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Studio ventilation 101


#1

As a former practicing professional engineer, I want to convey some
important about studio safety regarding ventilation
systems. Previous to my metalsmithing career, I designed mechanical
systems for hospitals and labs - including the Mayo Clinic. I have
designed systems to exhaust everything from toxic chemicals to
aerosolized human tissue in operating rooms. Having read a number of
different posts here on Ganoksin about studio ventilation, I have
developed some guidelines that you can apply to create the best
system for your studio.

Unfortunately, most of the exhaust systems proposed for studios will
not function the way you want them to - i.e. get the fumes or
aerosolized debris out of your studio. In any type of studio
ventilation system, there are calculations that you can perform to
determine what the most effective solution is for your studio. I
think it may be short-sighted to rely on any manufacturer to give
you advice on what is best for your studio. Unfortunately, many of
those manufacturers are not engineers, and their goal may simply be
to sell you their system.

The most important thing to know about an exhaust system is that it
is dependent on these factors:

x = Distance of the exhaust intake from the source (ft)
vc= Capture Velocity (air flow in feet per minute)
q= Air flow in Cubic feet per minute (cfm)
vc = q/4(pi) (x2)

The further away the exhaust intake is from the source, the greater
the air volume you will need to get it to work effectively. This is
really important, because the volume of air required will very
quickly become something huge and unworkable for your home studio.
Here is an example:

Soldering

Target capture velocity = 200 fpm (feet per minute)

If the exhaust is 24"(2 ft) above my soldering bench, then the air
flow required would be

200=q/4(pi) (22)

q 0(4(pi) (22))= 10,053 cfm

I don’t have the ability to generate 10,000 cfm in airflow, or any
ability to make-up 10,000 cfm of air when my house becomes
negatively pressurized.

Since less distance means less air is required, I will try moving
the exhaust 1 foot closer:

200=q/4(pi) (12)

q=2513 cfm 2,500 cfm is still a huge amount of airflow for any home
studio

As you can see, it’s not a simple thing to get any kind of effective
exhaust system in a home studio. Even if you were able to buy a
system that generated 2,513 cfm of negative airflow for you studio,
you would have the instant problem of more air out than in,
requiring make-up air. If you were able to put in a supplementary
air flow system for make-up air, you would then face the problem of
re-heat for that make-up air so that you could work comfortably.

The most effective system for a home studio is a self-contained sash
hood. Whatever process you are doing would then be done inside the
hood workspace with the sash hood closed as much as possible. I know
there are sash fume hoods occasionally on Craig’s list or Ebay.
However, this is an expensive solution that won’t help the average
metalsmith with a home studio.

To give you an idea of the range of target face velocity’s for
different activities performed in our studios:

Soldering 100-200 fpm
Grinding 600-2000 fpm
Chemicals 200-400 fpm

For a home studio, the best we can do is to approximate the exhaust
performance, meaning create the best system for the least amount of
money, i.e. the highest reasonable negative airflow for a
residential application. The most important aspect that you can
control is the distance of your exhaust from the source. The less
distance the better. This means inches away, not feet. The best is a
self-contained hood with a sash.

If you currently have some kind of exhaust system in your studio
consider a few modifications:

Shorten the distance between what you are doing and your exhaust
source.

Increase the face velocity of your system by blanking off part of
the face with sheet metal, thus increasing the face velocity.

I want to finish here with a note about filtration. Contrary to some
posts I have noticed, filtration serves no purpose here. You are not
(and should not!) be re-circulating exhaust back into your studio.
You do not need to filter what you are exhausting. Kitchen exhaust
hoods have grease filters because grease in ductwork is fuel for
fire. If you want to be very technical, you can run your exhaust
system to your roof, but that will require higher air flow to
overcome the pressure loss.

As metalsmiths, we work with a lot of hazardous materials -
soldering fumes, acids, chemicals, kiln exhaust, sanding, grinding
and polishing to name a few. Give some careful consideration to how
you can best protect yourself from exposure by installing an
effective exhaust system.

Sincerely.
Gwen Bernecker, PE
Two Olives Studio
http://www.twoolivesstudio.com


#2
If you want to be very technical, you can run your exhaust system
to your roof, but that will require higher air flow to overcome the
pressure loss. 

Are you saying a vertical exhaust is better?