Steve,
Give me a call later this afternoon.
Fred Golisano
[log in to unmask]
(408) 557-7039
______________________________ Reply Separator _________________________________
Subject: [TN] ASSY: Exhaust Fans, Ducting, and suck power...
Author: "TechNet E-Mail Forum." <[log in to unmask]>, at corp
Date: 5/6/98 6:05 AM
Hello Technetters!
I've got a problem that hopefully somebody can teach me a little=0As=
omething about. It has to do with exhaust requirements and our Trek Trito=
n IV=0Athat we'll be getting in a week or so=85(at least I got that make-=
up DI water=0Aissue taken care of...thanks to all of you!
The next problem is; I just got the quote for the exhaust duct-work =
that=0AI 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=0Aand I are having a hard time understanding why the company is quoti=
ng us a new=0Aexhaust fan to replace the one we already have up on the ro=
of...and yes, it's=0Astill there after the day before yesterday (we're in=
Sunnyvale, California=0Aabout a mile or two from where the tornado was).=
I should probably describe what I currently have, what equipment I'm=
=0Agoing 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=0Awill be a Heller 1700 convection oven which the specs say I need =
500 cfm, a=0ASoltec Prisma wave solder (I can't remember what kinda' suck=
it needs, the=0Aspec is on my desk at work), a waste water evaporator co=
ming off a ultrasonic=0Astencil cleaner (which has it's own exhaust blowe=
r rated at 1600 cfm so it=0Areally won't add a whole lotta load), and las=
t but not least our Trek=0ATriton...and that seems to be the culprit behi=
nd the big buck expenses.
Trek spec's say that it needs a -1.5 in. hg. negative pressure in th=
e=0Aduct, the HVAC company that quoted us says the fan we currently have =
doesn't=0Asuck enough, but I think it sucks pretty good. They want to com=
pletely replace=0Athe fan we have which means a crane rental, and cutting=
a different hole in=0Athe roof with all the associated work that goes al=
ong with that.
Before we had the company quote our duct work, me and our facilities=
guy=0Achecked to see how much the fan we have sucks. We went up on the r=
oof and=0Achecked to see what kind of unit we had. It's a Dayton unit, so=
we checked=0Awith Grangers (they sell Dayton), and based on a 2-hp, 1725=
-rpm motor with a=0A3.5" dia. pulley, and a 24.5" centrifugal ventilator =
type fan with a 9"=0Apulley, they said we would get around 5700 cfm which=
we thought was plenty,=0Abut they never mentioned anything about negativ=
e pressure...we didn't ask=0Athough', I was mainly concerned about cfm un=
til I was told that the fan needed=0Ato be replaced.
This is the first time I've been aware of a negative pressure requir=
ement=0Ainside the exhaust duct of any equipment that I've worked with...=
but I only=0Aknow enough about ducts and exhaust fans to be dangerous. I =
know that if the=0Aexhaust system isn't set up correctly, you can have al=
l kinds of process=0Aproblems, that's about it.
The company that was in this building before us, left the exhaust fa=
n and=0Aa good portion of the duct work up, and they were exhausting 4 re=
flow ovens, 2=0Awave solders, and a ultrasonic stencil cleaner evaporator=
. I know that because=0Awe found a layout drawing of the production floor=
they had, plus I also knew=0Asome of the people who worked for the compa=
ny that was here. So that's adding=0Ato my confusion of why we need a dif=
ferent type of exhaust fan.
The only horizontal duct runs from the main manifold will be to the =
wave=0Aand the reflow, the moisture laden exhaust from the cleaner and ev=
aporator=0Awill be making more or less a straight shot up through the roo=
f as they will=0Abe located beneath the exhaust fan...that much I know ab=
out, you don't want=0Aany chance for the moisture to re-condense inside t=
he duct and start=0Acollecting 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=0Aunion shop just charging us way too much, but like I said, I'm not=
a guru on=0Athis stuff. Can anybody enlighten me?
Thanks again!!!
-Steve Gregory-
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