[labnetwork] FW: Temperature specification for facility process chilled water
Vito Logiudice
vito.logiudice at uwaterloo.ca
Mon Sep 21 10:33:48 EDT 2015
Thank you all for taking the time to share so many great insights and experiences.
In my experience running PCW at a set point anywhere from 17C to 18C is usually acceptable for most tools. We’ve run as high as 20C when faced with some desperate conditions at our temporary facility a few years ago and did not see any obvious issues at that time. I share Peter J. Duda’s concerns about condensation but so far running at no less than 15.4C or so (at worst) has not given rise to any issues in any of the past four seasons.
In our particular case, the cleanroom PCW loop is CPVC and it has its own dedicated heat exchanger, filters and primary & backup pumps. However, the water (set & maintained to a conductivity of 20 microsiemens) is shared with the rest of the building with all of it flowing back common to a large, common reservoir (this is an open-loop system with near-zero back pressure on the returns). For a variety of reasons which I am open to discuss over a beer one day, SS was used throughout the rest of the building. What has made matters difficult here is that many of the labs to which the water is distributed have since been fitted with copper pipes. We are seeing minor signs of corrosion of these particular pipes likely due to galvanic effects and the water’s resistivity. No major issues have been noted in our facility or any of the labs so far but this is the sort of thing that sometimes keeps me up at night.
Best,
Vito
--
Vito Logiudice P.Eng.
Director of Operations, Quantum NanoFab
University of Waterloo
Lazaridis QNC 1207
200 University Avenue West
Waterloo, ON Canada N2L 3G1
Tel.: (519) 888-4567 ext. 38703
Email: vito.logiudice at uwaterloo.ca<mailto:vito.logiudice at uwaterloo.ca>
Website: https://fab.qnc.uwaterloo.ca
From: Rizik <rizik at intengr.com<mailto:rizik at intengr.com>>
Date: Friday, September 18, 2015 at 3:38 PM
To: Bill Flounders <bill at eecs.berkeley.edu<mailto:bill at eecs.berkeley.edu>>
Cc: "labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>" <labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>>
Subject: Re: [labnetwork] FW: Temperature specification for facility process chilled water
Bill and Tim,
Please let me chime in here. Over the past 32 year designing, building and operating PCW systems at various high tech facilities here are my thoughts:
1. Temperature control: tighter temp control range could be easily achieved by using a "Modulating V-Port control ball valves with pneumatic actuators" compared to other types of control valves as long as you have a relatively stable CHWS temperature.
2. Bacteria control:
a) open loop: usually such a system includes a storage tank equipped with nitrogen purge to minimize CO2 absorption, hence very low or no bacteria growth. PCW tanks that don't have nitrogen purge will develop bacteria and biofilm growth on the piping surface.
b) closed loop: closed loop systems filled with RO water don't experience frequent bacteria growth. Sterilizing the system once every couple of years then refilling with RO water is recommended. You can also add a biocide but it will defeat the purpose if you need to maintain resistivity at a certain level. However, bacteria growth could be better controlled by adding a bacteria UV light in a side stream connected between pumps' discharge then back to the PCWR pipe upstream of the air separator snd pumps suction.
3. Resistivity control:
a) open loop: as Bill stated this is usually achieved by the bleed and feed method. DI water is added to the tank when water resistivity drops below a preset level. Excess water overflows from the tank to the AWN. This method uses more water and takes longer to raise resistivity to the preset level. A more effective way is to bleed PCW from the PCWR pipe by activating a side stream solenoid valve then adding DIW to the tank until the desired resistivity level is achieved. This will take less water and time to achieve the preset resistivity level.
Another way to control open loop and closed loop resistivity is by running a PCW side stream from the pumps' discharge into ion exchange beds then return the water back to the tank or pump suction respectively. Adding a bacteria sterilizing UV light to this side stream will
Be an economical way for controlling bacteria growth in the PCW system.
15 years ago we were invited by Novellus to evaluate their open loop PCW system which developed very high bacteria levels due to the absence of nitrogen purge. Prior to our involvement Novellus attempted to sterilize the system using sodium hypochlorite. Unfortunately they ended up destroying the phosphating layer on the interior surface of the vacuum pumps and causing them to rust. Adding pain to misery the system developed iron eating bacteria which resulted in destroying their vacuum pumps which had to be replaced at $54K a piece.
In conclusion, depending on the system that you currently have you can design and install one or a combination of the features described above that will serve your needs. Please feel free to call or write back for any questions.
Regards
Rizik Michael
Cell: 408 718 0927
Sent from my iPhone
On Sep 17, 2015, at 7:59 PM, Bill Flounders <bill at eecs.berkeley.edu<mailto:bill at eecs.berkeley.edu>> wrote:
No biocide or corrosion inhibitors on the pcw loop.
Piping is copper. 306 SS was rejected for cost savings.
CPVC would have been preferred and additional cost
savings but initial code interpretation would not allow CPVC
since it does not meet 25/50 smoke/flame spread requirement.
Resistivity target is 200kohm.
At 175k, tank dumps ~20% system volume and is refilled with RO.
Resistivity recovers to ~275k. System resistivity gradually decreases
over 3-5 days and cycle repeats. Recurring fresh water input is what
avoids need for biocide or inhibitor.
If any failure of pcw pump/flow - system automatically crosses over
to single pass ICW. Resistivity spec is bypassed. When PCW flow
is restored, resistivity control is reimplemented and 4-5 tank dumps
required to restore system to normal. A picture is worth 1000 words:
Appended graph summarizes resistivity as function of time for the
past 1month. 2 cross over events to ICW are noted.
Bill Flounders
UC Berkeley
<PCW_Resistivity.jpg>
Miller, Timothy J wrote:
Iain,
Normally Jeff Kuhn would answer this, but he is out this week on family business.
All of the components in our PCW system are stainless steel, CPVC, or fiberglass. We haven't really worried about corrosion preventers since the building was commissioned.
In ten years of operation we have had one problem with bacteria. The system was dosed once with biocide, which was then removed by dilution.
No UV sterilizers or mixed beds. If there is a catastrophic loss of water we can refill from the RO on the UPW system, which runs 1-2 MegOhmcm. If the resistivity of the water drops below .95 Meg the system is topped off with concentrate water from the ultrafilters on the UPW system (18.2 Meg) with the excess water overflowing to drain until the resistivity returns to 1.05 Meg. Very simple and very inexpensive.
Tim
Timothy J. Miller
Purdue University
Birck Nanotechnology Center
1205 West State Street
West Lafayette, IN 47907-2057
765-427-4712
-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Anteney I.M.
Sent: Tuesday, September 15, 2015 2:16 AM
To: Dennis Schweiger
Cc: Vito Logiudice; labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] Temperature specification for facility process chilled water
Denis,
I'm particularly interested in your comment about polishing the loops to get 1 mega-ohm resistance as we have struggled to do this especially when we dose the system with biocide and corrosion inhibitors. What are you using to polish the system, what inhibitors/biocides do you use and how do these affect the conductivity.
Regards
Iain
Cleanroom Manager
University of Southampton
Sent from my iPhone
On 15 Sep 2015, at 00:36, Dennis Schweiger <schweig at umich.edu<mailto:schweig at umich.edu><mailto:schweig at umich.edu><mailto:schweig at umich.edu>> wrote:
Vito,
here at UofMichigan, one of our PCW systems runs about 62.5F (16.9C) with a daily deviation of about 1F. The second runs about 59-60F (15C). It too has a daily deviation of about 1F. For both systems we may see a seasonal deviation of 3-4F as the main chiller plant transitions from "free cooling" to the use of chillers to create cooling water for the campus wide loop. We also "polish" both loops to 1 meg-ohm so that we have a "high resistance" in the RF cooling circuits.
Dennis Schweiger
University of Mighigan/LNF
734.647.2055 Ofc
On Fri, Sep 11, 2015 at 3:47 PM, Vito Logiudice <vito.logiudice at uwaterloo.ca<mailto:vito.logiudice at uwaterloo.ca><mailto:vito.logiudice at uwaterloo.ca><mailto:vito.logiudice at uwaterloo.ca>> wrote:
Dear Colleagues,
The process chilled water loop in our cleanroom has consistently oscillated between ~15.4C and ~17.2C over a span of roughly 10 minutes. Our Plant Operations group is looking into the possibility of tightening this up for us by tuning the control sequence. They have asked for guidance on an acceptable specification.
In light of this I would appreciate hearing from you as to your facility's PCW temperature target and tolerance. Thank you much.
Best regards,
Vito
--
Vito Logiudice P.Eng.
Director of Operations, Quantum NanoFab
University of Waterloo
Lazaridis QNC 1207
200 University Avenue West
Waterloo, ON Canada N2L 3G1
Tel.: (519) 888-4567 ext. 38703<tel:%28519%29%20888-4567%20%C2%A0ext.%2038703><tel:%28519%29%20888-4567%20%C2%A0ext.%2038703>
Email: vito.logiudice at uwaterloo.ca<mailto:vito.logiudice at uwaterloo.ca><mailto:vito.logiudice at uwaterloo.ca><mailto:vito.logiudice at uwaterloo.ca>
Website: https://fab.qnc.uwaterloo.ca
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