Quote:
Originally Posted by
jpmch
Dan, no problem, I appreciate your latest response very much.
I've attached all the specs I have on the fan - it's the 150mm model.
I must admit I am struggling to come up with the exact design of the box. My builder is waiting for me to confirm in the next two days.
I've agreed with him that the top and one side of my boxes will be the inner ceiling and wall, which is made up of 2 layers of fire board with green glue between, a layer of 18mm OSB, and 100mm RW3 insulation behind.
So it will be the front side, bottom and end sides that are made and secured to the wall and ceiling, then caulked. These will be made of MDF with 2 layers of fire board green glued together (see second drawing attached).
But, as I say, the exact design - dims, lengths of baffles - is something I really could do with some help on.
thanks
John
It's ok to use the wall and ceiling as part of your silencer providing you can get a completely air tight seal when attaching it. Also some inner baffles will need to attach to the wall, so you could use brackets to screw them to the wall before caulking and attaching the final mdf face.
I find them easier to build on the floor though in mdf as a complete box and then beef them up once attached to the wall.
So using a similar design to Rod you could do this:
Your fan provides 600m3/hr, through 150mm round duct this is 17600mm2 or 0.0176m2.
600 / 0.0176 gives 34090m/hr or 9.5m/s flow rate.
Rod recommends as close to (0.51m/s) 100FPM as you can get but definitely under 300FPM (1.52m/s).
Have you already bought the fan or can you get the size up and run it slower?
Do you need to run the fan at full speed? (To maintain more than 6 room volume changes per hour)
If so you'll need to drastically increase the duct size in your silencer to slow the air velocity and make it quieter. If you don't you'll hear the air rushing in through your inlet and sucking out of the extract.
To get 600m3/he under control your diffuser(s) will need a free area of around 0.16m2, 400mm square would get that. (Some diffusers only have 50% free area of their face size so you'll have to check though.
So your first and last sections of your silencer should be 400mm in width and 400 height or rectangular with an area of 16000mm2 or there about. You could reduce this to 200mm x 400mm at the baffles and the middle sections open out to 250mm x 400mm.
They wouldn't need to be this big obviously if you don't need 600m3/hr and can reduce the speed.
Dan
Ps. Budding studio builders out there, if your studio is big enough to need 600m3/hr, consider running silencers to 2 separate diffusers for inlet on opposite walls, as the diffusers won't throw very far with the reduced velocity we require and you'll get hot/cold spots in your room.