the noise output to a minimum. Airflow Bends/Tees and Splits Duct Diameter Duct Insulation Duct Routing Grills/Diffusers Fortunately for every cause there is usually a simple solution, We are going to explain what you can do to limit the noise output from your extractor system Acoustics in extraction systems can be one of the hardest jobs to get right the first time. With a little bit of research, patience and experience you should find it a breeze. There are going to be times where powerful air extraction is required with minimum noise pollution. Here at Just Fans we can help you! We have experience supplying to Recording Studios, Doctors Surgeries, Hospitals and more. Trust us for expert advice with your HVAC Requirements via Telephone E-Mail or Fax 9am - 5:30pm Monday to Friday The Basics Selecting a quiet fan This should be a consideration but there are reasons why the listed db rating will not always help. The figures listed below are for a general guide to how noisy the fan is in operation, This can be deceiving as the fan may be secured in a loft space, wall or ceiling cavity for instance, which will add to insulating the fan motor, but will have no effect on the inlet/outlet noise which is commonly neglected. The most important part of the system to consider (if the fan is not going to be in the same room as you) has to be the inlet/outlet grills. 70-90% of the sound you can hear at the source is usually the air passing the grill/diffuser. This is quite easy to overcome. The first thing you can think of trying is to have a larger grill than you would normally. The more surface area around the grill, the less resistance and therefore less noise is given off by the airflow as it passes into the duct. A reducer can be used to connect the larger grill to smaller sizes of duct, This has 2 benefits, Not only does it allow more airflow with less resistance, in most cases it does cause the final bend in the duct run to be further away from the grill. As the duct connects from a typically horizontal layout, to a vertical connection (the ceiling grill/diffuser) a bend is unavoidably created. The further any bend is from any grill or diffuser the better. Grills/Diffusers/Inlets/Outlets 70-90% of the sound you can hear at the source is usually the air passing the grill/diffuser. This is quite easy to overcome. The first thing you can think of trying is to have a larger grill than you would normally. The more surface area around the grill, the less resistance and therefore less noise is given off by the airflow as it passes into the duct. A reducer can be used to connect the larger grill to smaller sizes of duct, This has 2 benefits, Not only does it allow more airflow with less resistance, in most cases it does cause the final bend in the duct run to be further away from the grill. As the duct connects from a typically horizontal layout, to a vertical connection (the ceiling grill/diffuser) a bend is unavoidably created. The further any bend is from any grill or diffuser the better. Bends, Tees & Splits T and Y Pieces should be used for their correct purposes! T Pieces are used when a system needs more than one inlet into a single duct run. Y Pieces are used when connecting 2 ducts/fans together onto a single outlet Wherever a bend, Y or T piece is used you need to consider its impact on the duct pressure. Bends cause the air to rapidly change direction, This can be detected as audible noise in and around the areas of the bend, also where the air leaves the system. You can keep the effects to a minimum by having long sweeping bends rather than being tight and abrupt (Bends more than 90 degrees can cause lots of noise and very poor performance). Insulating around the bend with loft insulation will help dampen any transferred noises through the ceiling and if you can, try and keep the final bend as far back from the grill as possible, It can be worth suspending the duct up high so the final length to the grill is as straight as possible. Duct Routing If you want to have 2 outlets in a single room with just one fan it is best to have a simple Y piece system, This allows 2 ducts to be in opposite ends of the room and keep the fan somewhere centrally, This type of duct design can be quite fool proof as it reduces the pressures going through each grill (Don't forget the bends tho, you are adding an extra). Typically you will only really have problems when trying to duct 2 fans into a single Y piece. The two airflows will struggle to cope if leaving on the same size duct. In this situation you should consider increasing the duct on the outlet side, This will let the airflow pass without increasing the pressure too much. Like water air can only travel so fast through something without it accelerating and building pressure. To keep noise pollution to a minimum try and allow adequate diameter duct to handle both fans. So for instance 2 x 100mm fans would want 1 x 200mm output. Duct Routing is very important. As previously explained you should be aware of any bends or kinks in the system. Try and keep it as straight as possible. Where it runs in cavities or loft spaces above or around living areas you might wish to consider Acoustic Duct, This allows the noise to be absorbed into a fibre glass type intermediate layer via small holes perforating the inner lining, This helps stop noise being present at the grills and from seeping throughout the duct run. Silencers perform a similar role and can be used very effectively. This just leaves us with Airflow. Quite Simply.. The faster air moves, the louder it is going to be. Over spec the fan and use a speed controller to lower the speed, A larger fan on low speed will out perform a small fan on full speed! While it is possible to have a high airflow and low noise output you can see how hard things are working against you. This is why we are here to help.
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