Ventilation Disaster!

[Asterope]

Iv been building my studio and almost done (so at least i thought) :twitch:

The room size is 13.5' long, 11.5' wide and 6.5' tall. Luckily im short.
I installed a 12", 1050 cfm attic fan. Two 6" diameter holes for intake near back of wall on both side of room at ceiling.
So much vacuum is created and causes blowback from my exhaust fan, with or without the side of fan taped.
Also put variable speed on my fan but even at a very low speed im still getting vacuum and blowback.
When i open window all the way, the vacuum stops and the exhaust works properly
but then the air blowing in from the window pushes the fumes around from from the hood.

The room is already turning to swiss cheese and im not sure how much more intake i would have to create so the vacuum stops.
Any ideas would be grateful.
http://i173.photobucket.com/albums/w42/opiestuff/IMG_6897.jpg
http://i173.photobucket.com/albums/w42/opiestuff/IMG_6899.jpg
http://i173.photobucket.com/albums/w42/opiestuff/IMG_6900.jpg
http://i173.photobucket.com/albums/w42/opiestuff/IMG_6901.jpg

[LarryC]

No Surprise here. You have to supply some amount of make-up air from outside of the room to replace the air which you are exhausting.

[j4y]

You would loose your window but maybe build a duct through the window to redirect intake from the window away from your bench.?.?. If that makes any sense...

[Julian]

2 six inch free air intakes is definitely inadequate, as youve realized.

An opening the size of a window is good. A rule of thumb I've heard people suggest that 3 times the area of the output duct in free air is a good minimum.

[Bo Diddles]

Two six inch fans in the existing holes?

[hashmasta-kut]

ya that might do it good idea.

[boxfan willy]

roughly 5.1 cfm per square inch at equal static pressure on smaller diameter duct....and because you are not running insane linear ft. of duct. Larger diameter duct has less sp or resistance and can run closer to 7 cfm per square inch.

6" duct is radius, squared X pi
3 x 3 x 3.14= 28.26 square inches x 5.1 cfm = 144 cfm per 6" duct

Here are some general short run calculations from an HVAC site I reference...
4" Duct 40 cfm
5" duct 60 cfm
6" duct 100 cfm
7" duct 150 cfm
8" duct 200 cfm
9" duct 300 cfm
10" duct 400 cfm
12" duct 600 cfm
14" duct 900 cfm
16" duct 1,400 cfm
18" duct 1,800 cfm
20" duct 2,300 cfm.

[T-Rex]

I like Bo Diddle's idea... two small in-line fans will help push air in. Could be enough.

Boxfan Willy - what do those numbers mean... that for 900cfm free flow you need a 14" duct?

[elad65]

It's not necessary to power ventilation MAKE UP AIR. Your EXHAUST fan causes a low pressure area in studio (proper) outside air pressure forces air into partial vacuum. Simple rule here is "nature abhors a vacuum and will try to fill it." Keeping that in mind, your makeup air volume has to be equal to air you are exhausting. Room size is not a issue or important, amount of air you can move through room is important. Room is actually one large duct with a restriction on inlet and outlets (fan end of duct).

Example, if your exhaust fan is trying to move 1000 CFM your make up air has to be capable of providing 1000 CFM from its makeup opening.

Here is calculator I stumbled across to work with ventilation.

http://www.artglassanswers.com/calc2/test2.html

Also.

http://www.engineeringtoolbox.com/ventilation-systems-t_37.html
http://www.engineeringtoolbox.com/exhaust-hoods-d_1036.html

Also keep in mind this is not air conditioning ventilation where air is just circulated. IT is evacuation of toxic materials/gasses/particles/ heavy metals from fuming (CO and NOX) out of your breathing space to prevent respiratory illness from repeated exposure to toxins. NOX is nitrogen oxide from when "air" is superheated and the nitrogen in atmosphere is changed chemically and when combined with moisture is base for nitric acids you breathe the converted nitrogen (NOX) inters lungs and it combines with moisture in lungs and burns them---- Later in life you live on oxygen bottle because lungs have been irreparably harmed.

Venting on level we need is equal to and based on Class "A" fume cabinet used in industrial and scientific applications, not for comfort zones (room AC) . Do some research on industrial ventilation Mainly on "Class A" fume cabinets.

Also its not something just thrown together, it has to have a certain amount of design to insure it functions properly. Ideally one should have about 100 to 125 CFM of air flow for ever square foot of hood opening.

Elad

[boxfan willy]

Bo,

those are passive flow calculations. with that said, I do not think I have seen a 6" duct fan (http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?productId=202797339&storeId=10051&langId=-1&catalogId=10053&ci_sku=202797339&ci_kw={keyword}&kwd={keyword}&cm_mmc=shopping-_-googleads-_-pla-_-202797339&ci_gpa=pla#specifications) that pushed more than 350 cfm. Normally, forced air for make up creates turbulence in the system, but your make up ports are well placed, and shouldn't

Perhaps a couple of duct fans and a soffit vent (http://www.homedepot.com/webapp/catalog/servlet/Search?storeId=10051&langId=-1&catalogId=10053&keyword=soffit%20vent&Ns=None&Ntpr=1&Ntpc=1&selectedCatgry=SEARCH+ALL) in the bottom of your door.
Seems the window is positioned where it could push your flame around if you utilized it for make up air...

Nice looking build. Best of luck.

[wagon]

^ Yeah i agree. I think what boxfan is saying is that if the diameter of the ducting and the cfm of the fan don't match up properly, then it will throw off the static pressure of the entire room/system and possibly create the very issue you are having.




As for a diagnosis.
This issue could also be the caused if you have too much cfm for your entire system as a whole. Each system can only handle so much cfm before the air circulation in the room gets too crazy, then the whole system becomes one big vacuum.

Obviously, this can be prevented by having an intake with a larger area, big enough sq ft so that enough air can flow through to make up for the wild pressure while still maintaining a solid pressure in the system. We want a tiny bit of pressure, but not too much to avoid imploding our working area. A garage door cracked 1 panel off the ground (approx. 12") usually suffices. I usually do 1-2 panels, depending on how windy it is outside. Too big of an intake can cause issues as well so plan wisely.

Of course many of us don't have the luxury of a garage door in our studio, which causes this sp issue to arise often. I would consult a professional hvac company. They will help you understand everything if they're legit. Also, take a look at boxfans setup. Both combined helped me understand an insane amount about ventilation when designing my studio. mad respect. I feel safer than ever now.





As for a resolution to the problem.
Consider getting a speedster fan controller and to control the cfm until you find a cfm you like and then leave it dialed in to that setting. They're like $20 online. Your fan needs to be a 3 phase fan to work with the speedster. Calculate your fan cfm needs based on both the 125cfm per square ft of hood area basis, and the total size of your entire room. Each are equally important.

Make sure to take in to consideration that you want the air in the entire room to be bringing in fresh air every 3 to 5 minutes.

For Example. My garage is about 30ft W x 15ft L x 12ft H = 5400 cubic feet
My exhaust fan is a Vortex 12" 1140 cfm

5400 cubic feet/1140 cubic feet per minute = 4.736 minutes

4.736 minutes for my entire garage to circulate all of its air with a new fresh batch from the outside. Too much air moving around inside your system and you'll get the mini tornado effect (glass dust everywhere, even if we can't see I'm assuming), not enough air and you will regret lack of fresh air. Fresh air is your friend.






Also, remember that less diameter ducting than you need typically results in increased pressure around the suction area due to the venturi effect. (think of how a tapered nozzle attachment effects a vacuum suction when attached.) Flow is unchanged, the result is a different pressure.

It's important not to skimp out and to not use flex ducting just because it's cheaper. This decreases the cfms a lot. Same with bends, turns, etc. Make absolutely sure to use metal ducting. Make sure the ducts are sealed up really good with that pro hvac tape. Better safe than sorry when in a glass shop...

Another tip is to design the studio with your bench far away from the fresh air intake so there is a less chance of dust blowing around the studio or the intake distorting the flame characteristics.






Hope this information helps everyone. I struggled with this ventilation battle like everyone on here and want to help as many as I can with the info I have gathered.

Legit setup man. Looks solid. One Love

[boxfan willy]

that's it exactly. Creating a vacuum puts back pressure on your motor(which on an attic fan is already weakish) which will burn the motor out prematurely.

[Bo Diddles]

Vortex 6" fans are 450 CFM which would be close... But I really don't know much about ventilation. Just throwing that out there.

[Samson]

Looking at your third picture , should it have been my setup,I would have put a bigger fan dead in front of that window to the right, same "grainger" type style ...... that way you have the entire left wall to be your left box side ...... in front of you would be the pull (exhaust) .... then I would have built some sort of wall to my right creating a right hand box side, say 6 - 7 ft ... remember tube and rod come in 4 ft lengths ..... make a hood that touches both the left and right side and bam ...... you makeup air is coming from the left from the open door ..... the pull is happening from the huge fan in front of you .... and the sides controls all that unbalance you have ..... just my two cents, I've set up many, I think that would be your best bet. Peace and good luck

[Muse]

put your fan in the window, turn bench 90 degrees, leave door open. enjoy the view :D

[Asterope]

Thanks everyone for all the information.
I decided to build something to duct the airway coming in through the window on the right. Pretty much the easiest and cheapest way to go it seemed, j4y had the right idea going for my situation.
Problem solved! Repped for ideas and info.

http://i173.photobucket.com/albums/w42/opiestuff/IMG_6905.jpg

[somewhere]

that's it exactly. Creating a vacuum puts back pressure on your motor(which on an attic fan is already weakish) which will burn the motor out prematurely.

Just to expand on this. The reason the motor will burn out is because the fan will cavitate. No air to push the fan will speed up do to lack of air to move. In return the motor will run faster pull more amps and burn out. Think of it this way if you put your hand over the end of shop vac hose the motor speeds up you may think it would slow down but with no air move the motor spins faster (cavitation).