[labnetwork] Combined or separate exhaust?

[Dennis Schweiger]

Travis,

Good morning.  Here at the LNF, we have a single exhaust plenum that
provides exhaust across roughly 18,000 square feet of cleanroom, and
ancillary lab spaces.  This exhaust plenum is just a large box that has
six +25,000CFM strobic exhaust fans sitting on the top surface.  This
facility needs five of those six to remain operational, so once a month we
stop one, and ramp the standby unit up.  That way all of them see some run
time.  On this plenum module there are several large bleed-in dampers that
allow for the regulation of static pressure inside of the plenum (currently
7.5" of static).  In addition to the bleed-in dampers, there are isolation
dampers under each strobic fan that keep the air from returning through the
fan that is currently off.  Upstream of the exhaust plenum we have two
distinct exhaust systems in the fab.  One is for scrubbed exhaust
(supporting seven wet scrubbers) and is fabricated from PSP (Poly Shield
Pipe - internally teflon coated stainless steel), and the other is for
general/heat exhaust, and is fabricated from galvanized ductwork  This
system has been running since 2007 with only minor hiccups in operational
integrity.  The intent when we installed this system was to share the
redundancy of a single fan across multiple points of need , and to keep all
of our "contaminated exhaust air" system negative till it is outside of the
building.

Now with all that background, I must tell you that currently we're
running all six fans 24/7.  It seems that over time the pneumatic actuators
that modulate/isolate the various functions on the plenum have failed, as
have some of the damper mechanical assemblies due to their lack of
protection from the elements.  Later this spring, we will shut down the
exhaust system for a couple of days and do our first major overhaul  in 18
years, replacing all of the dampers (both bleed-n and isolation) and
replacing the pneumatic actuators with a mechanical screw type actuator.  I
haven't seen the final drawing submittal yet, so I'm not sure if the design
has addressed all of the shortcomings the current technology has in regard
to isolation from the elements. We're currently modulating the pressure in
the plenum manually by blanking off some of the bleed-in openings.  It's
not a difficult task, just a bit windy up there.

 I've attached a picture of our rooftop plenum to give you some idea of
arrangement, and location.

If you'd like to take a look at what we have, please feel free to give me a
call or stop by.  I'd be happy to share what we've learned.

Dennis Schweiger
University of Michigan
Lurie Nanofabrication Facility (LNF)
Ann Arbor, MI

734.647.2055 Ofc


On Tue, Feb 25, 2025 at 9:17 AM Massey, Travis <massey21 at llnl.gov> wrote:

> Hi all,
>
>
>
> LLNL is planning a significant cleanroom expansion, and the question arose
> whether we *need* separate exhaust for hoods and tools/gases, or if they
> can be combined into a single shared exhaust.  Or do you have a single
> exhaust with 2+ exhaust fans pulling simultaneously, so there’s always *some
> *exhaust air moving if one fan is down?  The conventional wisdom around
> here has its share of holes, so I’m out to learn from the broader nanofab
> cleanroom community.  How are your cleanrooms’ exhaust systems are
> configured, especially if you’ve had to go down this cleanroom design
> rabbit hole?
>
>
>
> I’m also broadly open *any* other lessons learned regarding provisioning
> exhaust or other utilities – whatever you feel like sharing.  Too much
> information during the design phase is far better than too little.
>
>
> Thanks,
>
> Travis Massey
>
> Center for Micro and Nano Technology (CMNT)
>
> Lawrence Livermore National Laboratory (LLNL)
> _______________________________________________
> labnetwork mailing list
> labnetwork at mtl.mit.edu
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