Studio ventilation question...

[Cosmo]

We are in the process of building a studio that will have an 8-torch setup. Is there a formula to determine how big of a fan we need for ventilation? We haven't built anything yet. We're still in the planning stages. But, if I know the daimeter and length of the exhaust piping, is there a way to determine how much exhaust flow I need?

[MikeAurelius]

No - it doesn't really work that way. The size of the fan is dependant on how big the hood is.

For an overhead hood in the center of the room, you are going to need about 125 CFM per square foot of hood coverage.

I assume you are going to use a table or two tables side by side to mount the torches on, correct? Let's assume you are going to use 2 tables, each table measures 5 feet by 2 feet, so the total table area will be 5 feet by 4 feet, or 20 square feet. Multiply 20 by 125, and you get 2500 CFM.

You can run the fan(s) several ways, for example, you can use one 2500 CFM fan or two 1250 CFM fans, or three 850 CFM fans.

With a hood of this size, you might want to consider two or more fans, just so that if one or more workstations are not being used, you can essentially "turn off" one entire section of the hood and not have to worry about exhausting 2500 CFM of air for just a couple of torches.

You could use a variable speed motor control, but I don't recommend them for use with a multi station vent hood arrangement, only for one fan running a multi hood arrangement, similar to what I have at MAGiC.

[Cosmo]

Well, what I was thinking is running individual piping to each torch. I've seen studios set up like that, but I can't find the photos I was thinking of. Is there an advantage to running a big hood over running individual vents? I believe the cost won't be much different either way. One of the owners if the building is a contractor, so he has basically told me to just tell him what I need and he'll get it.

The idea of a large hood does seem easier to fabricate, though.

[MikeAurelius]

You mean an open duct behind the torch? No - not a good idea. You may trap "some" of the exhaust plume, but you don't get all of it, and if there are other things being done, such as frit or fuming, an open duct won't capture any of the frit dust or fume vapors.

It is far better to use either a single overhead hood or individual workstation hoods/enclosures.

Large hoods do have thier drawbacks, for example the amount of air exhausted also needs to be replaced and if you are in an area with weather extremes, the incoming fresh air will probably need to be tempered (warmed or cooled) prior to being brought into the studio.

My personal preference is for individual workstation enclosures, although this is not a perfect solution, especially if the worker is making large pieces or works with long tubing parts.

[InspirationToolworks]

Mike, a question on hood design...

You say that a open duct behind the torch won't get all of it. Do you know how big a duct needs to be before it catches enough of it?

It would seem if we are talking only about combustion products and fumes from the heating that it should be possible to have an opening big enough (and fast enough) to get all of it.

I'm asking becuase we have a situation where either an overhead or a full size box would be a PITA.

Thanks!

-Jeff

[MikeAurelius]

There is no good size to do that, Jeff. The duct basically has to be above and behind the torch plume to catch all of it.

The biggest problem with an open duct style of trap (I won't call it a hood) is that it requires a lot of CFM's in order to suck the stray fumes into the ducting - probably twice what a conventional style overhead or workstation hood would require.

[InspirationToolworks]

So.... if it is above and behind, and has a large CFM, it would be okay, but not as good as one would like?

Thanks!

-Jeff

[Cosmo]

Okay, here's another question about my setup...

Does it matter if the fan is on the hood side of the ductwork? What I'm asking is, can we put the fan at the wall/ceiling where the exhaust is blown out, so it sucks through the ductwork, instead of right over our heads at the hood?

[MikeAurelius]

No - noise only. It's usually better to have the fan as far away from your workstation to keep the noise factor down.