air noise question

[houdini]

I'm in the process of moving my growroom. We have a good location for the new one, the only problem is the proximity of a couple of open windows (on warm days) about 30 feet from the growroom. My question is concerning exhaust air noise. I'm going to be using a 1500 cfm fan to exhaust warm air through a window opening. The actual window frame itself is going to be boarded up and I'm making a wood box to surround the open window portion. The wood box will have a 12 inch hole cut in it to mount exhaust ducting. Does anybody have experience of using large centrifugal fans in a similar setup ? Minimizing noise is really important. I'm aware of all the things to reduce noise such as sono-ducting, air silencers, etc. however I would hate to have a knock on my door from a neighbor asking why I'm running a jet engine in my room ! BTW I haven't actually heard a 1500 cfm fan running so I hope somebody here can tell me I'm being paranoid :D

[babystarbud]

my friends set up has an inline silencer on his ducting, it is quite bulky....
looks kinda like a big version of a baffle box that you would find on a car exhaust, but its made specificly for ducting.

same principal i guess

i would think if your hydro shop cant help you out, you would have to look at industrial air/con suppliers but there are solutions out there.
if you could figure out how they are constructed, im sure you could make a home-brew one without too much hastle.

hope thats of some help

[babystarbud]

ive just done some calculations, my fans 125m3 per HOUR, which ive worked out is 147cfm

shit thats a big ass fan...do you really need one that big? whats your set up?

[babystarbud]

p.s. i dont think it will sound quite as bad as a jet engine, more like a single engine cessna, the drug smugglers aircraft of coice....lol

[harris7]

centrifugal fans are very quiet. it's there biggest benefit.
you can also hand the fan by bungees which will absorb the vibrations

I find using plastic ducts absorb a lot of sound. I sleep in the same room as my grow so
I would know. The aluminum ones make the most noise.

You can also considering blasting metallic when ever the fan is on.
Your neighbors will be so distracted by that, they wont care about fan noises

[dusto2k3]

yeah, you can build a box to put the fan in. It would help. You will have to somthing about that noise. I run a 449CFM centri. fan and you can hear it through a bedroom door. I would hang my 1500cfm fan in box

[dusto2k3]

what harris said about the radio is a great idea, you wouldn';t have to blast, just loud to blend with the purrrrr of the fan

[razzapiggy]

Also hanging blankets inside the grow room on the walls will absorb a ton of noise! Best of luck

[houdini]

Thanks a lot folks for your kind replies. I appreciate the noise INSIDE is a consideration which I can deal with. My biggest concern is the roar of the air as it exits the window. Will a silencer on the o/p of a 1500 cfm fan reduce this so that folk behind windows 30 feet away will not be curious (or pissed off !).

[trynagethigh]

If noise is of serious concern make sure you do not make any reductions in the exhaust, in fact if you can start expanding the size of the exhaust as soon as it leaves the fan. This way you are actually lessening the restriction and giving the air more room to disperse and not less thus creating less pressure. More pressure and restriction mean more noise. What about splitting off the exhaust to two locations instead of one if possible.

Tryna

[babystarbud]

a silencer will help, but again...do you really need a fan that powerfull....how many lights are you running? what wattage?

[houdini]

I'm running 6000w ( 6 lamps) of HPS light in a 25ft. x 25ft. room. I need to empty the room in about 4 minutes and that requires a large fan.

[Garden Knowm]

Hello Houdini...

I had a 2000 CFM fan running with 16 inch ducting ...20 feet... The five OH came to the house one day.. NO problem.. no noise.. nothing...

I mounted the EXHAUST using a bicycle tire and spray foam,.. this reduced the vibration and noise!!!

NOW.. there are other prioblems using such a big fan.. it will fOOk the air flow up in your entire HOUSE.. no more fires in the fire place.. and many doors will get bent over several months of intense suction..

If you use a speed regulator on your fan.. it will probably make more noise at slower speeds..

iloveyou

[trynagethigh]

Man for that kind of setup I would run a duct straight up through the walls through to the attic roof and possibly use a whole house fan (attic fan) to pull the air instead of pushing it out with such great volume. This way you can use a smaller fan pushing (less noise) if you have a nice size one pulling as well. Man thats one big ass grow, 6000? Man I hate to see your light bill? LOL

Tryna

[trynagethigh]

If you can mount the fan in a wooden box of some sort, in other words contain the unit and try wrapping it in dynamat. its a sound deadener that is used mainly for trunks of cars to reduce the noise from high amped car audio.

Tryna

[farmerjz]

Thanks a lot folks for your kind replies. I appreciate the noise INSIDE is a consideration which I can deal with. My biggest concern is the roar of the air as it exits the window. Will a silencer on the o/p of a 1500 cfm fan reduce this so that folk behind windows 30 feet away will not be curious (or pissed off !).
I have the same problem but i solved it i have a furnace blower hooked up 2 my carbon air filter that exits the room im using dryer flex tube than attach 4" PVC piping i cut a 2 liter pop bottle in half and stuck this over 4 " PVC pipe with this its reduced 2 like 1 " this works awesome very very quiet noise reduction what size is ur piping ur u using look at my pics to see i have a small room so if ur using bigger piping u need to reduce the end pipe as small as u can

[farmerjz]

i 4got one pic this is the end with pop bottle cut in half the reduce the noise

[Garden Knowm]

HEY FARM,,,

doesn't that tiny opening cause your fan to work extra hard... and severly reduce its life?

cheers - nice picture

[houdini]

Thanks for the pics and your suggestions, Farmer. I have the same question as Garden Knowm - surely if you reduce the air output like that, the fan is going to be working like hell to push air through the small gap ? Garden Knowm, thanks for yr. advice. Tryna, my light bill is big, but its all relative, really :D

[babystarbud]

damm thats a big rig lol

cant really give advice, but the replies to this thread have given me a few ideas...

with somthing that size i would think you need to tackle the problem from a few angles...

the noise crated by the fan itself
dynamat is an exellent suggestion, used on the fan unit itself and/or any nearby hard surface to damp down the noise.

vibration from fan mountings/fixtures
rubber fixtures like bike tyres sound a great idea, also use rubber gaskets where any hard joints are made (screws/bolts) to isolate any vibrations as much as you can

exhaust exit and intake noise(air noise)

making the intake exit diameter smaller will indeed strain the fan bearings, maybe a sleved duct will help,if you have a 12 duct, fit a 13" duct over the top of it for some insulation and maybe fill the gap with pillow stuffing or some kind of spray-foam, although i think it dries hard so not too practical for mooving the duct around.

if you can vent into a wall cavity or loft space rather than directly outside it will also act as an acoustic barrier. a loft space full loft insulation will damp the noise down nicely, you could even line the apex of the roof as well as the loft floor.

thats about all i can thinkof lol

[trynagethigh]

That is exactly what is happening. By reducing the size of the exit point you are creating backpressure on the fan. Think about it in actuality you are bottlenecking the exhaust and will shorten the life of the fan itself. It also depends on how much space there is in your starting size and your end ruduced size. Naturally if you took a 10" fan and reduced it to a 4" in a matter of two feet, the fan is going to be struggling like a bitch to get the air out..somewhere..LOL. The fan itself also is working harder but no air is being passed through it to cool the motor. The fan relies on incoming air to cool it off as well.

Hope this helps.

Tryna

[bud bud ding ding]

get an inline fan that sits in your ducting and hang on rubber grommits.also you could get a larger fan and run it on a slow setting=less noise ORyou could get something called an acoustic fan which elminates exhaust noise altogether only prob is is there 300£ or 600$ but there so good.good luck

[farmerjz]

HEY FARM,,,

doesn't that tiny opening cause your fan to work extra hard... and severly reduce its life?

cheers - nice picture
i haven't really noticed never thought of it but its working 4 me that fan has been passed down a few times and still running Lol