Steve,

ETS is a reflow manufacturer so we deal with exhaust problems all the time
and even started selling exhausting equipment in order to assist customers
ensure proper exhausting. Exhausting is a very critical part of the reflow
process and can affect temp uniformity.

One thing I thought of while reading your e-mail is that each machine
specifies required exhausting AT THE MACHINE. It should also state the
static pressure. For example, the CUREFLOW oven requires 400cfm at 1" static
pressure at the oven. Duct size (not to mention elblows and such) will
affect flow at the machines. You exhaust blower does sound close to adequate
but you will need to take flow readings at the machines. You also will need
dampers at the machines which will precisely regulate flows. 

You also mention that your exhaust system has pulleys. Can you put bigger
pulleys on to get more cfm's? If you do end up needing to replace the blower
make sure you install another exhaust controller with pulleys so that
exhausting can be increased in the future but first look into buying bigger
pulleys for the existing roof unit.

I could help more if you would like to call me or continue the discussion
offline.

Brian Stumm
ETS, LLC
509-483-0900 (voice)
509-483-0331 (fax)
[log in to unmask]

>Hello Technetters!
>
>     I've got a problem that hopefully somebody can teach me a little
> something about. It has to do with exhaust requirements and our Trek Triton IV
> that we'll be getting in a week or so…(at least I got that make-up DI water
> issue taken care of...thanks to all of you!
>
>     The next problem is; I just got the quote for the exhaust duct-work that
> I need to get done, I gave it to my boss, who then promptly had a cow.
>
>     What the moo'ing was all about is that the quote is around 11K. Both he
> and I are having a hard time understanding why the company is quoting us a new
> exhaust fan to replace the one we already have up on the roof...and yes, it's
> still there after the day before yesterday (we're in Sunnyvale, California
> about a mile or two from where the tornado was).
>
>     I should probably describe what I currently have, what equipment I'm
> going to be exhausting, and what the quote is actually for.
>
>     I wanted to exhaust 4 machines from one exhaust fan up on the roof. There
> will be a Heller 1700 convection oven which the specs say I need 500 cfm, a
> Soltec Prisma wave solder (I can't remember what kinda' suck it needs, the
> spec is on my desk at work), a waste water evaporator coming off a ultrasonic
> stencil cleaner (which has it's own exhaust blower rated at 1600 cfm so it
> really won't add a whole lotta load), and last but not least our Trek
> Triton...and that seems to be the culprit behind the big buck expenses.
>
>     Trek spec's say that it needs a -1.5 in. hg. negative pressure in the
> duct, the HVAC company that quoted us says the fan we currently have doesn't
> suck enough, but I think it sucks pretty good. They want to completely replace
> the fan we have which means a crane rental, and cutting a different hole in
> the roof with all the associated work that goes along with that.
>
>     Before we had the company quote our duct work, me and our facilities guy
> checked to see how much the fan we have sucks. We went up on the roof and
> checked to see what kind of unit we had. It's a Dayton unit, so we checked
> with Grangers (they sell Dayton), and based on a 2-hp, 1725-rpm motor with a
> 3.5" dia. pulley, and a 24.5" centrifugal ventilator type fan with a 9"
> pulley, they said we would get around 5700 cfm which we thought was plenty,
> but they never mentioned anything about negative pressure...we didn't ask
> though', I was mainly concerned about cfm until I was told that the fan needed
> to be replaced.
>
>     This is the first time I've been aware of a negative pressure requirement
> inside the exhaust duct of any equipment that I've worked with...but I only
> know enough about ducts and exhaust fans to be dangerous. I know that if the
> exhaust system isn't set up correctly, you can have all kinds of process
> problems, that's about it.
>
>     The company that was in this building before us, left the exhaust fan and
> a good portion of the duct work up, and they were exhausting 4 reflow ovens, 2
> wave solders, and a ultrasonic stencil cleaner evaporator. I know that because
> we found a layout drawing of the production floor they had, plus I also knew
> some of the people who worked for the company that was here. So that's adding
> to my confusion of why we need a different type of exhaust fan.
>
>     The only horizontal duct runs from the main manifold will be to the wave
> and the reflow, the moisture laden exhaust from the cleaner and evaporator
> will be making more or less a straight shot up through the roof as they will
> be located beneath the exhaust fan...that much I know about, you don't want
> any chance for the moisture to re-condense inside the duct and start
> collecting there, or to start to run back inside the machines.
>
>     So what am I missing? I've kinda' heard that this could be the case of a
> union shop just charging us way too much, but like I said, I'm not a guru on
> this stuff. Can anybody enlighten me?
>
>                               Thanks again!!!
>
>                              -Steve Gregory-
>
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