Does my ventilation look OK?

beakillion · #1 2013-02-11, 12:39pm

The shed is 10x16. The table is opposite (on an angle) the door and the shed has 4 windows. The inline fan is 700 cfm but I'm not sure if it is the right kind, but it's up already, so can't do anything about it. The hood is 20x14. That's all we could find. I'm just concerned about the makeup air from the door and window, it's less than 10' from the actual exhaust fan.

houptdavid · #2 2013-02-11, 12:51pm

The 10' rule is more if the vent and makeup air are on the same wall, since you vent out the roof it should be fine. I would consider adding a makeup air vent under your bench

beakillion · #3 2013-02-11, 12:55pm

What does the vent look like? Is it just a hole in the shed (wall) under the table? Or does it have some kind of fan attached to it?

houptdavid · #4 2013-02-11, 2:05pm

Pretty much, ducted up to the bench, no fan!

beakillion · #5 2013-02-11, 3:24pm

thank you

Alaska · #6 2013-02-11, 4:43pm

Give your system the smoke test. Sit at the bench with the torch on and hold a smoking piece of wood or incense stick by your head and see if the smoke is drawn up the stack.

Dale M. · #7 2013-02-11, 7:40pm

Ahem.... The poster states there is a 700cfm inline fan in system... Why does everyone assume its a convection system....

And yes a smoke test will tell you if its "functional" or not.....

Dale

beakillion · #8 2013-02-12, 6:39am

I did an incense test and it does goes right up into the hood with fan on. So I guess it's alright. Just sometimes the flame moves, But I don't know if it's the fan or the open door. Or both.

RSimmons · #9 2013-02-13, 6:52am

For smoke testing these matches are far better than incence. It's a small investment in a better way to check things out.

http://inspectusa.com/second-smoke-e...ar-p-1631.html

I use a powered duct to bring make up air in through my bench top. It helps keep condtioned air in the room during weather extremes. I still have some flow over my shoulders but most of the torch plume goes up the hood carried by the air coming in under the table.

Robert

beakillion · #10 2013-02-13, 8:28am

Thanks for the information. I was wondering how far away are you supposed to hold the incense or smoke thing from the hood? I think I held it about a foot away from the hood, and the smoke was drawn up the hood. Was this enough or are you supposed to hold it out further? I tried searching the site to find answers, but I just keep reading about doing the "smoke test".

RSimmons · #11 2013-02-13, 11:16am

One good test is to sit down at your torch, light it, and then run the smoke match around in the area where you are sitting, especially in front of you. This simulates working conditions. You also can see if you are creating a low pressure zone in front of your body which may draw fumes back towards your face.

Robert

Imaglassgal · #12 2013-02-13, 1:12pm

Quote:

Originally Posted by RSimmons

One good test is to sit down at your torch, light it, and then run the smoke match around in the area where you are sitting, especially in front of you. This simulates working conditions. You also can see if you are creating a low pressure zone in front of your body which may draw fumes back towards your face.

Robert

That low pressure zone thing is exactly what I'm having trouble with. My HVAC guy is stumped. Any hints as to how to redirect the airflow to overcome this problem?

Alaska · #13 2013-02-13, 6:10pm

In some range hood applications for lampwork one possible design is to use something like the attached. A good HVAC firm should be able to design a baffle that would work for your application. The attached is only a demonstration of one type of baffle and is is not intended for use in your application.

Maui Greenstone · #14 2013-02-13, 9:18pm

Here is a link to the ventilation 101 thread over at talkglass. I think 700 cfm is pretty weak. I personally would bump it to over 1000 ideally 1500. But yeah this link will tell you more than you want to know about ventilation

http://www.talkglass.com/forum/showt...entilation-101

Dale M. · #15 2013-02-14, 7:56am

Another link to ventilation information...

http://www.artglassanswers.com/forum...php?f=12&t=273
http://www.artglassanswers.com/forum...659b1d2c8e311d

Dale

philomena · #16 2013-02-17, 1:04pm

Quote:

Originally Posted by RSimmons

You also can see if you are creating a low pressure zone in front of your body which may draw fumes back towards your face.

Robert

I need to come back to this point.
How does this low pressure zone come? I always have the feeling when I'm sitting on my torch the fumes come back to my face. But I have to apologize, I have never heard of a low pressure zone. What is the theory behind it?

I really read a lot about how a ventilation set up should look like for beadmaking and in my class with Loren stump we discussed a lot about it. Everybody said my set up seems to be fine but I always complained about my feeling the fumes are coming back to me.

It would be a big help for me to know what I have to change.

Cheers
Kathrin

beakillion · #17 2013-02-17, 3:08pm

Kathrin, I have the same feeling that the fumes are coming back to my face also. We just put sheet metal around the hood. From the hood to the back wall and down the sides, and a baffle on the front of the hood and when I tried out the hot head torch, I feel the hot air heat from the hot head coming towards my face. Then yesterday I tried putting a fan behind me blowing towards my head and that seemed to help as long as I didn't lean too close to the torch. I haven't tried it with the minor torch yet. It seems no matter what we do, something doesn't feel right..

Alaska · #18 2013-02-17, 11:19pm

Take one ply of a 2 ply Kleenex about 1 inch in width. Hold in various places with fan on and torch off to see how much air movement there is.

RSimmons · #19 2013-02-18, 6:42am

When you have a fluid flowing past a fixed object you will observe a swirling into the space behind the object. A vacuum of sorts (low pressure) forms behind the fixed object and draws the fluid back into the space behind it. You can see this if you fill your tub with water and then move your hand through the water in one direction. You will see cavitation behind your hand and swirling currents in the water moving back towards your hand, the faster you move the more this will occur. This happens when you sit in the air flow going past you into your hood. Air will swirl around into the space in front of your body and can pull some of the torch exhaust back with it. Much of the heat you may be feeling is radiant heat from the flame and glass in it. A smoke test will show you if you are pulling torch exhaust into the area where you are breathing.

If this happening you may need to change where you sit relative to the torch (back a little will help), check that your air flow rate is such that it clears your torch plume but isn't strong enough to create this zone in front of your face that pulls in air from directly above the flame. I use makeup air coming in from under the table in front of the torch and it reduces the turbulence when I am in front of the torch by reducing the amount of air flow coming around my body.

Robert

Quote:

Originally Posted by philomena

I need to come back to this point.
How does this low pressure zone come? I always have the feeling when I'm sitting on my torch the fumes come back to my face. But I have to apologize, I have never heard of a low pressure zone. What is the theory behind it?

I really read a lot about how a ventilation set up should look like for beadmaking and in my class with Loren stump we discussed a lot about it. Everybody said my set up seems to be fine but I always complained about my feeling the fumes are coming back to me.

It would be a big help for me to know what I have to change.

Cheers
Kathrin

beakillion · #20 2013-02-18, 10:25am

We put sheet metal around hood. From the rear top of the hood to the wall and down the sides and triangle pieces on the sides of the hood. But I don't know if this is good because there is more of a box in the rear and not so much on the sides. The hood itself only measures 20wx14deep. From the front of the hood to the back wall is about 30".That's just metal tape in the front for a baffle. ( I know it's pretty bad looking)!

philomena · #21 2013-02-18, 12:14pm

Thank you for your answers and pictures!

Now I understand how the low pressure zone occures and how to prevent it.
Tomorrow I will test and see what I can change.

Thanx
Kathrin

Dale M. · #22 2013-02-18, 4:07pm

Quote:

Originally Posted by beakillion

We put sheet metal around hood. From the rear top of the hood to the wall and down the sides and triangle pieces on the sides of the hood. But I don't know if this is good because there is more of a box in the rear and not so much on the sides. The hood itself only measures 20wx14deep. From the front of the hood to the back wall is about 30".That's just metal tape in the front for a baffle. ( I know it's pretty bad looking)!

Should only improve airflow around you and better to pull unwanted gasses up vent.... Would be even better if actual suction port was back closer to wall....

Dale

beakillion · #23 2013-02-18, 6:56pm

Thanks Dale for you knowledge and help.