[labnetwork] Specification for clean dry air (CDA)

[Robert M. HAMILTON]

Labnetwork Colleagues,

I recently contacted Dennis Grimard eho is helping design and build MIT's
new lab to learn their specification for their compressed dry air (CDA).
Dennis is terrific with numbers and engineering data. Dennis suggested it
might be useful to broaden my query to the labnetwork. This begs the
questions, how do other facilities specify their CDA and who supports their
systems?

At the outset I’ll comment many university labs use their campus
engineering maintenance support to service utilities and specs may not be
at one’s finger tips. And, some universities have central plants for
utilities which serve a broad number of facilities. In the case of the
Marvell NanoLab we have virtually all our utilities contained within our
sub-fab and we have chosen to maintain most utilities e.g. our acid waste
neutralization system, air handlers CDA, DI water, LN and process cooling
water system because we are so dependent on them.

My question is what are reasonable specifications for CDA? I realize this
is a difficult question to answer because CDA usage will be based on an
equipment load.  Perhaps adding a labs square footage helps to scale an
answer?

The UC Berkeley Marvell NanoFabrication lab’s CDA is derived from two Atlas
Copco 117 cfm (3,32M^3/min) screw compressors operating in a lead/lag
configuration which deliver to a 200 gallon storage vessel, then to an
Air-Tak brand dryer and Zander particle filters before delivery to the lab.
Our CDA delivery specification is 90 psi at a dewpoint of -70F (~16 ppm
H2O). We began with a dewpoint spec of -90F; however, we relaxed this spec.
to reduce the work of the air dryer with wearable, moving parts. As backup,
to facilitate the orderly shutdown of equipment and for brief periods to do
CDA system maintenance our delivery is configured to automatically cross
over to the lab’s cryogenically derived process N2 when the pressure falls
below 70 psi. Such a crossover can support the lab for several hours using
N2; however, the associated LN vessel vaporizers do not have sufficient
capacity to run on cryogenically-derived N2 for extended periods of time –
they ice over.

As has been previously noted, a few years ago we substituted CDA for N2
purging on a select number of dry pumps to reduce our N2 costs. The pumps
switched to CDA were pumps which service equipment that does not pump
acid-gases, flammables or pyrophorics. This has been a great success. The
downside; however, is we are now peaking our CDA demands to greater than a
single compressor can sustain. This makes us vulnerable should we lose a
compressor.

Comparing how various research fabs spec CDA has value.

Regards,
Bob Hamilton


Robert Hamilton
University of CA, Berkeley
Marvell NanoLab Equipment Manager
Rm 520 Sutardja Dai Hall, MC 1754
Berkeley, CA 94720
Phone 510-809-8618 (desk - preferred)
Mobile 510-325-7557 (my personal mobile)
E-mail preferred: bob at eecs.berkeley.edu
http://nanolab.berkeley.edu/
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