Barley Box Fan

Kay · #1 2012-08-18, 11:35am

Hi Everyone.
First of all I am new to lampwork and currently taking classes. I have been lurking here awhile to learn as much as I can about safety in setting up my own studio. (Thanks for all the great info you've all contributed here!!) I'm going to be torching with natural gas and an oxygen concentrator. I've built my barley box, read the recommendations about rigid duct work, fewest turns possible, shortest duct possible, and I found the formula and know the CFM requirements for my fan. So here is my question -- I have only really seen people venting out of the top of their barley boxes. I don't think I saw any examples where the fan was pulling air from the side or the back of the box. In my setup, the advantage to venting from the side or the back is getting the air out of my barley box a bit faster (1 less angle and a couple feet shorter). Does anyone know if ducting out the side or back of my box would work? Would the fan distort the flame? Hope this makes sense. Thanks for any insight! Kaya

Dale M. · #2 2012-08-18, 11:55am

Most people take it out the top because its easier to get it out and away from top.... Also from top because convection causes gasses to rise so you are pulling from highest point.... And it usually pulls flame straight back and up.... Not to side....

But there is really no reason from side will not work, as long as "fume cabinet" (what it really is in science and research and industrial world) does not have to much turbulence (causes flame to pull or dance) and it evacuates harmful combustion byproducts and heavy metals out of cabinet...

Dale

Kay · #3 2012-08-18, 2:06pm

...Which completely makes sense. So my choices are a) vent out the top, grab the maximum bad air, and have 2 angles in my duct or b) vent out the side, maybe missing some of the bad stuff, and shoot right outside with no angles. Do you have an opinion which would be the safest option? Thanks!

houptdavid · #4 2012-08-19, 9:02am

If you use a "squirrel" cage in a plenum , and vent out the top, and straight out the wall, you will have NO bends in your duct work

artsyuno · #5 2012-08-19, 10:14am

Can you vent out the top end of the back? I'd be a little worried about venting out the side, because the fan may pull your flame to the side.

Kay · #6 2012-08-19, 10:48am

Thanks David. The issue is height. I'll have to cut a hole in my brick home -- don't want to do that at just any random place. So lower is better (i.e. behind bushes). Venting out the top means ducting over and down to an appropriate height. I'm going to upload a pic (attempting!!) to show you what I mean. Thanks. Kaya

RSimmons · #7 2012-08-19, 2:31pm

Pulling air from the bottom will not help with the hot exhaust that will collect in the top part of your box. I would pull from the top and use either the vacuum plenum mentioned by David or get a strong enough blower to cope with the bends.

Robert

Kay · #8 2012-08-19, 3:22pm

Thanks for the input. I'm going to come out the top with a stronger fan since I have to force the exhaust down. I like this idea better anyway so I don't have to be concerned about pulling the flame to the side. I'm also going to hinge a piece of plexiglass across the front. It will come down about 12 inches -- hinged so I can easily get in there as needed. Thanks you all -- I only got this far because of all your previous posts.

Dale M. · #9 2012-08-19, 6:35pm

If you bring down a piece of Plexiglas, you reduce the face opening of fume cabinet, there for you can reduce fan size....

Dale

Kay · #10 2012-08-20, 5:10am

Hey Dale, does that still apply even if I have to force the air down through the duct? With the plexiglass, my opening is 3ft wide x 2ft deep. Depending if you use 100 or 125 in the formula, my fan needs to move between 600-750 CFM. I was going to purchase a Vortex VTX1000 10" (790 CFM) to account for the ductwork moving down. You think that is overkill, underkill, or just right? If 8" is sufficient I could get the smaller Vortex VTX800 8" (747 CFM). Thanks...

Dale M. · #11 2012-08-20, 6:20am

Any short duct run is not going to make real difference in fan performance... The killer would be to small of duct diameter... Air does no care whether it flows up or down or side ways... What matters is duct diameter, number of turns and total length of run, its really all about friction and turbulence in duct.... If run is short then diameter is only real thing to consider...

A 750 CFM fan would probably be sufficient... There is generally a little wiggle room here...

And face opening is measured by height and width, not height and depth...

Dale

Kay · #12 2012-08-21, 1:02pm

Thank you again Dale, and others as well.